diff --git a/Cargo.toml b/Cargo.toml
index 6bc713e..65c0cf4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,8 +16,8 @@ travis-ci = {repository = "sile/hls_m3u8"}
 codecov = {repository = "sile/hls_m3u8"}
 
 [dependencies]
-trackable = "0.2"
 getset = "0.0.8"
+failure = "0.1.5"
 
 [dev-dependencies]
 clap = "2"
diff --git a/examples/parse.rs b/examples/parse.rs
index 44a8d16..226a22d 100644
--- a/examples/parse.rs
+++ b/examples/parse.rs
@@ -1,12 +1,9 @@
 extern crate clap;
 extern crate hls_m3u8;
-#[macro_use]
-extern crate trackable;
 
 use clap::{App, Arg};
 use hls_m3u8::{MasterPlaylist, MediaPlaylist};
 use std::io::{self, Read};
-use trackable::error::Failure;
 
 fn main() {
     let matches = App::new("parse")
@@ -19,17 +16,15 @@ fn main() {
         )
         .get_matches();
     let mut m3u8 = String::new();
-    track_try_unwrap!(io::stdin()
-        .read_to_string(&mut m3u8)
-        .map_err(Failure::from_error));
+    io::stdin().read_to_string(&mut m3u8).unwrap();
 
     match matches.value_of("M3U8_TYPE").unwrap() {
         "media" => {
-            let playlist: MediaPlaylist = track_try_unwrap!(m3u8.parse());
+            let playlist: MediaPlaylist = m3u8.parse().unwrap();
             println!("{}", playlist);
         }
         "master" => {
-            let playlist: MasterPlaylist = track_try_unwrap!(m3u8.parse());
+            let playlist: MasterPlaylist = m3u8.parse().unwrap();
             println!("{}", playlist);
         }
         _ => unreachable!(),
diff --git a/src/attribute.rs b/src/attribute.rs
index 8ef7450..212728b 100644
--- a/src/attribute.rs
+++ b/src/attribute.rs
@@ -1,4 +1,4 @@
-use crate::{ErrorKind, Result};
+use crate::{Error, Result};
 use std::collections::HashSet;
 use std::str;
 
@@ -25,18 +25,13 @@ impl<'a> AttributePairs<'a> {
                     return Ok(key);
                 }
                 b'A'..=b'Z' | b'0'..=b'9' | b'-' => {}
-                _ => track_panic!(
-                    ErrorKind::InvalidInput,
-                    "Malformed attribute name: {:?}",
-                    self.input
-                ),
+                _ => {
+                    return Err(Error::invalid_attribute(self.input.to_string()));
+                }
             }
         }
-        track_panic!(
-            ErrorKind::InvalidInput,
-            "No attribute value: {:?}",
-            self.input
-        );
+
+        Err(Error::missing_value(self.input.to_string()))
     }
 
     fn parse_raw_value(&mut self) -> &'a str {
@@ -64,19 +59,15 @@ impl<'a> AttributePairs<'a> {
 }
 impl<'a> Iterator for AttributePairs<'a> {
     type Item = Result<(&'a str, &'a str)>;
+
     fn next(&mut self) -> Option<Self::Item> {
         if self.input.is_empty() {
             return None;
         }
 
         let result = || -> Result<(&'a str, &'a str)> {
-            let key = track!(self.parse_name())?;
-            track_assert!(
-                self.visited_keys.insert(key),
-                ErrorKind::InvalidInput,
-                "Duplicate attribute key: {:?}",
-                key
-            );
+            let key = self.parse_name()?;
+            self.visited_keys.insert(key);
 
             let value = self.parse_raw_value();
             Ok((key, value))
diff --git a/src/error.rs b/src/error.rs
index b803bd1..ff1fddf 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,13 +1,179 @@
-use trackable::error::{ErrorKind as TrackableErrorKind, TrackableError};
+use std::error;
+use std::fmt;
 
-/// This crate specific `Error` type.
-#[derive(Debug, Clone, TrackableError)]
-pub struct Error(TrackableError<ErrorKind>);
+use failure::{Backtrace, Context, Fail};
 
-/// Possible error kinds.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-#[allow(missing_docs)]
-pub enum ErrorKind {
-    InvalidInput,
+/// This crate specific `Result` type.
+pub type Result<T> = std::result::Result<T, Error>;
+
+#[derive(Debug, Fail, Clone)]
+pub enum AttributeError {
+    #[fail(display = "The attribute has an invalid name; {:?}", _0)]
+    InvalidAttribute(String),
+    #[fail(display = "A value is missing for the attribute: {}", _0)]
+    MissingValue(String),
+}
+
+#[derive(Debug, Fail, Clone)]
+pub enum ErrorKind {
+    #[fail(display = "AttributeError: {}", _0)]
+    AttributeError(AttributeError),
+
+    #[fail(display = "UnknownError: {}", _0)]
+    UnknownError(String),
+
+    #[fail(display = "A value is missing for the attribute {}", _0)]
+    MissingValue(String),
+
+    #[fail(display = "Invalid Input")]
+    InvalidInput,
+
+    #[fail(display = "ParseIntError: {}", _0)]
+    ParseIntError(String),
+
+    #[fail(display = "ParseFloatError: {}", _0)]
+    ParseFloatError(String),
+
+    #[fail(display = "MissingTag: Expected {} at the start of {:?}", tag, input)]
+    MissingTag { tag: String, input: String },
+
+    #[fail(display = "CustomError: {}", _0)]
+    Custom(String),
+
+    #[fail(display = "Unmatched Group: {:?}", _0)]
+    UnmatchedGroup(String),
+
+    #[fail(display = "Unknown Protocol version: {:?}", _0)]
+    UnknownProtocolVersion(String),
+
+    /// Hints that destructuring should not be exhaustive.
+    ///
+    /// This enum may grow additional variants, so this makes sure clients
+    /// don't count on exhaustive matching. (Otherwise, adding a new variant
+    /// could break existing code.)
+    #[doc(hidden)]
+    #[fail(display = "Invalid error")]
+    __Nonexhaustive,
+}
+
+#[derive(Debug)]
+pub struct Error {
+    inner: Context<ErrorKind>,
+}
+
+impl Fail for Error {
+    fn cause(&self) -> Option<&dyn Fail> {
+        self.inner.cause()
+    }
+
+    fn backtrace(&self) -> Option<&Backtrace> {
+        self.inner.backtrace()
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl From<ErrorKind> for Error {
+    fn from(kind: ErrorKind) -> Error {
+        Error::from(Context::new(kind))
+    }
+}
+
+impl From<Context<ErrorKind>> for Error {
+    fn from(inner: Context<ErrorKind>) -> Error {
+        Error { inner }
+    }
+}
+
+macro_rules! from_error {
+    ( $( $f:tt ),* ) => {
+        $(
+            impl From<$f> for ErrorKind {
+                fn from(value: $f) -> Self {
+                    Self::$f(value)
+                }
+            }
+        )*
+    }
+}
+
+from_error!(AttributeError);
+
+impl Error {
+    pub(crate) fn invalid_attribute<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::from(AttributeError::InvalidAttribute(
+            value.to_string(),
+        )))
+    }
+
+    pub(crate) fn missing_attribute_value<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::from(AttributeError::MissingValue(
+            value.to_string(),
+        )))
+    }
+
+    pub(crate) fn unknown<T>(value: T) -> Self
+    where
+        T: error::Error,
+    {
+        Self::from(ErrorKind::UnknownError(value.to_string()))
+    }
+
+    pub(crate) fn missing_value<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::MissingValue(value.to_string()))
+    }
+
+    pub(crate) fn invalid_input() -> Self {
+        Self::from(ErrorKind::InvalidInput)
+    }
+
+    pub(crate) fn parse_int_error<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::ParseIntError(value.to_string()))
+    }
+
+    pub(crate) fn parse_float_error<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::ParseFloatError(value.to_string()))
+    }
+
+    pub(crate) fn missing_tag<T, U>(tag: T, input: U) -> Self
+    where
+        T: ToString,
+        U: ToString,
+    {
+        Self::from(ErrorKind::MissingTag {
+            tag: tag.to_string(),
+            input: input.to_string(),
+        })
+    }
+
+    pub(crate) fn unmatched_group<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::UnmatchedGroup(value.to_string()))
+    }
+
+    pub(crate) fn custom<T>(value: T) -> Self
+    where
+        T: fmt::Display,
+    {
+        Self::from(ErrorKind::Custom(value.to_string()))
+    }
+
+    pub(crate) fn unknown_protocol_version<T: ToString>(value: T) -> Self {
+        Self::from(ErrorKind::UnknownProtocolVersion(value.to_string()))
+    }
+}
+
+impl From<std::num::ParseIntError> for Error {
+    fn from(value: ::std::num::ParseIntError) -> Self {
+        Error::parse_int_error(value)
+    }
+}
+
+impl From<std::num::ParseFloatError> for Error {
+    fn from(value: ::std::num::ParseFloatError) -> Self {
+        Error::parse_float_error(value)
+    }
 }
-impl TrackableErrorKind for ErrorKind {}
diff --git a/src/lib.rs b/src/lib.rs
index 409ba59..135c9ef 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,6 +3,7 @@
     clippy::nursery,
     clippy::cargo
 )]
+#![warn(missing_docs)]
 //! [HLS] m3u8 parser/generator.
 //!
 //! [HLS]: https://tools.ietf.org/html/rfc8216
@@ -25,9 +26,6 @@
 //!
 //! assert!(m3u8.parse::<MediaPlaylist>().is_ok());
 //! ```
-#![warn(missing_docs)]
-#[macro_use]
-extern crate trackable;
 
 pub use error::{Error, ErrorKind};
 pub use master_playlist::{MasterPlaylist, MasterPlaylistBuilder};
@@ -45,5 +43,4 @@ mod media_playlist;
 mod media_segment;
 mod utils;
 
-/// This crate specific `Result` type.
-pub type Result<T> = std::result::Result<T, Error>;
+pub use error::Result;
diff --git a/src/line.rs b/src/line.rs
index 974d01d..0641bc5 100644
--- a/src/line.rs
+++ b/src/line.rs
@@ -1,9 +1,10 @@
-use crate::tags;
-use crate::types::SingleLineString;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::tags;
+use crate::types::SingleLineString;
+use crate::Error;
+
 #[derive(Debug)]
 pub struct Lines<'a> {
     input: &'a str,
@@ -13,11 +14,12 @@ impl<'a> Lines<'a> {
         Lines { input }
     }
 
