From d4430ecc6ab9efa3195f2c2b3a5d6239ef07ba32 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Fri, 20 May 2022 16:58:46 +0300
Subject: [PATCH] Implement more iterator functions / traits in custom
 iterators for efficiency reasons

---
 gstreamer-audio/src/audio_format.rs           |  45 +++-
 .../src/discoverer_stream_info.rs             |   2 +
 gstreamer-sdp/src/sdp_media.rs                |  53 ++++-
 gstreamer-sdp/src/sdp_message.rs              | 109 +++++++--
 gstreamer-video/src/video_format.rs           |  37 +++
 gstreamer-video/src/video_meta.rs             |  24 +-
 .../src/video_overlay_composition.rs          |  54 ++++-
 gstreamer/src/buffer.rs                       |  66 +++++-
 gstreamer/src/bufferlist.rs                   |  51 +++-
 gstreamer/src/caps.rs                         |  58 ++++-
 gstreamer/src/caps_features.rs                |  82 +++++--
 gstreamer/src/iterator.rs                     |   2 +
 gstreamer/src/stream_collection.rs            |  54 ++++-
 gstreamer/src/structure.rs                    |  69 +++---
 gstreamer/src/tags.rs                         | 219 ++++++++++++++----
 15 files changed, 739 insertions(+), 186 deletions(-)

diff --git a/gstreamer-audio/src/audio_format.rs b/gstreamer-audio/src/audio_format.rs
index 5212814f4..8566418fc 100644
--- a/gstreamer-audio/src/audio_format.rs
+++ b/gstreamer-audio/src/audio_format.rs
@@ -255,25 +255,58 @@ impl Iterator for AudioFormatIterator {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.len {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.len - self.idx) as usize;
+        let remaining = self.len - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.len - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.len || overflow {
+            self.idx = self.len;
+            None
+        } else {
+            self.idx = end + 1;
+            Some(AUDIO_FORMATS_ALL[end])
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.len {
+            None
+        } else {
+            Some(AUDIO_FORMATS_ALL[self.len - 1])
+        }
+    }
 }
 
 impl ExactSizeIterator for AudioFormatIterator {}
 
+impl std::iter::FusedIterator for AudioFormatIterator {}
+
 impl DoubleEndedIterator for AudioFormatIterator {
     fn next_back(&mut self) -> Option<Self::Item> {
         if self.idx >= self.len {
             None
         } else {
-            let fmt = AUDIO_FORMATS_ALL[self.len - 1];
             self.len -= 1;
+            let fmt = AUDIO_FORMATS_ALL[self.len];
+            Some(fmt)
+        }
+    }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.len.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.len;
+            None
+        } else {
+            self.len = end - 1;
+            let fmt = AUDIO_FORMATS_ALL[self.len];
             Some(fmt)
         }
     }
diff --git a/gstreamer-pbutils/src/discoverer_stream_info.rs b/gstreamer-pbutils/src/discoverer_stream_info.rs
index 339d629d4..b3d697b8a 100644
--- a/gstreamer-pbutils/src/discoverer_stream_info.rs
+++ b/gstreamer-pbutils/src/discoverer_stream_info.rs
@@ -44,3 +44,5 @@ impl DiscovererStreamInfo {
         }
     }
 }
+
+impl std::iter::FusedIterator for Iter {}
diff --git a/gstreamer-sdp/src/sdp_media.rs b/gstreamer-sdp/src/sdp_media.rs
index 04a5f4449..61bbf24a4 100644
--- a/gstreamer-sdp/src/sdp_media.rs
+++ b/gstreamer-sdp/src/sdp_media.rs
@@ -656,8 +656,8 @@ macro_rules! define_iter(
     #[derive(Debug)]
     pub struct $name<'a> {
         media: &'a SDPMediaRef,
-        idx: u32,
-        len: u32,
+        idx: usize,
+        len: usize,
     }
 
     impl<'a> $name<'a> {
@@ -668,7 +668,7 @@ macro_rules! define_iter(
             $name {
                 media,
                 idx: 0,
-                len,
+                len: len as usize,
             }
         }
     }
@@ -681,20 +681,40 @@ macro_rules! define_iter(
                 return None;
             }
 
-            let item = $get_item(self.media, self.idx)?;
+            let item = $get_item(self.media, self.idx as u32).unwrap();
             self.idx += 1;
             Some(item)
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {
-            if self.idx == self.len {
-                return (0, Some(0))
-            }
-
-            let remaining = (self.len - self.idx) as usize;
+            let remaining = self.len - self.idx;
 
             (remaining, Some(remaining))
         }
+
+
+        fn count(self) -> usize {
+            self.len - self.idx
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.idx.overflowing_add(n);
+            if end >= self.len || overflow {
+                self.idx = self.len;
+                None
+            } else {
+                self.idx = end + 1;
+                Some($get_item(self.media, end as u32).unwrap())
+            }
+        }
+
+        fn last(self) -> Option<Self::Item> {
+            if self.idx == self.len {
+                None
+            } else {
+                Some($get_item(self.media, self.len as u32 - 1).unwrap())
+            }
+        }
     }
 
     impl<'a> DoubleEndedIterator for $name<'a> {
@@ -705,11 +725,24 @@ macro_rules! define_iter(
 
             self.len -= 1;
 