-    fn read_line(&mut self) -> Result<Line<'a>> {
+    fn read_line(&mut self) -> crate::Result<Line<'a>> {
         let mut end = self.input.len();
         let mut next_start = self.input.len();
         let mut adjust = 0;
         let mut next_line_of_ext_x_stream_inf = false;
+
         for (i, c) in self.input.char_indices() {
             match c {
                 '\n' => {
@@ -36,33 +38,39 @@ impl<'a> Lines<'a> {
                     adjust = 1;
                 }
                 _ => {
-                    track_assert!(!c.is_control(), ErrorKind::InvalidInput);
+                    if c.is_control() {
+                        return Err(Error::invalid_input());
+                    }
                     adjust = 0;
                 }
             }
         }
         let raw_line = &self.input[..end];
+
         let line = if raw_line.is_empty() {
             Line::Blank
         } else if raw_line.starts_with("#EXT") {
-            Line::Tag(track!(raw_line.parse())?)
+            Line::Tag((raw_line.parse())?)
         } else if raw_line.starts_with('#') {
             Line::Comment(raw_line)
         } else {
-            let uri = track!(SingleLineString::new(raw_line))?;
+            let uri = SingleLineString::new(raw_line)?;
             Line::Uri(uri)
         };
+
         self.input = &self.input[next_start..];
         Ok(line)
     }
 }
 impl<'a> Iterator for Lines<'a> {
-    type Item = Result<Line<'a>>;
+    type Item = crate::Result<Line<'a>>;
+
     fn next(&mut self) -> Option<Self::Item> {
         if self.input.is_empty() {
             return None;
         }
-        match track!(self.read_line()) {
+
+        match self.read_line() {
             Err(e) => Some(Err(e)),
             Ok(line) => Some(Ok(line)),
         }
@@ -105,6 +113,7 @@ pub enum Tag {
     ExtXStart(tags::ExtXStart),
     Unknown(SingleLineString),
 }
+
 impl fmt::Display for Tag {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
@@ -134,55 +143,57 @@ impl fmt::Display for Tag {
         }
     }
 }
+
 impl FromStr for Tag {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         if s.starts_with(tags::ExtM3u::PREFIX) {
-            track!(s.parse().map(Tag::ExtM3u))
+            (s.parse().map(Tag::ExtM3u))
         } else if s.starts_with(tags::ExtXVersion::PREFIX) {
-            track!(s.parse().map(Tag::ExtXVersion))
+            (s.parse().map(Tag::ExtXVersion))
         } else if s.starts_with(tags::ExtInf::PREFIX) {
-            track!(s.parse().map(Tag::ExtInf))
+            (s.parse().map(Tag::ExtInf))
         } else if s.starts_with(tags::ExtXByteRange::PREFIX) {
-            track!(s.parse().map(Tag::ExtXByteRange))
+            (s.parse().map(Tag::ExtXByteRange))
         } else if s.starts_with(tags::ExtXDiscontinuity::PREFIX) {
-            track!(s.parse().map(Tag::ExtXDiscontinuity))
+            (s.parse().map(Tag::ExtXDiscontinuity))
         } else if s.starts_with(tags::ExtXKey::PREFIX) {
-            track!(s.parse().map(Tag::ExtXKey))
+            (s.parse().map(Tag::ExtXKey))
         } else if s.starts_with(tags::ExtXMap::PREFIX) {
-            track!(s.parse().map(Tag::ExtXMap))
+            (s.parse().map(Tag::ExtXMap))
         } else if s.starts_with(tags::ExtXProgramDateTime::PREFIX) {
-            track!(s.parse().map(Tag::ExtXProgramDateTime))
+            (s.parse().map(Tag::ExtXProgramDateTime))
         } else if s.starts_with(tags::ExtXTargetDuration::PREFIX) {
-            track!(s.parse().map(Tag::ExtXTargetDuration))
+            (s.parse().map(Tag::ExtXTargetDuration))
         } else if s.starts_with(tags::ExtXDateRange::PREFIX) {
-            track!(s.parse().map(Tag::ExtXDateRange))
+            (s.parse().map(Tag::ExtXDateRange))
         } else if s.starts_with(tags::ExtXMediaSequence::PREFIX) {
-            track!(s.parse().map(Tag::ExtXMediaSequence))
+            (s.parse().map(Tag::ExtXMediaSequence))
         } else if s.starts_with(tags::ExtXDiscontinuitySequence::PREFIX) {
-            track!(s.parse().map(Tag::ExtXDiscontinuitySequence))
+            (s.parse().map(Tag::ExtXDiscontinuitySequence))
         } else if s.starts_with(tags::ExtXEndList::PREFIX) {
-            track!(s.parse().map(Tag::ExtXEndList))
+            (s.parse().map(Tag::ExtXEndList))
         } else if s.starts_with(tags::ExtXPlaylistType::PREFIX) {
-            track!(s.parse().map(Tag::ExtXPlaylistType))
+            (s.parse().map(Tag::ExtXPlaylistType))
         } else if s.starts_with(tags::ExtXIFramesOnly::PREFIX) {
-            track!(s.parse().map(Tag::ExtXIFramesOnly))
+            (s.parse().map(Tag::ExtXIFramesOnly))
         } else if s.starts_with(tags::ExtXMedia::PREFIX) {
-            track!(s.parse().map(Tag::ExtXMedia))
+            (s.parse().map(Tag::ExtXMedia))
         } else if s.starts_with(tags::ExtXStreamInf::PREFIX) {
-            track!(s.parse().map(Tag::ExtXStreamInf))
+            (s.parse().map(Tag::ExtXStreamInf))
         } else if s.starts_with(tags::ExtXIFrameStreamInf::PREFIX) {
-            track!(s.parse().map(Tag::ExtXIFrameStreamInf))
+            (s.parse().map(Tag::ExtXIFrameStreamInf))
         } else if s.starts_with(tags::ExtXSessionData::PREFIX) {
-            track!(s.parse().map(Tag::ExtXSessionData))
+            (s.parse().map(Tag::ExtXSessionData))
         } else if s.starts_with(tags::ExtXSessionKey::PREFIX) {
-            track!(s.parse().map(Tag::ExtXSessionKey))
+            (s.parse().map(Tag::ExtXSessionKey))
         } else if s.starts_with(tags::ExtXIndependentSegments::PREFIX) {
-            track!(s.parse().map(Tag::ExtXIndependentSegments))
+            (s.parse().map(Tag::ExtXIndependentSegments))
         } else if s.starts_with(tags::ExtXStart::PREFIX) {
-            track!(s.parse().map(Tag::ExtXStart))
+            (s.parse().map(Tag::ExtXStart))
         } else {
-            track!(SingleLineString::new(s)).map(Tag::Unknown)
+            SingleLineString::new(s).map(Tag::Unknown)
         }
     }
 }
diff --git a/src/master_playlist.rs b/src/master_playlist.rs
index 48a4453..5ce9a38 100644
--- a/src/master_playlist.rs
+++ b/src/master_playlist.rs
@@ -1,14 +1,15 @@
+use std::collections::HashSet;
+use std::fmt;
+use std::iter;
+use std::str::FromStr;
+
 use crate::line::{Line, Lines, Tag};
 use crate::tags::{
     ExtM3u, ExtXIFrameStreamInf, ExtXIndependentSegments, ExtXMedia, ExtXSessionData,
     ExtXSessionKey, ExtXStart, ExtXStreamInf, ExtXVersion, MasterPlaylistTag,
 };
 use crate::types::{ClosedCaptions, MediaType, ProtocolVersion};
-use crate::{Error, ErrorKind, Result};
-use std::collections::HashSet;
-use std::fmt;
-use std::iter;
-use std::str::FromStr;
+use crate::{Error, Result};
 
 /// Master playlist builder.
 #[derive(Debug, Clone)]
@@ -71,18 +72,16 @@ impl MasterPlaylistBuilder {
     pub fn finish(self) -> Result<MasterPlaylist> {
         let required_version = self.required_version();
         let specified_version = self.version.unwrap_or(required_version);
-        track_assert!(
-            required_version <= specified_version,
-            ErrorKind::InvalidInput,
-            "required_version:{}, specified_version:{}",
-            required_version,
-            specified_version,
-        );
 
-        track!(self.validate_stream_inf_tags())?;
-        track!(self.validate_i_frame_stream_inf_tags())?;
-        track!(self.validate_session_data_tags())?;
-        track!(self.validate_session_key_tags())?;
+        if required_version <= specified_version {
+            // "required_version:{}, specified_version:{}"
+            return Err(Error::invalid_input());
+        }
+
+        (self.validate_stream_inf_tags())?;
+        (self.validate_i_frame_stream_inf_tags())?;
+        (self.validate_session_data_tags())?;
+        (self.validate_session_key_tags())?;
 
         Ok(MasterPlaylist {
             version_tag: ExtXVersion::new(specified_version),
@@ -121,37 +120,25 @@ impl MasterPlaylistBuilder {
         let mut has_none_closed_captions = false;
         for t in &self.stream_inf_tags {
             if let Some(group_id) = t.audio() {
-                track_assert!(
-                    self.check_media_group(MediaType::Audio, group_id),
-                    ErrorKind::InvalidInput,
-                    "Unmatched audio group: {:?}",
-                    group_id
-                );
+                if !self.check_media_group(MediaType::Audio, group_id) {
+                    return Err(Error::unmatched_group(group_id));
+                }
             }
             if let Some(group_id) = t.video() {
-                track_assert!(
-                    self.check_media_group(MediaType::Video, group_id),
-                    ErrorKind::InvalidInput,
-                    "Unmatched video group: {:?}",
-                    group_id
-                );
+                if !self.check_media_group(MediaType::Video, group_id) {
+                    return Err(Error::unmatched_group(group_id));
+                }
             }
             if let Some(group_id) = t.subtitles() {
-                track_assert!(
-                    self.check_media_group(MediaType::Subtitles, group_id),
-                    ErrorKind::InvalidInput,
-                    "Unmatched subtitles group: {:?}",
-                    group_id
-                );
+                if !self.check_media_group(MediaType::Subtitles, group_id) {
+                    return Err(Error::unmatched_group(group_id));
+                }
             }
             match t.closed_captions() {
                 Some(&ClosedCaptions::GroupId(ref group_id)) => {
-                    track_assert!(
-                        self.check_media_group(MediaType::ClosedCaptions, group_id),
-                        ErrorKind::InvalidInput,
-                        "Unmatched closed-captions group: {:?}",
-                        group_id
-                    );
+                    if !self.check_media_group(MediaType::ClosedCaptions, group_id) {
+                        return Err(Error::unmatched_group(group_id));
+                    }
                 }
                 Some(&ClosedCaptions::None) => {
                     has_none_closed_captions = true;
@@ -160,53 +147,49 @@ impl MasterPlaylistBuilder {
             }
         }
         if has_none_closed_captions {
-            track_assert!(
-                self.stream_inf_tags
-                    .iter()
-                    .all(|t| t.closed_captions() == Some(&ClosedCaptions::None)),
-                ErrorKind::InvalidInput
-            );
+            if !self
+                .stream_inf_tags
+                .iter()
+                .all(|t| t.closed_captions() == Some(&ClosedCaptions::None))
+            {
+                return Err(Error::invalid_input());
+            }
         }
+
         Ok(())
     }
 
     fn validate_i_frame_stream_inf_tags(&self) -> Result<()> {
         for t in &self.i_frame_stream_inf_tags {
             if let Some(group_id) = t.video() {
-                track_assert!(
-                    self.check_media_group(MediaType::Video, group_id),
-                    ErrorKind::InvalidInput,
-                    "Unmatched video group: {:?}",
-                    group_id
-                );
+                if !self.check_media_group(MediaType::Video, group_id) {
+                    return Err(Error::unmatched_group(group_id));
+                }
             }
         }
+
         Ok(())
     }
 
     fn validate_session_data_tags(&self) -> Result<()> {
         let mut set = HashSet::new();
         for t in &self.session_data_tags {
-            track_assert!(
-                set.insert((t.data_id(), t.language())),
-                ErrorKind::InvalidInput,
-                "Conflict: {}",
-                t
-            );
+            if !set.insert((t.data_id(), t.language())) {
+                return Err(Error::custom(format!("Conflict: {}", t)));
+            }
         }
+
         Ok(())
     }
 
     fn validate_session_key_tags(&self) -> Result<()> {
         let mut set = HashSet::new();
         for t in &self.session_key_tags {
-            track_assert!(
-                set.insert(t.key()),
-                ErrorKind::InvalidInput,
-                "Conflict: {}",
-                t
-            );
+            if !set.insert(t.key()) {
+                return Err(Error::custom(format!("Conflict: {}", t)));
+            }
         }
+
         Ok(())
     }
 