-            $get_item(self.media, self.len)
+            Some($get_item(self.media, self.len as u32).unwrap())
+        }
+
+        fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.len.overflowing_sub(n);
+            if end <= self.idx || overflow {
+                self.idx = self.len;
+                None
+            } else {
+                self.len = end - 1;
+                Some($get_item(self.media, self.len as u32).unwrap())
+            }
         }
     }
 
     impl<'a> ExactSizeIterator for $name<'a> {}
+
+    impl<'a> std::iter::FusedIterator for $name<'a> {}
     }
 );
 
diff --git a/gstreamer-sdp/src/sdp_message.rs b/gstreamer-sdp/src/sdp_message.rs
index 2eca449b6..aa12d36f0 100644
--- a/gstreamer-sdp/src/sdp_message.rs
+++ b/gstreamer-sdp/src/sdp_message.rs
@@ -1009,8 +1009,8 @@ macro_rules! define_iter(
     #[derive(Debug)]
     pub struct $name<'a> {
         message: &'a SDPMessageRef,
-        idx: u32,
-        len: u32,
+        idx: usize,
+        len: usize,
     }
 
     impl<'a> $name<'a> {
@@ -1021,7 +1021,7 @@ macro_rules! define_iter(
             $name {
                 message,
                 idx: 0,
-                len,
+                len: len as usize,
             }
         }
     }
@@ -1034,20 +1034,39 @@ macro_rules! define_iter(
                 return None;
             }
 
-            let item = $get_item(self.message, self.idx)?;
+            let item = $get_item(self.message, self.idx as u32).unwrap();
             self.idx += 1;
             Some(item)
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {
-            if self.idx == self.len {
-                return (0, Some(0))
-            }
-
-            let remaining = (self.len - self.idx) as usize;
+            let remaining = self.len - self.idx;
 
             (remaining, Some(remaining))
         }
+
+        fn count(self) -> usize {
+            self.len - self.idx
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.idx.overflowing_add(n);
+            if end >= self.len || overflow {
+                self.idx = self.len;
+                None
+            } else {
+                self.idx = end + 1;
+                Some($get_item(self.message, end as u32).unwrap())
+            }
+        }
+
+        fn last(self) -> Option<Self::Item> {
+            if self.idx == self.len {
+                None
+            } else {
+                Some($get_item(self.message, self.len as u32 - 1).unwrap())
+            }
+        }
     }
 
     impl<'a> DoubleEndedIterator for $name<'a> {
@@ -1058,11 +1077,23 @@ macro_rules! define_iter(
 
             self.len -= 1;
 
-            $get_item(self.message, self.len)
+            Some($get_item(self.message, self.len as u32).unwrap())
+        }
+
+        fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.len.overflowing_sub(n);
+            if end <= self.idx || overflow {
+                self.idx = self.len;
+                None
+            } else {
+                self.len = end - 1;
+                Some($get_item(self.message, self.len as u32).unwrap())
+            }
         }
     }
 
     impl<'a> ExactSizeIterator for $name<'a> {}
+    impl<'a> std::iter::FusedIterator for $name<'a> {}
     }
 );
 
@@ -1071,8 +1102,8 @@ macro_rules! define_iter_mut(
     #[derive(Debug)]
     pub struct $name<'a> {
         message: &'a mut SDPMessageRef,
-        idx: u32,
-        len: u32,
+        idx: usize,
+        len: usize,
     }
 
     impl<'a> $name<'a> {
@@ -1083,7 +1114,7 @@ macro_rules! define_iter_mut(
             $name {
                 message,
                 idx: 0,
-                len,
+                len: len as usize,
             }
         }
     }
@@ -1108,20 +1139,43 @@ macro_rules! define_iter_mut(
                 return None;
             }
 
-            let item = $get_item(message, self.idx)?;
+            let item = $get_item(message, self.idx as u32).unwrap();
             self.idx += 1;
             Some(item)
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {
-            if self.idx == self.len {
-                return (0, Some(0))
-            }
-
-            let remaining = (self.len - self.idx) as usize;
+            let remaining = self.len - self.idx;
 
             (remaining, Some(remaining))
         }
+
+
+        fn count(self) -> usize {
+            self.len - self.idx
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            let message = unsafe {
+                &mut *(self.message as *mut SDPMessageRef)
+            };
+            let (end, overflow) = self.idx.overflowing_add(n);
+            if end >= self.len || overflow {
+                self.idx = self.len;
+                None
+            } else {
+                self.idx = end + 1;
+                Some($get_item(message, end as u32).unwrap())
+            }
+        }
+
+        fn last(self) -> Option<Self::Item> {
+            if self.idx == self.len {
+                None
+            } else {
+                Some($get_item(self.message, self.len as u32 - 1).unwrap())
+            }
+        }
     }
 
     impl<'a> DoubleEndedIterator for $name<'a> {
@@ -1134,12 +1188,27 @@ macro_rules! define_iter_mut(
             }
 
             self.len -= 1;
+            Some($get_item(message, self.len as u32).unwrap())
+        }
 