@@ -308,24 +291,29 @@ impl fmt::Display for MasterPlaylist {
         Ok(())
     }
 }
+
 impl FromStr for MasterPlaylist {
     type Err = Error;
     fn from_str(s: &str) -> Result<Self> {
         let mut builder = MasterPlaylistBuilder::new();
         for (i, line) in Lines::new(s).enumerate() {
-            match track!(line)? {
+            match (line)? {
                 Line::Blank | Line::Comment(_) => {}
                 Line::Tag(tag) => {
                     if i == 0 {
-                        track_assert_eq!(tag, Tag::ExtM3u(ExtM3u), ErrorKind::InvalidInput);
+                        if tag != Tag::ExtM3u(ExtM3u) {
+                            return Err(Error::invalid_input());
+                        }
                         continue;
                     }
                     match tag {
                         Tag::ExtM3u(_) => {
-                            track_panic!(ErrorKind::InvalidInput);
+                            return Err(Error::invalid_input());
                         }
                         Tag::ExtXVersion(t) => {
-                            track_assert_eq!(builder.version, None, ErrorKind::InvalidInput);
+                            if builder.version.is_some() {
+                                return Err(Error::invalid_input());
+                            }
                             builder.version(t.version());
                         }
                         Tag::ExtInf(_)
@@ -341,7 +329,7 @@ impl FromStr for MasterPlaylist {
                         | Tag::ExtXEndList(_)
                         | Tag::ExtXPlaylistType(_)
                         | Tag::ExtXIFramesOnly(_) => {
-                            track_panic!(ErrorKind::InvalidInput, "{}", tag)
+                            return Err(Error::invalid_input()); // TODO: why?
                         }
                         Tag::ExtXMedia(t) => {
                             builder.tag(t);
@@ -359,28 +347,29 @@ impl FromStr for MasterPlaylist {
                             builder.tag(t);
                         }
                         Tag::ExtXIndependentSegments(t) => {
-                            track_assert_eq!(
-                                builder.independent_segments_tag,
-                                None,
-                                ErrorKind::InvalidInput
-                            );
+                            if builder.independent_segments_tag.is_some() {
+                                return Err(Error::invalid_input());
+                            }
                             builder.tag(t);
                         }
                         Tag::ExtXStart(t) => {
-                            track_assert_eq!(builder.start_tag, None, ErrorKind::InvalidInput);
+                            if builder.start_tag.is_some() {
+                                return Err(Error::invalid_input());
+                            }
                             builder.tag(t);
                         }
                         Tag::Unknown(_) => {
                             // [6.3.1. General Client Responsibilities]
                             // > ignore any unrecognized tags.
+                            // TODO: collect custom tags
                         }
                     }
                 }
                 Line::Uri(uri) => {
-                    track_panic!(ErrorKind::InvalidInput, "Unexpected URI: {:?}", uri);
+                    return Err(Error::custom(format!("Unexpected URI: {:?}", uri)));
                 }
             }
         }
-        track!(builder.finish())
+        builder.finish()
     }
 }
diff --git a/src/media_playlist.rs b/src/media_playlist.rs
index 5eca286..0b09225 100644
--- a/src/media_playlist.rs
+++ b/src/media_playlist.rs
@@ -1,3 +1,8 @@
+use std::fmt;
+use std::iter;
+use std::str::FromStr;
+use std::time::Duration;
+
 use crate::line::{Line, Lines, Tag};
 use crate::media_segment::{MediaSegment, MediaSegmentBuilder};
 use crate::tags::{
@@ -6,11 +11,7 @@ use crate::tags::{
     MediaPlaylistTag,
 };
 use crate::types::ProtocolVersion;
-use crate::{Error, ErrorKind, Result};
-use std::fmt;
-use std::iter;
-use std::str::FromStr;
-use std::time::Duration;
+use crate::Error;
 
 /// Media playlist builder.
 #[derive(Debug, Clone)]
@@ -89,20 +90,18 @@ impl MediaPlaylistBuilder {
     }
 
     /// Builds a `MediaPlaylist` instance.
-    pub fn finish(self) -> Result<MediaPlaylist> {
+    pub fn finish(self) -> crate::Result<MediaPlaylist> {
         let required_version = self.required_version();
         let specified_version = self.version.unwrap_or(required_version);
-        track_assert!(
-            required_version <= specified_version,
-            ErrorKind::InvalidInput,
-            "required_version:{}, specified_version:{}",
-            required_version,
-            specified_version,
-        );
+        if !(required_version <= specified_version) {
+            return Err(Error::custom(format!(
+                "required_version:{}, specified_version:{}",
+                required_version, specified_version
+            )));
+        }
 
-        let target_duration_tag =
-            track_assert_some!(self.target_duration_tag, ErrorKind::InvalidInput);
-        track!(self.validate_media_segments(target_duration_tag.duration()))?;
+        let target_duration_tag = self.target_duration_tag.ok_or(Error::invalid_input())?;
+        self.validate_media_segments(target_duration_tag.duration())?;
 
         Ok(MediaPlaylist {
             version_tag: ExtXVersion::new(specified_version),
@@ -118,7 +117,7 @@ impl MediaPlaylistBuilder {
         })
     }
 
-    fn validate_media_segments(&self, target_duration: Duration) -> Result<()> {
+    fn validate_media_segments(&self, target_duration: Duration) -> crate::Result<()> {
         let mut last_range_uri = None;
         for s in &self.segments {
             // CHECK: `#EXT-X-TARGETDURATION`
@@ -129,21 +128,24 @@ impl MediaPlaylistBuilder {
                 Duration::from_secs(segment_duration.as_secs() + 1)
             };
             let max_segment_duration = target_duration + self.options.allowable_excess_duration;
-            track_assert!(
-                rounded_segment_duration <= max_segment_duration,
-                ErrorKind::InvalidInput,
-                "Too large segment duration: actual={:?}, max={:?}, target_duration={:?}, uri={:?}",
-                segment_duration,
-                max_segment_duration,
-                target_duration,
-                s.uri()
-            );
+
+            if !(rounded_segment_duration <= max_segment_duration) {
+                return Err(Error::custom(format!(
+                    "Too large segment duration: actual={:?}, max={:?}, target_duration={:?}, uri={:?}",
+                    segment_duration,
+                    max_segment_duration,
+                    target_duration,
+                    s.uri()
+                )));
+            }
 
             // CHECK: `#EXT-X-BYTE-RANGE`
             if let Some(tag) = s.byte_range_tag() {
                 if tag.to_range().start().is_none() {
-                    let last_uri = track_assert_some!(last_range_uri, ErrorKind::InvalidInput);
-                    track_assert_eq!(last_uri, s.uri(), ErrorKind::InvalidInput);
+                    let last_uri = last_range_uri.ok_or(Error::invalid_input())?;
+                    if last_uri != s.uri() {
+                        return Err(Error::invalid_input());
+                    }
                 } else {
                     last_range_uri = Some(s.uri());
                 }
@@ -292,8 +294,9 @@ impl fmt::Display for MediaPlaylist {
 
 impl FromStr for MediaPlaylist {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track!(MediaPlaylistOptions::new().parse(s))
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        MediaPlaylistOptions::new().parse(input)
     }
 }
 
@@ -305,7 +308,7 @@ pub struct MediaPlaylistOptions {
 
 impl MediaPlaylistOptions {
     /// Makes a new `MediaPlaylistOptions` with the default settings.
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         MediaPlaylistOptions {
             allowable_excess_duration: Duration::from_secs(0),
         }
@@ -327,7 +330,7 @@ impl MediaPlaylistOptions {
     }
 
     /// Parses the given M3U8 text with the specified settings.
-    pub fn parse(&self, m3u8: &str) -> Result<MediaPlaylist> {
+    pub fn parse(&self, m3u8: &str) -> crate::Result<MediaPlaylist> {
         let mut builder = MediaPlaylistBuilder::new();
         builder.options(self.clone());
 
@@ -335,17 +338,21 @@ impl MediaPlaylistOptions {
         let mut has_partial_segment = false;
         let mut has_discontinuity_tag = false;
         for (i, line) in Lines::new(m3u8).enumerate() {
-            match track!(line)? {
+            match (line)? {
                 Line::Blank | Line::Comment(_) => {}
                 Line::Tag(tag) => {
                     if i == 0 {
-                        track_assert_eq!(tag, Tag::ExtM3u(ExtM3u), ErrorKind::InvalidInput);
+                        if tag != Tag::ExtM3u(ExtM3u) {
+                            return Err(Error::invalid_input());
+                        }
                         continue;
                     }
                     match tag {
-                        Tag::ExtM3u(_) => track_panic!(ErrorKind::InvalidInput),
+                        Tag::ExtM3u(_) => return Err(Error::invalid_input()),
                         Tag::ExtXVersion(t) => {
-                            track_assert_eq!(builder.version, None, ErrorKind::InvalidInput);
+                            if builder.version.is_some() {
+                                return Err(Error::invalid_input());
+                            }
                             builder.version(t.version());
                         }
                         Tag::ExtInf(t) => {
@@ -378,45 +385,30 @@ impl MediaPlaylistOptions {
                             segment.tag(t);
                         }
                         Tag::ExtXTargetDuration(t) => {
-                            track_assert_eq!(
-                                builder.target_duration_tag,
-                                None,
-                                ErrorKind::InvalidInput
-                            );
                             builder.tag(t);
                         }
                         Tag::ExtXMediaSequence(t) => {
-                            track_assert_eq!(
-                                builder.media_sequence_tag,
-                                None,
-                                ErrorKind::InvalidInput
-                            );
-                            track_assert!(builder.segments.is_empty(), ErrorKind::InvalidInput);
+                            if builder.segments.is_empty() {
+                                return Err(Error::invalid_input());
+                            }
                             builder.tag(t);
                         }
                         Tag::ExtXDiscontinuitySequence(t) => {
-                            track_assert!(builder.segments.is_empty(), ErrorKind::InvalidInput);
-                            track_assert!(!has_discontinuity_tag, ErrorKind::InvalidInput);
+                            if builder.segments.is_empty() {
+                                return Err(Error::invalid_input());
+                            }
+                            if has_discontinuity_tag {
+                                return Err(Error::invalid_input());
+                            }
                             builder.tag(t);
                         }
                         Tag::ExtXEndList(t) => {
-                            track_assert_eq!(builder.end_list_tag, None, ErrorKind::InvalidInput);
                             builder.tag(t);
                         }
                         Tag::ExtXPlaylistType(t) => {
-                            track_assert_eq!(
-                                builder.playlist_type_tag,
-                                None,
-                                ErrorKind::InvalidInput
-                            );
                             builder.tag(t);
                         }
                         Tag::ExtXIFramesOnly(t) => {
-                            track_assert_eq!(
-                                builder.i_frames_only_tag,
-                                None,
-                                ErrorKind::InvalidInput
-                            );
                             builder.tag(t);
                         }
                         Tag::ExtXMedia(_)
@@ -424,18 +416,12 @@ impl MediaPlaylistOptions {
                         | Tag::ExtXIFrameStreamInf(_)
                         | Tag::ExtXSessionData(_)
                         | Tag::ExtXSessionKey(_) => {
-                            track_panic!(ErrorKind::InvalidInput, "{}", tag)
+                            return Err(Error::custom(tag));
                         }
                         Tag::ExtXIndependentSegments(t) => {
-                            track_assert_eq!(
-                                builder.independent_segments_tag,
-                                None,
-                                ErrorKind::InvalidInput
-                            );
                             builder.tag(t);
                         }
                         Tag::ExtXStart(t) => {
-                            track_assert_eq!(builder.start_tag, None, ErrorKind::InvalidInput);
                             builder.tag(t);
                         }
                         Tag::Unknown(_) => {
@@ -446,14 +432,16 @@ impl MediaPlaylistOptions {
                 }
                 Line::Uri(uri) => {
                     segment.uri(uri);
-                    builder.segment(track!(segment.finish())?);
+                    builder.segment((segment.finish())?);
                     segment = MediaSegmentBuilder::new();
                     has_partial_segment = false;
                 }
             }
         }
-        track_assert!(!has_partial_segment, ErrorKind::InvalidInput);
-        track!(builder.finish())
+        if has_partial_segment {
+            return Err(Error::invalid_input());
+        }
+        builder.finish()
     }
 }
 