-            $get_item(message, self.len)
+
+        fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+            let message = unsafe {
+                &mut *(self.message as *mut SDPMessageRef)
+            };
+            let (end, overflow) = self.len.overflowing_sub(n);
+            if end <= self.idx || overflow {
+                self.idx = self.len;
+                None
+            } else {
+                self.len = end - 1;
+                Some($get_item(message, self.len as u32).unwrap())
+            }
         }
     }
 
     impl<'a> ExactSizeIterator for $name<'a> {}
+    impl<'a> std::iter::FusedIterator for $name<'a> {}
     }
 );
 
diff --git a/gstreamer-video/src/video_format.rs b/gstreamer-video/src/video_format.rs
index def19095e..d0eb1f158 100644
--- a/gstreamer-video/src/video_format.rs
+++ b/gstreamer-video/src/video_format.rs
@@ -354,10 +354,35 @@ impl Iterator for VideoFormatIterator {
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.len - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.len || overflow {
+            self.idx = self.len;
+            None
+        } else {
+            self.idx = end + 1;
+            Some(VIDEO_FORMATS_ALL[end])
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.len {
+            None
+        } else {
+            Some(VIDEO_FORMATS_ALL[self.len - 1])
+        }
+    }
 }
 
 impl ExactSizeIterator for VideoFormatIterator {}
 
+impl std::iter::FusedIterator for VideoFormatIterator {}
+
 impl DoubleEndedIterator for VideoFormatIterator {
     fn next_back(&mut self) -> Option<Self::Item> {
         if self.idx >= self.len {
@@ -368,6 +393,18 @@ impl DoubleEndedIterator for VideoFormatIterator {
             Some(fmt)
         }
     }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.len.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.len;
+            None
+        } else {
+            self.len = end - 1;
+            let fmt = VIDEO_FORMATS_ALL[self.len];
+            Some(fmt)
+        }
+    }
 }
 pub trait VideoFormatIteratorExt {
     fn into_video_caps(self) -> Option<gst::caps::Builder<gst::caps::NoFeature>>;
diff --git a/gstreamer-video/src/video_meta.rs b/gstreamer-video/src/video_meta.rs
index 1e11a6bcf..a8b136b07 100644
--- a/gstreamer-video/src/video_meta.rs
+++ b/gstreamer-video/src/video_meta.rs
@@ -361,7 +361,7 @@ impl VideoRegionOfInterestMeta {
     pub fn params(&self) -> ParamsIter {
         ParamsIter {
             _meta: self,
-            list: self.0.params,
+            list: ptr::NonNull::new(self.0.params),
         }
     }
 
@@ -395,29 +395,29 @@ impl VideoRegionOfInterestMeta {
 
 pub struct ParamsIter<'a> {
     _meta: &'a VideoRegionOfInterestMeta,
-    list: *const glib::ffi::GList,
+    list: Option<ptr::NonNull<glib::ffi::GList>>,
 }
 
 impl<'a> Iterator for ParamsIter<'a> {
     type Item = &'a gst::StructureRef;
 
     fn next(&mut self) -> Option<&'a gst::StructureRef> {
-        if self.list.is_null() {
-            return None;
-        }
+        match self.list {
+            None => None,
+            Some(list) => unsafe {
+                self.list = ptr::NonNull::new(list.as_ref().next);
+                let data = list.as_ref().data;
 
-        unsafe {
-            let data = (*self.list).data;
-            assert!(!data.is_null());
-            self.list = (*self.list).next;
+                let s = gst::StructureRef::from_glib_borrow(data as *const gst::ffi::GstStructure);
 
-            let s = gst::StructureRef::from_glib_borrow(data as *const gst::ffi::GstStructure);
-
-            Some(s)
+                Some(s)
+            },
         }
     }
 }
 
+impl<'a> std::iter::FusedIterator for ParamsIter<'a> {}
+
 unsafe impl MetaAPI for VideoRegionOfInterestMeta {
     type GstType = ffi::GstVideoRegionOfInterestMeta;
 
diff --git a/gstreamer-video/src/video_overlay_composition.rs b/gstreamer-video/src/video_overlay_composition.rs
index 53be581fb..308a7b4a6 100644
--- a/gstreamer-video/src/video_overlay_composition.rs
+++ b/gstreamer-video/src/video_overlay_composition.rs
@@ -328,7 +328,7 @@ impl VideoOverlayCompositionRef {
         Iter {
             composition: self,
             idx: 0,
-            len: self.n_rectangles(),
+            len: self.n_rectangles() as usize,
         }
     }
 }
@@ -390,33 +390,52 @@ impl<'a> std::iter::FromIterator<&'a VideoOverlayRectangle> for VideoOverlayComp
 
 pub struct Iter<'a> {
     composition: &'a VideoOverlayCompositionRef,
-    idx: u32,
-    len: u32,
+    idx: usize,
+    len: usize,
 }
 
 impl<'a> Iterator for Iter<'a> {
     type Item = VideoOverlayRectangle;
 
     fn next(&mut self) -> Option<Self::Item> {
-        if self.idx == self.len {
+        if self.idx >= self.len {
             return None;
         }
 