diff --git a/src/media_segment.rs b/src/media_segment.rs
index 602b51d..3f45f5b 100644
--- a/src/media_segment.rs
+++ b/src/media_segment.rs
@@ -1,11 +1,12 @@
+use std::fmt;
+use std::iter;
+
 use crate::tags::{
     ExtInf, ExtXByteRange, ExtXDateRange, ExtXDiscontinuity, ExtXKey, ExtXMap, ExtXProgramDateTime,
     MediaSegmentTag,
 };
 use crate::types::{ProtocolVersion, SingleLineString};
-use crate::{ErrorKind, Result};
-use std::fmt;
-use std::iter;
+use crate::Error;
 
 /// Media segment builder.
 #[derive(Debug, Clone)]
@@ -56,9 +57,10 @@ impl MediaSegmentBuilder {
     }
 
     /// Builds a `MediaSegment` instance.
-    pub fn finish(self) -> Result<MediaSegment> {
-        let uri = track_assert_some!(self.uri, ErrorKind::InvalidInput);
-        let inf_tag = track_assert_some!(self.inf_tag, ErrorKind::InvalidInput);
+    pub fn finish(self) -> crate::Result<MediaSegment> {
+        let uri = self.uri.ok_or(Error::missing_value("self.uri"))?;
+        let inf_tag = self.inf_tag.ok_or(Error::missing_value("self.inf_tag"))?;
+
         Ok(MediaSegment {
             key_tags: self.key_tags,
             map_tag: self.map_tag,
diff --git a/src/tags/master_playlist/i_frame_stream_inf.rs b/src/tags/master_playlist/i_frame_stream_inf.rs
index f9e38dc..7f9abd3 100644
--- a/src/tags/master_playlist/i_frame_stream_inf.rs
+++ b/src/tags/master_playlist/i_frame_stream_inf.rs
@@ -7,7 +7,7 @@ use crate::attribute::AttributePairs;
 use crate::types::{DecimalResolution, HdcpLevel, ProtocolVersion};
 use crate::utils::parse_u64;
 use crate::utils::{quote, tag, unquote};
-use crate::{Error, ErrorKind};
+use crate::Error;
 
 /// [4.3.4.3. EXT-X-I-FRAME-STREAM-INF]
 ///
@@ -96,14 +96,14 @@ impl FromStr for ExtXIFrameStreamInf {
 
         let attrs = AttributePairs::parse(input);
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = attr?;
             match key {
                 "URI" => uri = Some(unquote(value)),
-                "BANDWIDTH" => bandwidth = Some(track!(parse_u64(value))?),
-                "AVERAGE-BANDWIDTH" => average_bandwidth = Some(track!(parse_u64(value))?),
+                "BANDWIDTH" => bandwidth = Some(parse_u64(value)?),
+                "AVERAGE-BANDWIDTH" => average_bandwidth = Some(parse_u64(value)?),
                 "CODECS" => codecs = Some(unquote(value)),
-                "RESOLUTION" => resolution = Some(track!(value.parse())?),
-                "HDCP-LEVEL" => hdcp_level = Some(track!(value.parse())?),
+                "RESOLUTION" => resolution = Some(value.parse()?),
+                "HDCP-LEVEL" => hdcp_level = Some(value.parse()?),
                 "VIDEO" => video = Some(unquote(value)),
                 _ => {
                     // [6.3.1. General Client Responsibilities]
@@ -112,8 +112,9 @@ impl FromStr for ExtXIFrameStreamInf {
             }
         }
 
-        let uri = track_assert_some!(uri, ErrorKind::InvalidInput);
-        let bandwidth = track_assert_some!(bandwidth, ErrorKind::InvalidInput);
+        let uri = uri.ok_or(Error::missing_value("URI"))?;
+        let bandwidth = bandwidth.ok_or(Error::missing_value("BANDWIDTH"))?;
+
         Ok(ExtXIFrameStreamInf {
             uri,
             bandwidth,
diff --git a/src/tags/master_playlist/media.rs b/src/tags/master_playlist/media.rs
index 59e2910..40d1e41 100644
--- a/src/tags/master_playlist/media.rs
+++ b/src/tags/master_playlist/media.rs
@@ -1,9 +1,10 @@
+use std::fmt;
+use std::str::FromStr;
+
 use crate::attribute::AttributePairs;
 use crate::types::{InStreamId, MediaType, ProtocolVersion};
 use crate::utils::{parse_yes_or_no, quote, tag, unquote};
-use crate::{Error, ErrorKind};
-use std::fmt;
-use std::str::FromStr;
+use crate::Error;
 
 /// `ExtXMedia` builder.
 #[derive(Debug, Clone)]
@@ -115,21 +116,38 @@ impl ExtXMediaBuilder {
 
     /// Builds a `ExtXMedia` instance.
     pub fn finish(self) -> crate::Result<ExtXMedia> {
-        let media_type = track_assert_some!(self.media_type, ErrorKind::InvalidInput);
-        let group_id = track_assert_some!(self.group_id, ErrorKind::InvalidInput);
-        let name = track_assert_some!(self.name, ErrorKind::InvalidInput);
+        let media_type = self
+            .media_type
+            .ok_or(Error::missing_value("self.media_type"))?;
+        let group_id = self.group_id.ok_or(Error::missing_value("self.group_id"))?;
+        let name = self.name.ok_or(Error::missing_value("self.name"))?;
+
         if MediaType::ClosedCaptions == media_type {
-            track_assert_ne!(self.uri, None, ErrorKind::InvalidInput);
-            track_assert!(self.instream_id.is_some(), ErrorKind::InvalidInput);
+            if let None = self.uri {
+                return Err(Error::missing_value("self.uri"));
+            }
+            self.instream_id
+                .ok_or(Error::missing_value("self.instream_id"))?;
         } else {
-            track_assert!(self.instream_id.is_none(), ErrorKind::InvalidInput);
+            if let Some(_) = &self.instream_id {
+                Err(Error::invalid_input())?;
+            }
         }
+
         if self.default && self.autoselect.is_some() {
-            track_assert_eq!(self.autoselect, Some(true), ErrorKind::InvalidInput);
+            if let Some(value) = &self.autoselect {
+                if *value {
+                    Err(Error::invalid_input())?;
+                }
+            }
         }
+
         if MediaType::Subtitles != media_type {
-            track_assert_eq!(self.forced, None, ErrorKind::InvalidInput);
+            if self.forced.is_some() {
+                Err(Error::invalid_input())?;
+            }
         }
+
         Ok(ExtXMedia {
             media_type,
             uri: self.uri,
@@ -315,10 +333,10 @@ impl FromStr for ExtXMedia {
         let mut builder = ExtXMediaBuilder::new();
         let attrs = AttributePairs::parse(input);
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = attr?;
             match key {
                 "TYPE" => {
-                    builder.media_type(track!(value.parse())?);
+                    builder.media_type(value.parse()?);
                 }
                 "URI" => {
                     builder.uri(unquote(value));
@@ -336,13 +354,13 @@ impl FromStr for ExtXMedia {
                     builder.name(unquote(value));
                 }
                 "DEFAULT" => {
-                    builder.default(track!(parse_yes_or_no(value))?);
+                    builder.default((parse_yes_or_no(value))?);
                 }
                 "AUTOSELECT" => {
-                    builder.autoselect(track!(parse_yes_or_no(value))?);
+                    builder.autoselect((parse_yes_or_no(value))?);
                 }
                 "FORCED" => {
-                    builder.forced(track!(parse_yes_or_no(value))?);
+                    builder.forced((parse_yes_or_no(value))?);
                 }
                 "INSTREAM-ID" => {
                     builder.instream_id(unquote(value).parse()?);
@@ -359,7 +377,7 @@ impl FromStr for ExtXMedia {
                 }
             }
         }
-        track!(builder.finish())
+        (builder.finish())
     }
 }
 
diff --git a/src/tags/master_playlist/session_data.rs b/src/tags/master_playlist/session_data.rs
index 97da40d..f246862 100644
--- a/src/tags/master_playlist/session_data.rs
+++ b/src/tags/master_playlist/session_data.rs
@@ -6,7 +6,7 @@ use getset::{Getters, MutGetters, Setters};
 use crate::attribute::AttributePairs;
 use crate::types::{ProtocolVersion, SessionData};
 use crate::utils::{quote, tag, unquote};
-use crate::{Error, ErrorKind};
+use crate::Error;
 
 /// [4.3.4.4. EXT-X-SESSION-DATA]
 ///
@@ -79,7 +79,7 @@ impl FromStr for ExtXSessionData {
 
         let attrs = AttributePairs::parse(input);
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = attr?;
             match key {
                 "DATA-ID" => data_id = Some(unquote(value)),
                 "VALUE" => session_value = Some(unquote(value)),
@@ -92,15 +92,21 @@ impl FromStr for ExtXSessionData {
             }
         }
 