-        let rect = self.composition.rectangle(self.idx).unwrap();
+        let rect = self.composition.rectangle(self.idx as u32).unwrap();
         self.idx += 1;
 
         Some(rect)
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.len {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.len - self.idx) as usize;
+        let remaining = self.len - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.len - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.len || overflow {
+            self.idx = self.len;
+            None
+        } else {
+            self.idx = end + 1;
+            Some(self.composition.rectangle(end as u32).unwrap())
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.len {
+            None
+        } else {
+            Some(self.composition.rectangle(self.len as u32 - 1).unwrap())
+        }
+    }
 }
 
 impl<'a> DoubleEndedIterator for Iter<'a> {
@@ -427,10 +446,21 @@ impl<'a> DoubleEndedIterator for Iter<'a> {
 
         self.len -= 1;
 
-        let rect = self.composition.rectangle(self.len).unwrap();
+        Some(self.composition.rectangle(self.len as u32).unwrap())
+    }
 
-        Some(rect)
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.len.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.len;
+            None
+        } else {
+            self.len = end - 1;
+            Some(self.composition.rectangle(self.len as u32).unwrap())
+        }
     }
 }
 
 impl<'a> ExactSizeIterator for Iter<'a> {}
+
+impl<'a> std::iter::FusedIterator for Iter<'a> {}
diff --git a/gstreamer/src/buffer.rs b/gstreamer/src/buffer.rs
index 96de2daa0..4c1746327 100644
--- a/gstreamer/src/buffer.rs
+++ b/gstreamer/src/buffer.rs
@@ -816,6 +816,8 @@ macro_rules! define_meta_iter(
             }
         }
     }
+
+    impl<'a, T: MetaAPI> std::iter::FusedIterator for $name<'a, T> { }
     }
 );
 
@@ -838,8 +840,8 @@ macro_rules! define_iter(
     ($name:ident, $typ:ty, $mtyp:ty, $get_item:expr) => {
     pub struct $name<'a> {
         buffer: $typ,
-        idx: u32,
-        n_memory: u32,
+        idx: usize,
+        n_memory: usize,
     }
 
     impl<'a> fmt::Debug for $name<'a> {
@@ -861,7 +863,7 @@ macro_rules! define_iter(
             $name {
                 buffer,
                 idx: 0,
-                n_memory,
+                n_memory: n_memory as usize,
             }
         }
     }
@@ -876,21 +878,46 @@ macro_rules! define_iter(
 
             #[allow(unused_unsafe)]
             unsafe {
-                let item = $get_item(self.buffer, self.idx)?;
+                let item = $get_item(self.buffer, self.idx as u32).unwrap();
                 self.idx += 1;
                 Some(item)
             }
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {
-            if self.idx == self.n_memory {
-                return (0, Some(0));
-            }
-
-            let remaining = (self.n_memory - self.idx) as usize;
+            let remaining = self.n_memory - self.idx;
 
             (remaining, Some(remaining))
         }
+
+        fn count(self) -> usize {
+            self.n_memory - self.idx
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.idx.overflowing_add(n);
+            if end >= self.n_memory || overflow {
+                self.idx = self.n_memory;
+                None
+            } else {
+                #[allow(unused_unsafe)]
+                unsafe {
+                    self.idx = end + 1;
+                    Some($get_item(self.buffer, end as u32).unwrap())
+                }
+            }
+        }
+
+        fn last(self) -> Option<Self::Item> {
+            if self.idx == self.n_memory {
+                None
+            } else {
+                #[allow(unused_unsafe)]
+                unsafe {
+                    Some($get_item(self.buffer, self.n_memory as u32 - 1).unwrap())
+                }
+            }
+        }
     }
 
     impl<'a> DoubleEndedIterator for $name<'a> {
@@ -899,16 +926,31 @@ macro_rules! define_iter(
                 return None;
             }
 
-            self.n_memory -= 1;
-
             #[allow(unused_unsafe)]
             unsafe {
-                $get_item(self.buffer, self.n_memory)
+                self.n_memory -= 1;
+                Some($get_item(self.buffer, self.n_memory as u32).unwrap())
+            }
+        }
+
+        fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.n_memory.overflowing_sub(n);
+            if end <= self.idx || overflow {
+                self.idx = self.n_memory;
+                None
+            } else {
+                #[allow(unused_unsafe)]
+                unsafe {
+                    self.n_memory = end - 1;
+                    Some($get_item(self.buffer, self.n_memory as u32).unwrap())
+                }
             }
         }
     }
 
     impl<'a> ExactSizeIterator for $name<'a> {}
+
+    impl<'a> std::iter::FusedIterator for $name<'a> {}
     }
 );
 
diff --git a/gstreamer/src/bufferlist.rs b/gstreamer/src/bufferlist.rs
index d3fe8f041..c7938a476 100644
--- a/gstreamer/src/bufferlist.rs
+++ b/gstreamer/src/bufferlist.rs
@@ -215,8 +215,8 @@ macro_rules! define_iter(
     #[derive(Debug)]
     pub struct $name<'a> {
         list: &'a BufferListRef,
-        idx: u32,
-        size: u32,
+        idx: usize,
+        size: usize,
     }
 
     impl<'a> $name<'a> {
@@ -225,7 +225,7 @@ macro_rules! define_iter(
             $name {
                 list,
                 idx: 0,
-                size: list.len() as u32,
+                size: list.len() as usize,
             }
         }
     }
@@ -238,21 +238,40 @@ macro_rules! define_iter(
                 return None;
             }
 
-            let item = $get_item(self.list, self.idx)?;
+            let item = $get_item(self.list, self.idx as u32).unwrap();
             self.idx += 1;
 
             Some(item)
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {
-            if self.idx == self.size {
-                return (0, Some(0));
-            }
-
-            let remaining = (self.size - self.idx) as usize;
+            let remaining = self.size - self.idx;
 
             (remaining, Some(remaining))
         }
+
+        fn count(self) -> usize {
+            self.size - self.idx
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.idx.overflowing_add(n);
+            if end >= self.size || overflow {
+                self.idx = self.size;
+                None
+            } else {
+                self.idx = end + 1;
+                Some($get_item(self.list, end as u32).unwrap())
+            }
+        }
+
+        fn last(self) -> Option<Self::Item> {
+            if self.idx == self.size {
+                None
+            } else {
+                Some($get_item(self.list, self.size as u32 - 1).unwrap())
+            }
+        }
     }
 
     impl<'a> DoubleEndedIterator for $name<'a> {
@@ -262,11 +281,23 @@ macro_rules! define_iter(
             }
 
             self.size -= 1;
-            $get_item(self.list, self.size)
+            Some($get_item(self.list, self.size as u32).unwrap())
+        }
+
+        fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.size.overflowing_sub(n);
+            if end <= self.idx || overflow {
+                self.idx = self.size;
+                None
+            } else {
+                self.size = end - 1;
+                Some($get_item(self.list, self.size as u32).unwrap())
+            }
         }
     }
 
     impl<'a> ExactSizeIterator for $name<'a> {}
+    impl<'a> std::iter::FusedIterator for $name<'a> {}
     }
 );
 
diff --git a/gstreamer/src/caps.rs b/gstreamer/src/caps.rs
index 79f9f6e7d..c732ea3ab 100644
--- a/gstreamer/src/caps.rs
+++ b/gstreamer/src/caps.rs
@@ -597,8 +597,8 @@ macro_rules! define_iter(
     #[derive(Debug)]
     pub struct $name<'a> {
         caps: $typ,
-        idx: u32,
-        n_structures: u32,
+        idx: usize,
+        n_structures: usize,
     }
 
     impl<'a> $name<'a> {
@@ -609,7 +609,7 @@ macro_rules! define_iter(
             $name {
                 caps,
                 idx: 0,
-                n_structures,
+                n_structures: n_structures as usize,
             }
         }
     }
@@ -623,21 +623,44 @@ macro_rules! define_iter(
             }
 
             unsafe {
-                let item = $get_item(self.caps, self.idx)?;
+                let item = $get_item(self.caps, self.idx as u32).unwrap();
                 self.idx += 1;
                 Some(item)
             }
         }
 
         fn size_hint(&self) -> (usize, Option<usize>) {
-            if self.idx == self.n_structures {
-                return (0, Some(0));
-            }
-
-            let remaining = (self.n_structures - self.idx) as usize;
+            let remaining = self.n_structures - self.idx;
 
             (remaining, Some(remaining))
         }
+
+        fn count(self) -> usize {
+            self.n_structures - self.idx
+        }
+
+        fn nth(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.idx.overflowing_add(n);
+            if end >= self.n_structures || overflow {
+                self.idx = self.n_structures;
+                None
+            } else {
+                unsafe {
+                    self.idx = end + 1;
+                    Some($get_item(self.caps, end as u32).unwrap())
+                }
+            }
+        }
+
+        fn last(self) -> Option<Self::Item> {
+            if self.idx == self.n_structures {
+                None
+            } else {
+                unsafe {
+                    Some($get_item(self.caps, self.n_structures as u32 - 1).unwrap())
+                }
+            }
+        }
     }
 