-        let data_id = track_assert_some!(data_id, ErrorKind::InvalidInput);
-        let data = if let Some(value) = session_value {
-            track_assert_eq!(uri, None, ErrorKind::InvalidInput);
-            SessionData::Value(value)
-        } else if let Some(uri) = uri {
-            SessionData::Uri(uri)
-        } else {
-            track_panic!(ErrorKind::InvalidInput);
+        let data_id = data_id.ok_or(Error::missing_value("DATA-ID"))?;
+        let data = {
+            if let Some(value) = session_value {
+                if uri.is_some() {
+                    return Err(Error::invalid_input());
+                } else {
+                    SessionData::Value(value)
+                }
+            } else if let Some(uri) = uri {
+                SessionData::Uri(uri)
+            } else {
+                return Err(Error::invalid_input());
+            }
         };
+
         Ok(ExtXSessionData {
             data_id,
             data,
diff --git a/src/tags/master_playlist/stream_inf.rs b/src/tags/master_playlist/stream_inf.rs
index dbeeef9..e69df8b 100644
--- a/src/tags/master_playlist/stream_inf.rs
+++ b/src/tags/master_playlist/stream_inf.rs
@@ -7,7 +7,7 @@ use crate::types::{
     SingleLineString,
 };
 use crate::utils::{parse_u64, quote, tag, unquote};
-use crate::{Error, ErrorKind};
+use crate::Error;
 
 /// [4.3.4.2. EXT-X-STREAM-INF]
 ///
@@ -149,12 +149,12 @@ impl FromStr for ExtXStreamInf {
 
     fn from_str(input: &str) -> Result<Self, Self::Err> {
         let mut lines = input.lines();
-        let first_line = lines.next().ok_or(ErrorKind::InvalidInput)?; // TODO!
-        let second_line = lines.next().ok_or(ErrorKind::InvalidInput)?; // TODO!
+        let first_line = lines.next().ok_or(Error::invalid_input())?; // TODO!
+        let second_line = lines.next().ok_or(Error::invalid_input())?; // TODO!
 
         tag(first_line, Self::PREFIX)?;
 
-        let uri = track!(SingleLineString::new(second_line))?;
+        let uri = SingleLineString::new(second_line)?;
 
         let mut bandwidth = None;
         let mut average_bandwidth = None;
@@ -166,20 +166,21 @@ impl FromStr for ExtXStreamInf {
         let mut video = None;
         let mut subtitles = None;
         let mut closed_captions = None;
+
         let attrs = AttributePairs::parse(first_line.split_at(Self::PREFIX.len()).1);
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = (attr)?;
             match key {
-                "BANDWIDTH" => bandwidth = Some(track!(parse_u64(value))?),
-                "AVERAGE-BANDWIDTH" => average_bandwidth = Some(track!(parse_u64(value))?),
+                "BANDWIDTH" => bandwidth = Some((parse_u64(value))?),
+                "AVERAGE-BANDWIDTH" => average_bandwidth = Some((parse_u64(value))?),
                 "CODECS" => codecs = Some(unquote(value)),
-                "RESOLUTION" => resolution = Some(track!(value.parse())?),
-                "FRAME-RATE" => frame_rate = Some(track!(value.parse())?),
-                "HDCP-LEVEL" => hdcp_level = Some(track!(value.parse())?),
+                "RESOLUTION" => resolution = Some((value.parse())?),
+                "FRAME-RATE" => frame_rate = Some((value.parse())?),
+                "HDCP-LEVEL" => hdcp_level = Some((value.parse())?),
                 "AUDIO" => audio = Some(unquote(value)),
                 "VIDEO" => video = Some(unquote(value)),
                 "SUBTITLES" => subtitles = Some(unquote(value)),
-                "CLOSED-CAPTIONS" => closed_captions = Some(track!(value.parse())?),
+                "CLOSED-CAPTIONS" => closed_captions = Some((value.parse())?),
                 _ => {
                     // [6.3.1. General Client Responsibilities]
                     // > ignore any attribute/value pair with an unrecognized AttributeName.
@@ -187,7 +188,8 @@ impl FromStr for ExtXStreamInf {
             }
         }
 
-        let bandwidth = track_assert_some!(bandwidth, ErrorKind::InvalidInput);
+        let bandwidth = bandwidth.ok_or(Error::missing_value("BANDWIDTH"))?;
+
         Ok(ExtXStreamInf {
             uri,
             bandwidth,
diff --git a/src/tags/media_playlist/end_list.rs b/src/tags/media_playlist/end_list.rs
index ddeb5c0..b34b357 100644
--- a/src/tags/media_playlist/end_list.rs
+++ b/src/tags/media_playlist/end_list.rs
@@ -1,8 +1,10 @@
-use crate::types::ProtocolVersion;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::types::ProtocolVersion;
+use crate::utils::tag;
+use crate::Error;
+
 /// [4.3.3.4. EXT-X-ENDLIST]
 ///
 /// [4.3.3.4. EXT-X-ENDLIST]: https://tools.ietf.org/html/rfc8216#section-4.3.3.4
@@ -26,8 +28,8 @@ impl fmt::Display for ExtXEndList {
 impl FromStr for ExtXEndList {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert_eq!(s, Self::PREFIX, ErrorKind::InvalidInput);
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        tag(input, Self::PREFIX)?;
         Ok(ExtXEndList)
     }
 }
diff --git a/src/tags/media_playlist/i_frames_only.rs b/src/tags/media_playlist/i_frames_only.rs
index 90db7f4..dfe3abc 100644
--- a/src/tags/media_playlist/i_frames_only.rs
+++ b/src/tags/media_playlist/i_frames_only.rs
@@ -1,8 +1,10 @@
-use crate::types::ProtocolVersion;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::types::ProtocolVersion;
+use crate::utils::tag;
+use crate::Error;
+
 /// [4.3.3.6. EXT-X-I-FRAMES-ONLY]
 ///
 /// [4.3.3.6. EXT-X-I-FRAMES-ONLY]: https://tools.ietf.org/html/rfc8216#section-4.3.3.6
@@ -27,8 +29,8 @@ impl fmt::Display for ExtXIFramesOnly {
 impl FromStr for ExtXIFramesOnly {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert_eq!(s, Self::PREFIX, ErrorKind::InvalidInput);
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        tag(input, Self::PREFIX)?;
         Ok(ExtXIFramesOnly)
     }
 }
diff --git a/src/tags/media_playlist/media_sequence.rs b/src/tags/media_playlist/media_sequence.rs
index 47f75bf..1f328f0 100644
--- a/src/tags/media_playlist/media_sequence.rs
+++ b/src/tags/media_playlist/media_sequence.rs
@@ -1,8 +1,9 @@
-use crate::types::ProtocolVersion;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
-use trackable::error::ErrorKindExt;
+
+use crate::types::ProtocolVersion;
+use crate::utils::tag;
+use crate::Error;
 
 /// [4.3.3.2. EXT-X-MEDIA-SEQUENCE]
 ///
@@ -40,10 +41,10 @@ impl fmt::Display for ExtXMediaSequence {
 impl FromStr for ExtXMediaSequence {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let seq_num = may_invalid!(s.split_at(Self::PREFIX.len()).1.parse())?;
-        Ok(ExtXMediaSequence { seq_num })
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let seq_num = tag(input, Self::PREFIX)?.parse()?;
+
+        Ok(ExtXMediaSequence::new(seq_num))
     }
 }
 
diff --git a/src/tags/media_playlist/playlist_type.rs b/src/tags/media_playlist/playlist_type.rs
index 16d9672..f9911b7 100644
--- a/src/tags/media_playlist/playlist_type.rs
+++ b/src/tags/media_playlist/playlist_type.rs
@@ -1,8 +1,9 @@
-use crate::types::{PlaylistType, ProtocolVersion};
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
-use trackable::error::ErrorKindExt;
+
+use crate::types::{PlaylistType, ProtocolVersion};
+use crate::utils::tag;
+use crate::Error;
 
 /// [4.3.3.5. EXT-X-PLAYLIST-TYPE]
 ///
@@ -40,10 +41,10 @@ impl fmt::Display for ExtXPlaylistType {
 impl FromStr for ExtXPlaylistType {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let playlist_type = may_invalid!(s.split_at(Self::PREFIX.len()).1.parse())?;
-        Ok(ExtXPlaylistType { playlist_type })
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?.parse()?;
+
+        Ok(ExtXPlaylistType::new(input))
     }
 }
 
diff --git a/src/tags/media_playlist/target_duration.rs b/src/tags/media_playlist/target_duration.rs
index 2f759b9..32ca2a9 100644
--- a/src/tags/media_playlist/target_duration.rs
+++ b/src/tags/media_playlist/target_duration.rs
@@ -1,9 +1,10 @@
-use crate::types::ProtocolVersion;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 use std::time::Duration;
-use trackable::error::ErrorKindExt;
+
+use crate::types::ProtocolVersion;
+use crate::utils::tag;
+use crate::Error;
 
 /// [4.3.3.1. EXT-X-TARGETDURATION]
 ///
@@ -43,11 +44,11 @@ impl fmt::Display for ExtXTargetDuration {
 
 impl FromStr for ExtXTargetDuration {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let duration = may_invalid!(s.split_at(Self::PREFIX.len()).1.parse())?;
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?.parse()?;
         Ok(ExtXTargetDuration {
-            duration: Duration::from_secs(duration),
+            duration: Duration::from_secs(input),
         })
     }
 }
diff --git a/src/tags/media_segment/byte_range.rs b/src/tags/media_segment/byte_range.rs
index 9afddfa..e7a895a 100644
--- a/src/tags/media_segment/byte_range.rs
+++ b/src/tags/media_segment/byte_range.rs
@@ -2,10 +2,9 @@ use std::fmt;
 use std::ops::Deref;
 use std::str::FromStr;
 
-use trackable::error::ErrorKindExt;
-
 use crate::types::{ByteRange, ProtocolVersion};
-use crate::{Error, ErrorKind, Result};
+use crate::utils::tag;
+use crate::Error;
 
 /// [4.3.2.2. EXT-X-BYTERANGE]
 ///
@@ -73,26 +72,20 @@ impl fmt::Display for ExtXByteRange {
 impl FromStr for ExtXByteRange {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        // check if the string starts with the PREFIX
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let byte_range = s.split_at(Self::PREFIX.len()).1;
-        let tokens = byte_range.splitn(2, '@').collect::<Vec<_>>();
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
+
+        let tokens = input.splitn(2, '@').collect::<Vec<_>>();
         if tokens.is_empty() {
-            Err(ErrorKind::InvalidInput)?;
+            return Err(Error::invalid_input());
         }
 
-        let length = tokens[0]
-            .parse()
-            .map_err(|e| ErrorKind::InvalidInput.cause(e))?;
+        let length = tokens[0].parse()?;
+
         let start = {
             let mut result = None;
             if tokens.len() == 2 {
-                result = Some(
-                    tokens[1]
-                        .parse()
-                        .map_err(|e| ErrorKind::InvalidInput.cause(e))?,
-                );
+                result = Some(tokens[1].parse()?);
             }
             result
         };
diff --git a/src/tags/media_segment/date_range.rs b/src/tags/media_segment/date_range.rs
index dae13ce..8fa6f11 100644
--- a/src/tags/media_segment/date_range.rs
+++ b/src/tags/media_segment/date_range.rs
@@ -1,12 +1,13 @@
-use crate::attribute::AttributePairs;
-use crate::types::{DecimalFloatingPoint, ProtocolVersion};
-use crate::utils::{quote, unquote};
-use crate::{Error, ErrorKind, Result};
 use std::collections::BTreeMap;
 use std::fmt;
 use std::str::FromStr;
 use std::time::Duration;
 
+use crate::attribute::AttributePairs;
+use crate::types::{DecimalFloatingPoint, ProtocolVersion};
+use crate::utils::{quote, tag, unquote};
+use crate::Error;
+
 /// [4.3.2.7.  EXT-X-DATERANGE]
 ///
 /// [4.3.2.7.  EXT-X-DATERANGE]: https://tools.ietf.org/html/rfc8216#section-4.3.2.7
@@ -79,8 +80,9 @@ impl fmt::Display for ExtXDateRange {
 
 impl FromStr for ExtXDateRange {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
 
         let mut id = None;
         let mut class = None;
@@ -92,28 +94,32 @@ impl FromStr for ExtXDateRange {
         let mut scte35_out = None;
         let mut scte35_in = None;
         let mut end_on_next = false;
+
         let mut client_attributes = BTreeMap::new();
-        let attrs = AttributePairs::parse(s.split_at(Self::PREFIX.len()).1);
+        let attrs = AttributePairs::parse(input);
+
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = attr?;
             match key {
                 "ID" => id = Some(unquote(value)),
                 "CLASS" => class = Some(unquote(value)),
                 "START-DATE" => start_date = Some(unquote(value)),
                 "END-DATE" => end_date = Some(unquote(value)),
                 "DURATION" => {
-                    let seconds: DecimalFloatingPoint = track!(value.parse())?;
+                    let seconds: DecimalFloatingPoint = (value.parse())?;
                     duration = Some(seconds.to_duration());
                 }
                 "PLANNED-DURATION" => {
-                    let seconds: DecimalFloatingPoint = track!(value.parse())?;
+                    let seconds: DecimalFloatingPoint = (value.parse())?;
                     planned_duration = Some(seconds.to_duration());
                 }
                 "SCTE35-CMD" => scte35_cmd = Some(unquote(value)),
                 "SCTE35-OUT" => scte35_out = Some(unquote(value)),
                 "SCTE35-IN" => scte35_in = Some(unquote(value)),
                 "END-ON-NEXT" => {
-                    track_assert_eq!(value, "YES", ErrorKind::InvalidInput);
+                    if value != "YES" {
+                        return Err(Error::invalid_input());
+                    }
                     end_on_next = true;
                 }
                 _ => {
@@ -127,10 +133,12 @@ impl FromStr for ExtXDateRange {
             }
         }
 
-        let id = track_assert_some!(id, ErrorKind::InvalidInput);
-        let start_date = track_assert_some!(start_date, ErrorKind::InvalidInput);
+        let id = id.ok_or(Error::missing_value("EXT-X-ID"))?;
+        let start_date = start_date.ok_or(Error::missing_value("EXT-X-START-DATE"))?;
         if end_on_next {
-            track_assert!(class.is_some(), ErrorKind::InvalidInput);
+            if class.is_none() {
+                return Err(Error::invalid_input());
+            }
         }
         Ok(ExtXDateRange {
             id,
diff --git a/src/tags/media_segment/inf.rs b/src/tags/media_segment/inf.rs
index ac215af..ddf305c 100644
--- a/src/tags/media_segment/inf.rs
+++ b/src/tags/media_segment/inf.rs
@@ -1,9 +1,10 @@
-use crate::types::{DecimalFloatingPoint, ProtocolVersion, SingleLineString};
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 use std::time::Duration;
-use trackable::error::ErrorKindExt;
+
+use crate::types::{DecimalFloatingPoint, ProtocolVersion, SingleLineString};
+use crate::utils::tag;
+use crate::Error;
 
 /// [4.3.2.1. EXTINF]
 ///
@@ -70,18 +71,20 @@ impl fmt::Display for ExtInf {
 
 impl FromStr for ExtInf {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let mut tokens = s.split_at(Self::PREFIX.len()).1.splitn(2, ',');
 
-        let seconds: DecimalFloatingPoint =
-            may_invalid!(tokens.next().expect("Never fails").parse())?;
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
+        let mut tokens = input.splitn(2, ',');
+
+        let seconds: DecimalFloatingPoint = tokens.next().expect("Never fails").parse()?;
         let duration = seconds.to_duration();
 
-        let title = if let Some(title) = tokens.next() {
-            Some(track!(SingleLineString::new(title))?)
-        } else {
-            None
+        let title = {
+            if let Some(title) = tokens.next() {
+                Some((SingleLineString::new(title))?)
+            } else {
+                None
+            }
         };
         Ok(ExtInf { duration, title })
     }
diff --git a/src/tags/media_segment/key.rs b/src/tags/media_segment/key.rs
index e9dda27..fb47c83 100644
--- a/src/tags/media_segment/key.rs
+++ b/src/tags/media_segment/key.rs
@@ -1,9 +1,11 @@
-use crate::attribute::AttributePairs;
-use crate::types::{DecryptionKey, ProtocolVersion};
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::attribute::AttributePairs;
+use crate::types::{DecryptionKey, ProtocolVersion};
+use crate::utils::tag;
+use crate::Error;
+
 /// [4.3.2.4. EXT-X-KEY]
 ///
 /// [4.3.2.4. EXT-X-KEY]: https://tools.ietf.org/html/rfc8216#section-4.3.2.4
@@ -55,21 +57,19 @@ impl fmt::Display for ExtXKey {
 impl FromStr for ExtXKey {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let suffix = s.split_at(Self::PREFIX.len()).1;
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
 
-        if AttributePairs::parse(suffix).any(|a| a.as_ref().ok() == Some(&("METHOD", "NONE"))) {
-            for attr in AttributePairs::parse(suffix) {
-                let (key, _) = track!(attr)?;
-                track_assert_ne!(key, "URI", ErrorKind::InvalidInput);
-                track_assert_ne!(key, "IV", ErrorKind::InvalidInput);
-                track_assert_ne!(key, "KEYFORMAT", ErrorKind::InvalidInput);
-                track_assert_ne!(key, "KEYFORMATVERSIONS", ErrorKind::InvalidInput);
+        if AttributePairs::parse(input).any(|a| a.as_ref().ok() == Some(&("METHOD", "NONE"))) {
+            for attr in AttributePairs::parse(input) {
+                let (key, _) = attr?;
+                if key == "URI" || key == "IV" || key == "KEYFORMAT" || key == "KEYFORMATVERSIONS" {
+                    return Err(Error::invalid_input());
+                }
             }
             Ok(ExtXKey { key: None })
         } else {
-            let key = track!(suffix.parse())?;
+            let key = input.parse()?;
             Ok(ExtXKey { key: Some(key) })
         }
     }
diff --git a/src/tags/media_segment/map.rs b/src/tags/media_segment/map.rs
index 1ef468b..728afa4 100644
--- a/src/tags/media_segment/map.rs
+++ b/src/tags/media_segment/map.rs
@@ -1,10 +1,11 @@
-use crate::attribute::AttributePairs;
-use crate::types::{ByteRange, ProtocolVersion};
-use crate::utils::{quote, unquote};
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::attribute::AttributePairs;
+use crate::types::{ByteRange, ProtocolVersion};
+use crate::utils::{quote, tag, unquote};
+use crate::Error;
+
 /// [4.3.2.5. EXT-X-MAP]
 ///
 /// [4.3.2.5. EXT-X-MAP]: https://tools.ietf.org/html/rfc8216#section-4.3.2.5
@@ -63,18 +64,18 @@ impl fmt::Display for ExtXMap {
 impl FromStr for ExtXMap {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
 
         let mut uri = None;
         let mut range = None;
-        let attrs = AttributePairs::parse(s.split_at(Self::PREFIX.len()).1);
+        let attrs = AttributePairs::parse(input);
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = (attr)?;
             match key {
                 "URI" => uri = Some(unquote(value)),
                 "BYTERANGE" => {
-                    range = Some(track!(unquote(value).parse())?);
+                    range = Some((unquote(value).parse())?);
                 }
                 _ => {
                     // [6.3.1. General Client Responsibilities]
@@ -83,7 +84,7 @@ impl FromStr for ExtXMap {
             }
         }
 
-        let uri = track_assert_some!(uri, ErrorKind::InvalidInput);
+        let uri = uri.ok_or(Error::missing_value("EXT-X-URI"))?;
         Ok(ExtXMap { uri, range })
     }
 }
@@ -102,7 +103,8 @@ mod test {
 
         let tag = ExtXMap::with_range("foo", ByteRange::new(9, Some(2)));
         let text = r#"#EXT-X-MAP:URI="foo",BYTERANGE="9@2""#;
-        track_try_unwrap!(ExtXMap::from_str(text));
+        ExtXMap::from_str(text).unwrap();
+
         assert_eq!(text.parse().ok(), Some(tag.clone()));
         assert_eq!(tag.to_string(), text);
         assert_eq!(tag.requires_version(), ProtocolVersion::V6);
diff --git a/src/tags/media_segment/program_date_time.rs b/src/tags/media_segment/program_date_time.rs
index 625fdeb..a4be50d 100644
--- a/src/tags/media_segment/program_date_time.rs
+++ b/src/tags/media_segment/program_date_time.rs
@@ -1,8 +1,10 @@
-use crate::types::{ProtocolVersion, SingleLineString};
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::types::{ProtocolVersion, SingleLineString};
+use crate::utils::tag;
+use crate::Error;
+
 /// [4.3.2.6. EXT-X-PROGRAM-DATE-TIME]
 ///
 /// [4.3.2.6. EXT-X-PROGRAM-DATE-TIME]: https://tools.ietf.org/html/rfc8216#section-4.3.2.6
@@ -39,11 +41,13 @@ impl fmt::Display for ExtXProgramDateTime {
 impl FromStr for ExtXProgramDateTime {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
-        let suffix = s.split_at(Self::PREFIX.len()).1;
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
+
+        // TODO: parse with chrono
+
         Ok(ExtXProgramDateTime {
-            date_time: track!(SingleLineString::new(suffix))?,
+            date_time: (SingleLineString::new(input))?,
         })
     }
 }
diff --git a/src/tags/mod.rs b/src/tags/mod.rs
index b4a72fa..ebad0b7 100644
--- a/src/tags/mod.rs
+++ b/src/tags/mod.rs
@@ -2,12 +2,6 @@
 //!
 //! [4.3. Playlist Tags]: https://tools.ietf.org/html/rfc8216#section-4.3
 
-macro_rules! may_invalid {
-    ($expr:expr) => {
-        $expr.map_err(|e| track!(Error::from(ErrorKind::InvalidInput.cause(e))))
-    };
-}
-
 macro_rules! impl_from {
     ($to:ident, $from:ident) => {
         impl From<$from> for $to {
diff --git a/src/tags/shared/independent_segments.rs b/src/tags/shared/independent_segments.rs
index 2aa3e82..5268dcd 100644
--- a/src/tags/shared/independent_segments.rs
+++ b/src/tags/shared/independent_segments.rs
@@ -1,8 +1,10 @@
-use crate::types::ProtocolVersion;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::types::ProtocolVersion;
+use crate::utils::tag;
+use crate::Error;
+
 /// [4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS]
 ///
 /// [4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS]: https://tools.ietf.org/html/rfc8216#section-4.3.5.1
@@ -26,8 +28,8 @@ impl fmt::Display for ExtXIndependentSegments {
 impl FromStr for ExtXIndependentSegments {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert_eq!(s, Self::PREFIX, ErrorKind::InvalidInput);
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        tag(input, Self::PREFIX)?;
         Ok(ExtXIndependentSegments)
     }
 }
diff --git a/src/tags/shared/start.rs b/src/tags/shared/start.rs
index 560b144..f946992 100644
--- a/src/tags/shared/start.rs
+++ b/src/tags/shared/start.rs
@@ -1,10 +1,11 @@
-use crate::attribute::AttributePairs;
-use crate::types::{ProtocolVersion, SignedDecimalFloatingPoint};
-use crate::utils::parse_yes_or_no;
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::FromStr;
 