     impl<'a> DoubleEndedIterator for $name<'a> {
@@ -649,12 +672,27 @@ macro_rules! define_iter(
             self.n_structures -= 1;
 
             unsafe {
-                $get_item(self.caps, self.n_structures)
+                Some($get_item(self.caps, self.n_structures as u32).unwrap())
+            }
+        }
+
+        fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+            let (end, overflow) = self.n_structures.overflowing_sub(n);
+            if end <= self.idx || overflow {
+                self.idx = self.n_structures;
+                None
+            } else {
+                self.n_structures = end - 1;
+                unsafe {
+                    Some($get_item(self.caps, self.n_structures as u32).unwrap())
+                }
             }
         }
     }
 
     impl<'a> ExactSizeIterator for $name<'a> {}
+
+    impl<'a> std::iter::FusedIterator for $name<'a> {}
     }
 );
 
diff --git a/gstreamer/src/caps_features.rs b/gstreamer/src/caps_features.rs
index af651a682..56b2114f7 100644
--- a/gstreamer/src/caps_features.rs
+++ b/gstreamer/src/caps_features.rs
@@ -479,8 +479,8 @@ impl glib::value::ToValueOptional for CapsFeaturesRef {
 #[derive(Debug)]
 pub struct Iter<'a> {
     caps_features: &'a CapsFeaturesRef,
-    idx: u32,
-    n_features: u32,
+    idx: usize,
+    n_features: usize,
 }
 
 impl<'a> Iter<'a> {
@@ -491,7 +491,7 @@ impl<'a> Iter<'a> {
         Iter {
             caps_features,
             idx: 0,
-            n_features,
+            n_features: n_features as usize,
         }
     }
 }
@@ -505,10 +505,9 @@ impl<'a> Iterator for Iter<'a> {
         }
 
         unsafe {
-            let feature = ffi::gst_caps_features_get_nth(self.caps_features.as_ptr(), self.idx);
-            if feature.is_null() {
-                return None;
-            }
+            let feature =
+                ffi::gst_caps_features_get_nth(self.caps_features.as_ptr(), self.idx as u32);
+            assert!(!feature.is_null());
 
             self.idx += 1;
 
@@ -517,14 +516,46 @@ impl<'a> Iterator for Iter<'a> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.n_features {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.n_features - self.idx) as usize;
+        let remaining = self.n_features - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.n_features - self.idx
+    }
+
+    // checker-ignore-item
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.n_features || overflow {
+            self.idx = self.n_features;
+            None
+        } else {
+            unsafe {
+                self.idx = end + 1;
+                let feature =
+                    ffi::gst_caps_features_get_nth(self.caps_features.as_ptr(), end as u32);
+                assert!(!feature.is_null());
+                Some(CStr::from_ptr(feature).to_str().unwrap())
+            }
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.n_features {
+            None
+        } else {
+            unsafe {
+                let feature = ffi::gst_caps_features_get_nth(
+                    self.caps_features.as_ptr(),
+                    self.n_features as u32 - 1,
+                );
+                assert!(!feature.is_null());
+                Some(CStr::from_ptr(feature).to_str().unwrap())
+            }
+        }
+    }
 }
 
 impl<'a> DoubleEndedIterator for Iter<'a> {
@@ -537,18 +568,37 @@ impl<'a> DoubleEndedIterator for Iter<'a> {
 
         unsafe {
             let feature =
-                ffi::gst_caps_features_get_nth(self.caps_features.as_ptr(), self.n_features);
-            if feature.is_null() {
-                return None;
-            }
+                ffi::gst_caps_features_get_nth(self.caps_features.as_ptr(), self.n_features as u32);
+            assert!(!feature.is_null());
 
             Some(CStr::from_ptr(feature).to_str().unwrap())
         }
     }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.n_features.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.n_features;
+            None
+        } else {
+            unsafe {
+                self.n_features = end - 1;
+                let feature = ffi::gst_caps_features_get_nth(
+                    self.caps_features.as_ptr(),
+                    self.n_features as u32,
+                );
+                assert!(!feature.is_null());
+
+                Some(CStr::from_ptr(feature).to_str().unwrap())
+            }
+        }
+    }
 }
 
 impl<'a> ExactSizeIterator for Iter<'a> {}
 
+impl<'a> std::iter::FusedIterator for Iter<'a> {}
+
 impl<'a> IntoIterator for &'a CapsFeaturesRef {
     type IntoIter = Iter<'a>;
     type Item = &'a str;
diff --git a/gstreamer/src/iterator.rs b/gstreamer/src/iterator.rs
index f20977072..9a916c69c 100644
--- a/gstreamer/src/iterator.rs
+++ b/gstreamer/src/iterator.rs
@@ -691,6 +691,8 @@ where
     }
 }
 