+use crate::attribute::AttributePairs;
+use crate::types::{ProtocolVersion, SignedDecimalFloatingPoint};
+use crate::utils::{parse_yes_or_no, tag};
+use crate::Error;
+
 /// [4.3.5.2. EXT-X-START]
 ///
 /// [4.3.5.2. EXT-X-START]: https://tools.ietf.org/html/rfc8216#section-4.3.5.2
@@ -64,17 +65,19 @@ impl fmt::Display for ExtXStart {
 impl FromStr for ExtXStart {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(s.starts_with(Self::PREFIX), ErrorKind::InvalidInput);
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let input = tag(input, Self::PREFIX)?;
 
         let mut time_offset = None;
         let mut precise = false;
-        let attrs = AttributePairs::parse(s.split_at(Self::PREFIX.len()).1);
+
+        let attrs = AttributePairs::parse(input);
+
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = (attr)?;
             match key {
-                "TIME-OFFSET" => time_offset = Some(track!(value.parse())?),
-                "PRECISE" => precise = track!(parse_yes_or_no(value))?,
+                "TIME-OFFSET" => time_offset = Some((value.parse())?),
+                "PRECISE" => precise = (parse_yes_or_no(value))?,
                 _ => {
                     // [6.3.1. General Client Responsibilities]
                     // > ignore any attribute/value pair with an unrecognized AttributeName.
@@ -82,7 +85,8 @@ impl FromStr for ExtXStart {
             }
         }
 
-        let time_offset = track_assert_some!(time_offset, ErrorKind::InvalidInput);
+        let time_offset = time_offset.ok_or(Error::missing_value("EXT-X-TIME-OFFSET"))?;
+
         Ok(ExtXStart {
             time_offset,
             precise,
diff --git a/src/types/byte_range.rs b/src/types/byte_range.rs
index 443ab53..09f3535 100644
--- a/src/types/byte_range.rs
+++ b/src/types/byte_range.rs
@@ -1,10 +1,9 @@
 use std::fmt;
-use std::str::{self, FromStr};
+use std::str::FromStr;
 
 use getset::{Getters, MutGetters, Setters};
-use trackable::error::ErrorKindExt;
 
-use crate::{Error, ErrorKind, Result};
+use crate::Error;
 
 /// Byte range.
 ///
@@ -42,23 +41,18 @@ impl fmt::Display for ByteRange {
 impl FromStr for ByteRange {
     type Err = Error;
 
-    fn from_str(s: &str) -> Result<Self> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let tokens = s.splitn(2, '@').collect::<Vec<_>>();
         if tokens.is_empty() {
-            Err(ErrorKind::InvalidInput)?;
+            return Err(Error::invalid_input());
         }
 
-        let length = tokens[0]
-            .parse()
-            .map_err(|e| ErrorKind::InvalidInput.cause(e))?;
+        let length = tokens[0].parse()?;
+
         let start = {
             let mut result = None;
             if tokens.len() == 2 {
-                result = Some(
-                    tokens[1]
-                        .parse()
-                        .map_err(|e| ErrorKind::InvalidInput.cause(e))?,
-                );
+                result = Some(tokens[1].parse()?);
             }
             result
         };
diff --git a/src/types/decimal_floating_point.rs b/src/types/decimal_floating_point.rs
index aa555e9..b044cc4 100644
--- a/src/types/decimal_floating_point.rs
+++ b/src/types/decimal_floating_point.rs
@@ -1,8 +1,8 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
-use std::str::{self, FromStr};
+use std::str::FromStr;
 use std::time::Duration;
-use trackable::error::ErrorKindExt;
+
+use crate::Error;
 
 /// Non-negative decimal floating-point number.
 ///
@@ -19,9 +19,10 @@ impl DecimalFloatingPoint {
     ///
     /// The given value must have a positive sign and be finite,
     /// otherwise this function will return an error that has the kind `ErrorKind::InvalidInput`.
-    pub fn new(n: f64) -> Result<Self> {
-        track_assert!(n.is_sign_positive(), ErrorKind::InvalidInput);
-        track_assert!(n.is_finite(), ErrorKind::InvalidInput);
+    pub fn new(n: f64) -> crate::Result<Self> {
+        if !n.is_sign_positive() || !n.is_finite() {
+            return Err(Error::invalid_input());
+        }
         Ok(DecimalFloatingPoint(n))
     }
 
@@ -59,12 +60,12 @@ impl fmt::Display for DecimalFloatingPoint {
 
 impl FromStr for DecimalFloatingPoint {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(
-            s.chars().all(|c| c.is_digit(10) || c == '.'),
-            ErrorKind::InvalidInput
-        );
-        let n = track!(s.parse().map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        if !input.chars().all(|c| c.is_digit(10) || c == '.') {
+            return Err(Error::invalid_input());
+        }
+        let n = input.parse()?;
         Ok(DecimalFloatingPoint(n))
     }
 }
diff --git a/src/types/decimal_resolution.rs b/src/types/decimal_resolution.rs
index f323577..67128ff 100644
--- a/src/types/decimal_resolution.rs
+++ b/src/types/decimal_resolution.rs
@@ -1,7 +1,7 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::{self, FromStr};
-use trackable::error::ErrorKindExt;
+
+use crate::Error;
 
 /// Decimal resolution.
 ///
@@ -25,13 +25,15 @@ impl fmt::Display for DecimalResolution {
 
 impl FromStr for DecimalResolution {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        let mut tokens = s.splitn(2, 'x');
-        let width = tokens.next().expect("Never fails");
-        let height = track_assert_some!(tokens.next(), ErrorKind::InvalidInput);
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let mut tokens = input.splitn(2, 'x');
+        let width = tokens.next().ok_or(Error::missing_value("width"))?;
+        let height = tokens.next().ok_or(Error::missing_value("height"))?;
+
         Ok(DecimalResolution {
-            width: track!(width.parse().map_err(|e| ErrorKind::InvalidInput.cause(e)))?,
-            height: track!(height.parse().map_err(|e| ErrorKind::InvalidInput.cause(e)))?,
+            width: width.parse().map_err(|e| Error::custom(e))?,
+            height: height.parse().map_err(|e| Error::custom(e))?,
         })
     }
 }
diff --git a/src/types/decryption_key.rs b/src/types/decryption_key.rs
index 15a6f35..87c7116 100644
--- a/src/types/decryption_key.rs
+++ b/src/types/decryption_key.rs
@@ -1,9 +1,10 @@
+use std::fmt;
+use std::str::{self, FromStr};
+
 use crate::attribute::AttributePairs;
 use crate::types::{EncryptionMethod, InitializationVector, ProtocolVersion};
 use crate::utils::{quote, unquote};
-use crate::{Error, ErrorKind, Result};
-use std::fmt;
-use std::str::{self, FromStr};
+use crate::Error;
 
 /// Decryption key.
 ///
@@ -51,19 +52,21 @@ impl fmt::Display for DecryptionKey {
 
 impl FromStr for DecryptionKey {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
         let mut method = None;
         let mut uri = None;
         let mut iv = None;
         let mut key_format = None;
         let mut key_format_versions = None;
-        let attrs = AttributePairs::parse(s);
+
+        let attrs = AttributePairs::parse(input);
         for attr in attrs {
-            let (key, value) = track!(attr)?;
+            let (key, value) = (attr)?;
             match key {
-                "METHOD" => method = Some(track!(value.parse())?),
+                "METHOD" => method = Some((value.parse())?),
                 "URI" => uri = Some(unquote(value)),
-                "IV" => iv = Some(track!(value.parse())?),
+                "IV" => iv = Some((value.parse())?),
                 "KEYFORMAT" => key_format = Some(unquote(value)),
                 "KEYFORMATVERSIONS" => key_format_versions = Some(unquote(value)),
                 _ => {
@@ -72,8 +75,10 @@ impl FromStr for DecryptionKey {
                 }
             }
         }
-        let method = track_assert_some!(method, ErrorKind::InvalidInput);
-        let uri = track_assert_some!(uri, ErrorKind::InvalidInput);
+
+        let method = method.ok_or(Error::missing_value("EXT-X-METHOD"))?;
+        let uri = uri.ok_or(Error::missing_value("EXT-X-URI"))?;
+
         Ok(DecryptionKey {
             method,
             uri,
diff --git a/src/types/encryption_method.rs b/src/types/encryption_method.rs
index 971e7bb..379e251 100644
--- a/src/types/encryption_method.rs
+++ b/src/types/encryption_method.rs
@@ -1,6 +1,7 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
-use std::str::{self, FromStr};
+use std::str::FromStr;
+
+use crate::Error;
 
 /// Encryption method.
 ///
@@ -25,15 +26,15 @@ impl fmt::Display for EncryptionMethod {
 
 impl FromStr for EncryptionMethod {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        match s {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        match input {
             "AES-128" => Ok(EncryptionMethod::Aes128),
             "SAMPLE-AES" => Ok(EncryptionMethod::SampleAes),
-            _ => track_panic!(
-                ErrorKind::InvalidInput,
+            _ => Err(Error::custom(format!(
                 "Unknown encryption method: {:?}",
-                s
-            ),
+                input
+            ))),
         }
     }
 }
diff --git a/src/types/hdcp_level.rs b/src/types/hdcp_level.rs
index 436178f..fc67f9e 100644
--- a/src/types/hdcp_level.rs
+++ b/src/types/hdcp_level.rs
@@ -1,6 +1,7 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
-use std::str::{self, FromStr};
+use std::str::FromStr;
+
+use crate::Error;
 
 /// HDCP level.
 ///
@@ -25,11 +26,12 @@ impl fmt::Display for HdcpLevel {
 
 impl FromStr for HdcpLevel {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        match s {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        match input {
             "TYPE-0" => Ok(HdcpLevel::Type0),
             "NONE" => Ok(HdcpLevel::None),
-            _ => track_panic!(ErrorKind::InvalidInput, "Unknown HDCP level: {:?}", s),
+            _ => Err(Error::custom(format!("Unknown HDCP level: {:?}", input))),
         }
     }
 }
diff --git a/src/types/hexadecimal_sequence.rs b/src/types/hexadecimal_sequence.rs
index 930adca..fd6d69e 100644
--- a/src/types/hexadecimal_sequence.rs
+++ b/src/types/hexadecimal_sequence.rs
@@ -1,8 +1,8 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::ops::Deref;
-use std::str::{self, FromStr};
-use trackable::error::ErrorKindExt;
+use std::str::FromStr;
+
+use crate::Error;
 
 /// Hexadecimal sequence.
 ///
@@ -49,20 +49,24 @@ impl fmt::Display for HexadecimalSequence {
 
 impl FromStr for HexadecimalSequence {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(
-            s.starts_with("0x") || s.starts_with("0X"),
-            ErrorKind::InvalidInput
-        );
-        track_assert!(s.len() % 2 == 0, ErrorKind::InvalidInput);
 