+impl<T> iter::FusedIterator for StdIterator<T> where for<'a> T: FromValue<'a> + 'static {}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/gstreamer/src/stream_collection.rs b/gstreamer/src/stream_collection.rs
index 7adc2424a..661241f8e 100644
--- a/gstreamer/src/stream_collection.rs
+++ b/gstreamer/src/stream_collection.rs
@@ -13,8 +13,8 @@ use std::mem::transmute;
 #[derive(Debug)]
 pub struct Iter<'a> {
     collection: &'a StreamCollection,
-    idx: u32,
-    size: u32,
+    idx: usize,
+    size: usize,
 }
 
 impl<'a> Iter<'a> {
@@ -23,7 +23,7 @@ impl<'a> Iter<'a> {
         Iter {
             collection,
             idx: 0,
-            size: collection.len() as u32,
+            size: collection.len() as usize,
         }
     }
 }
@@ -36,21 +36,40 @@ impl<'a> Iterator for Iter<'a> {
             return None;
         }
 
-        let item = self.collection.stream(self.idx);
+        let item = self.collection.stream(self.idx as u32).unwrap();
         self.idx += 1;
 
-        item
+        Some(item)
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.size {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.size - self.idx) as usize;
+        let remaining = self.size - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.size - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.size || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.idx = end + 1;
+            Some(self.collection.stream(end as u32).unwrap())
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.size {
+            None
+        } else {
+            Some(self.collection.stream(self.size as u32 - 1).unwrap())
+        }
+    }
 }
 
 impl<'a> DoubleEndedIterator for Iter<'a> {
@@ -60,12 +79,25 @@ impl<'a> DoubleEndedIterator for Iter<'a> {
         }
 
         self.size -= 1;
-        self.collection.stream(self.size)
+        Some(self.collection.stream(self.size as u32).unwrap())
+    }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.size.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.size = end - 1;
+            Some(self.collection.stream(self.size as u32).unwrap())
+        }
     }
 }
 
 impl<'a> ExactSizeIterator for Iter<'a> {}
 
+impl<'a> std::iter::FusedIterator for Iter<'a> {}
+
 #[derive(Debug, Clone)]
 #[must_use = "The builder must be built to be used"]
 pub struct StreamCollectionBuilder(StreamCollection);
diff --git a/gstreamer/src/structure.rs b/gstreamer/src/structure.rs
index 4914ebf24..2dd933e09 100644
--- a/gstreamer/src/structure.rs
+++ b/gstreamer/src/structure.rs
@@ -852,8 +852,8 @@ impl glib::value::ToValueOptional for StructureRef {
 #[derive(Debug)]
 pub struct FieldIterator<'a> {
     structure: &'a StructureRef,
-    idx: u32,
-    n_fields: u32,
+    idx: usize,
+    n_fields: usize,
 }
 
 impl<'a> FieldIterator<'a> {
@@ -864,7 +864,7 @@ impl<'a> FieldIterator<'a> {
         FieldIterator {
             structure,
             idx: 0,
-            n_fields,
+            n_fields: n_fields as usize,
         }
     }
 }
@@ -877,20 +877,14 @@ impl<'a> Iterator for FieldIterator<'a> {
             return None;
         }
 
-        if let Some(field_name) = self.structure.nth_field_name(self.idx) {
-            self.idx += 1;
-            Some(field_name)
-        } else {
-            None
-        }
+        let field_name = self.structure.nth_field_name(self.idx as u32).unwrap();
+        self.idx += 1;
+
+        Some(field_name)
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.n_fields {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.n_fields - self.idx) as usize;
+        let remaining = self.n_fields - self.idx;
 
         (remaining, Some(remaining))
     }
@@ -903,12 +897,14 @@ impl<'a> DoubleEndedIterator for FieldIterator<'a> {
         }
 
         self.n_fields -= 1;
-        self.structure.nth_field_name(self.n_fields)
+        Some(self.structure.nth_field_name(self.n_fields as u32).unwrap())
     }
 }
 
 impl<'a> ExactSizeIterator for FieldIterator<'a> {}
 
+impl<'a> std::iter::FusedIterator for FieldIterator<'a> {}
+
 #[derive(Debug)]
 pub struct Iter<'a> {
     iter: FieldIterator<'a>,
@@ -927,32 +923,51 @@ impl<'a> Iterator for Iter<'a> {
     type Item = (&'static str, &'a SendValue);
 
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some(f) = self.iter.next() {
-            let v = self.iter.structure.value(f);
-            Some((f, v.unwrap()))
-        } else {
-            None
-        }
+        let f = self.iter.next()?;
+        let v = self.iter.structure.value(f);
+        Some((f, v.unwrap()))
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
+
+    fn count(self) -> usize {
+        self.iter.count()
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let f = self.iter.nth(n)?;
+        let v = self.iter.structure.value(f);
+        Some((f, v.unwrap()))
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        let structure = self.iter.structure;
+        let f = self.iter.last()?;
+        let v = structure.value(f);
+        Some((f, v.unwrap()))
+    }
 }
 