-        let mut v = Vec::with_capacity(s.len() / 2 - 1);
-        for c in s.as_bytes().chunks(2).skip(1) {
-            let d = track!(str::from_utf8(c).map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
-            let b =
-                track!(u8::from_str_radix(d, 16).map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
-            v.push(b);
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        if !(input.starts_with("0x") || input.starts_with("0X")) {
+            return Err(Error::invalid_input());
         }
-        Ok(HexadecimalSequence(v))
+
+        if input.len() % 2 != 0 {
+            return Err(Error::invalid_input());
+        }
+
+        let mut result = Vec::with_capacity(input.len() / 2 - 1);
+
+        for c in input.as_bytes().chunks(2).skip(1) {
+            let d = String::from_utf8(c.to_vec()).map_err(|e| Error::custom(e))?;
+            let b = u8::from_str_radix(d.as_str(), 16)?;
+            result.push(b);
+        }
+
+        Ok(HexadecimalSequence(result))
     }
 }
diff --git a/src/types/in_stream_id.rs b/src/types/in_stream_id.rs
index 8b4aa56..cdff1f5 100644
--- a/src/types/in_stream_id.rs
+++ b/src/types/in_stream_id.rs
@@ -1,6 +1,7 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
-use std::str::{self, FromStr};
+use std::str::FromStr;
+
+use crate::Error;
 
 /// Identifier of a rendition within the segments in a media playlist.
 ///
@@ -87,8 +88,9 @@ impl fmt::Display for InStreamId {
 
 impl FromStr for InStreamId {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        Ok(match s {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        Ok(match input {
             "CC1" => InStreamId::Cc1,
             "CC2" => InStreamId::Cc2,
             "CC3" => InStreamId::Cc3,
@@ -156,7 +158,7 @@ impl FromStr for InStreamId {
             "SERVICE61" => InStreamId::Service61,
             "SERVICE62" => InStreamId::Service62,
             "SERVICE63" => InStreamId::Service63,
-            _ => track_panic!(ErrorKind::InvalidInput, "Unknown instream id: {:?}", s),
+            _ => return Err(Error::custom(format!("Unknown instream id: {:?}", input))),
         })
     }
 }
diff --git a/src/types/initialization_vector.rs b/src/types/initialization_vector.rs
index 9cb64fe..9743f34 100644
--- a/src/types/initialization_vector.rs
+++ b/src/types/initialization_vector.rs
@@ -1,8 +1,8 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::ops::Deref;
 use std::str::{self, FromStr};
-use trackable::error::ErrorKindExt;
+
+use crate::Error;
 
 /// Initialization vector.
 ///
@@ -37,20 +37,22 @@ impl fmt::Display for InitializationVector {
 
 impl FromStr for InitializationVector {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(
-            s.starts_with("0x") || s.starts_with("0X"),
-            ErrorKind::InvalidInput
-        );
-        track_assert_eq!(s.len() - 2, 32, ErrorKind::InvalidInput);
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if !(s.starts_with("0x") || s.starts_with("0X")) {
+            return Err(Error::invalid_input());
+        }
+        if s.len() - 2 != 32 {
+            return Err(Error::invalid_input());
+        }
 
         let mut v = [0; 16];
         for (i, c) in s.as_bytes().chunks(2).skip(1).enumerate() {
-            let d = track!(str::from_utf8(c).map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
-            let b =
-                track!(u8::from_str_radix(d, 16).map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
+            let d = str::from_utf8(c).map_err(|e| Error::custom(e))?;
+            let b = u8::from_str_radix(d, 16).map_err(|e| Error::custom(e))?;
             v[i] = b;
         }
+
         Ok(InitializationVector(v))
     }
 }
diff --git a/src/types/media_type.rs b/src/types/media_type.rs
index 103abde..f47b7d3 100644
--- a/src/types/media_type.rs
+++ b/src/types/media_type.rs
@@ -1,7 +1,8 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::{self, FromStr};
 
+use crate::Error;
+
 /// Media type.
 ///
 /// See: [4.3.4.1. EXT-X-MEDIA]
@@ -29,13 +30,16 @@ impl fmt::Display for MediaType {
 
 impl FromStr for MediaType {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        Ok(match s {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        Ok(match input {
             "AUDIO" => MediaType::Audio,
             "VIDEO" => MediaType::Video,
             "SUBTITLES" => MediaType::Subtitles,
             "CLOSED-CAPTIONS" => MediaType::ClosedCaptions,
-            _ => track_panic!(ErrorKind::InvalidInput, "Unknown media type: {:?}", s),
+            _ => {
+                return Err(Error::invalid_input());
+            }
         })
     }
 }
diff --git a/src/types/playlist_type.rs b/src/types/playlist_type.rs
index e9dbb00..29efa54 100644
--- a/src/types/playlist_type.rs
+++ b/src/types/playlist_type.rs
@@ -1,6 +1,7 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
-use std::str::{self, FromStr};
+use std::str::FromStr;
+
+use crate::Error;
 
 /// Playlist type.
 ///
@@ -25,11 +26,12 @@ impl fmt::Display for PlaylistType {
 
 impl FromStr for PlaylistType {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        match s {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        match input {
             "EVENT" => Ok(PlaylistType::Event),
             "VOD" => Ok(PlaylistType::Vod),
-            _ => track_panic!(ErrorKind::InvalidInput, "Unknown playlist type: {:?}", s),
+            _ => Err(Error::custom(format!("Unknown playlist type: {:?}", input))),
         }
     }
 }
diff --git a/src/types/protocol_version.rs b/src/types/protocol_version.rs
index 312707b..626e13e 100644
--- a/src/types/protocol_version.rs
+++ b/src/types/protocol_version.rs
@@ -1,7 +1,8 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::{self, FromStr};
 
+use crate::Error;
+
 /// [7. Protocol Version Compatibility]
 ///
 /// [7. Protocol Version Compatibility]: https://tools.ietf.org/html/rfc8216#section-7
@@ -32,8 +33,9 @@ impl fmt::Display for ProtocolVersion {
 }
 impl FromStr for ProtocolVersion {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        Ok(match s {
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        Ok(match input {
             "1" => ProtocolVersion::V1,
             "2" => ProtocolVersion::V2,
             "3" => ProtocolVersion::V3,
@@ -41,7 +43,7 @@ impl FromStr for ProtocolVersion {
             "5" => ProtocolVersion::V5,
             "6" => ProtocolVersion::V6,
             "7" => ProtocolVersion::V7,
-            _ => track_panic!(ErrorKind::InvalidInput, "Unknown protocol version: {:?}", s),
+            _ => return Err(Error::unknown_protocol_version(input)),
         })
     }
 }
diff --git a/src/types/signed_decimal_floating_point.rs b/src/types/signed_decimal_floating_point.rs
index 999d0a2..0c3691c 100644
--- a/src/types/signed_decimal_floating_point.rs
+++ b/src/types/signed_decimal_floating_point.rs
@@ -1,7 +1,7 @@
-use crate::{Error, ErrorKind, Result};
 use std::fmt;
 use std::str::{self, FromStr};
-use trackable::error::ErrorKindExt;
+
+use crate::Error;
 
 /// Signed decimal floating-point number.
 ///
@@ -18,9 +18,12 @@ impl SignedDecimalFloatingPoint {
     ///
     /// The given value must be finite,
     /// otherwise this function will return an error that has the kind `ErrorKind::InvalidInput`.
-    pub fn new(n: f64) -> Result<Self> {
-        track_assert!(n.is_finite(), ErrorKind::InvalidInput);
-        Ok(SignedDecimalFloatingPoint(n))
+    pub fn new(n: f64) -> crate::Result<Self> {
+        if !n.is_finite() {
+            Err(Error::invalid_input())
+        } else {
+            Ok(SignedDecimalFloatingPoint(n))
+        }
     }
 
     /// Converts `DecimalFloatingPoint` to `f64`.
@@ -45,12 +48,8 @@ impl fmt::Display for SignedDecimalFloatingPoint {
 
 impl FromStr for SignedDecimalFloatingPoint {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Self> {
-        track_assert!(
-            s.chars().all(|c| c.is_digit(10) || c == '.' || c == '-'),
-            ErrorKind::InvalidInput
-        );
-        let n = track!(s.parse().map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
-        Ok(SignedDecimalFloatingPoint(n))
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        SignedDecimalFloatingPoint::new(input.parse().map_err(Error::parse_float_error)?)
     }
 }
diff --git a/src/types/single_line_string.rs b/src/types/single_line_string.rs
index 3f99d35..fea3dbb 100644
--- a/src/types/single_line_string.rs
+++ b/src/types/single_line_string.rs
@@ -1,4 +1,4 @@
-use crate::{ErrorKind, Result};
+use crate::Error;
 use std::fmt;
 use std::ops::Deref;
 
@@ -17,10 +17,13 @@ impl SingleLineString {
     ///
     /// If the given string contains any control characters,
     /// this function will return an error which has the kind `ErrorKind::InvalidInput`.
-    pub fn new<T: Into<String>>(s: T) -> Result<Self> {
+    pub fn new<T: Into<String>>(s: T) -> crate::Result<Self> {
         let s = s.into();
-        track_assert!(!s.chars().any(|c| c.is_control()), ErrorKind::InvalidInput);
-        Ok(SingleLineString(s))
+        if s.chars().any(|c| c.is_control()) {
+            Err(Error::invalid_input())
+        } else {
+            Ok(SingleLineString(s))
+        }
     }
 }
 
diff --git a/src/utils.rs b/src/utils.rs
index 946dab9..7f557ec 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -1,23 +1,15 @@
-use crate::{ErrorKind, Result};
-use trackable::error::ErrorKindExt;
+use crate::{Error, Result};
 
 pub(crate) fn parse_yes_or_no<T: AsRef<str>>(s: T) -> Result<bool> {
     match s.as_ref() {
         "YES" => Ok(true),
         "NO" => Ok(false),
-        _ => track_panic!(
-            ErrorKind::InvalidInput,
-            "Unexpected value: {:?}",
-            s.as_ref()
-        ),
+        _ => Err(Error::invalid_input()),
     }
 }
 
 pub(crate) fn parse_u64<T: AsRef<str>>(s: T) -> Result<u64> {
-    let n = track!(s
-        .as_ref()
-        .parse()
-        .map_err(|e| ErrorKind::InvalidInput.cause(e)))?;
+    let n = s.as_ref().parse().map_err(Error::unknown)?; // TODO: Error::number
     Ok(n)
 }
 
@@ -45,13 +37,17 @@ pub(crate) fn quote<T: ToString>(value: T) -> String {
 }
 
 /// Checks, if the given tag is at the start of the input. If this is the case, it will remove it
-/// return the rest of the input, otherwise it will return an error.
+/// and return the rest of the input.
+///
+/// # Error
+/// This function will return `Error::MissingTag`, if the input doesn't start with the tag, that
+/// has been passed to this function.
 pub(crate) fn tag<T>(input: &str, tag: T) -> crate::Result<&str>
 where
     T: AsRef<str>,
 {
     if !input.starts_with(tag.as_ref()) {
-        Err(ErrorKind::InvalidInput)?; // TODO!
+        return Err(Error::missing_tag(tag.as_ref(), input));
     }
     let result = input.split_at(tag.as_ref().len()).1;
     Ok(result)