 impl<'a> DoubleEndedIterator for Iter<'a> {
     fn next_back(&mut self) -> Option<Self::Item> {
-        if let Some(f) = self.iter.next_back() {
-            let v = self.iter.structure.value(f);
-            Some((f, v.unwrap()))
-        } else {
-            None
-        }
+        let f = self.iter.next_back()?;
+        let v = self.iter.structure.value(f);
+        Some((f, v.unwrap()))
+    }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let f = self.iter.nth_back(n)?;
+        let v = self.iter.structure.value(f);
+        Some((f, v.unwrap()))
     }
 }
 
 impl<'a> ExactSizeIterator for Iter<'a> {}
 
+impl<'a> std::iter::FusedIterator for Iter<'a> {}
+
 impl<'a> IntoIterator for &'a StructureRef {
     type IntoIter = Iter<'a>;
     type Item = (&'static str, &'a SendValue);
diff --git a/gstreamer/src/tags.rs b/gstreamer/src/tags.rs
index 2f200caa7..cc818cd80 100644
--- a/gstreamer/src/tags.rs
+++ b/gstreamer/src/tags.rs
@@ -606,8 +606,8 @@ impl Eq for TagListRef {}
 #[derive(Debug)]
 pub struct TagIter<'a, T: Tag<'a>> {
     taglist: &'a TagListRef,
-    idx: u32,
-    size: u32,
+    idx: usize,
+    size: usize,
     phantom: PhantomData<T>,
 }
 
@@ -617,7 +617,7 @@ impl<'a, T: Tag<'a>> TagIter<'a, T> {
         TagIter {
             taglist,
             idx: 0,
-            size: taglist.size::<T>(),
+            size: taglist.size::<T>() as usize,
             phantom: PhantomData,
         }
     }
@@ -635,21 +635,40 @@ where
             return None;
         }
 
-        let item = self.taglist.index::<T>(self.idx);
+        let item = self.taglist.index::<T>(self.idx as u32);
         self.idx += 1;
 
         item
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.size {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.size - self.idx) as usize;
+        let remaining = self.size - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.size - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.size || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.idx = end + 1;
+            self.taglist.index::<T>(end as u32)
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.size {
+            None
+        } else {
+            self.taglist.index::<T>(self.size as u32 - 1)
+        }
+    }
 }
 
 impl<'a, T: Tag<'a>> DoubleEndedIterator for TagIter<'a, T>
@@ -663,7 +682,18 @@ where
         }
 
         self.size -= 1;
-        self.taglist.index::<T>(self.size)
+        self.taglist.index::<T>(self.size as u32)
+    }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.size.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.size = end - 1;
+            self.taglist.index::<T>(self.size as u32)
+        }
     }
 }
 
@@ -674,12 +704,19 @@ where
 {
 }
 
+impl<'a, T: Tag<'a>> std::iter::FusedIterator for TagIter<'a, T>
+where
+    <T as Tag<'a>>::TagType: 'a,
+    T: 'a,
+{
+}
+
 #[derive(Debug)]
 pub struct GenericTagIter<'a> {
     taglist: &'a TagListRef,
     name: &'a str,
-    idx: u32,
-    size: u32,
+    idx: usize,
+    size: usize,
 }
 
 impl<'a> GenericTagIter<'a> {
@@ -689,7 +726,7 @@ impl<'a> GenericTagIter<'a> {
             taglist,
             name,
             idx: 0,
-            size: taglist.size_by_name(name),
+            size: taglist.size_by_name(name) as usize,
         }
     }
 }
@@ -702,21 +739,40 @@ impl<'a> Iterator for GenericTagIter<'a> {
             return None;
         }
 
-        let item = self.taglist.index_generic(self.name, self.idx);
+        let item = self.taglist.index_generic(self.name, self.idx as u32);
         self.idx += 1;
 
         item
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.size {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.size - self.idx) as usize;
+        let remaining = self.size - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.size - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.size || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.idx = end + 1;
+            self.taglist.index_generic(self.name, end as u32)
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.size {
+            None
+        } else {
+            self.taglist.index_generic(self.name, self.size as u32 - 1)
+        }
+    }
 }
 
 impl<'a> DoubleEndedIterator for GenericTagIter<'a> {
@@ -726,17 +782,30 @@ impl<'a> DoubleEndedIterator for GenericTagIter<'a> {
         }
 
         self.size -= 1;
-        self.taglist.index_generic(self.name, self.size)
+        self.taglist.index_generic(self.name, self.size as u32)
+    }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.size.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.size = end - 1;
+            self.taglist.index_generic(self.name, self.size as u32)
+        }
     }
 }
 
 impl<'a> ExactSizeIterator for GenericTagIter<'a> {}
 
+impl<'a> std::iter::FusedIterator for GenericTagIter<'a> {}
+
 #[derive(Debug)]
 pub struct GenericIter<'a> {
     taglist: &'a TagListRef,
-    idx: u32,
-    size: u32,
+    idx: usize,
+    size: usize,
 }
 
 impl<'a> GenericIter<'a> {
@@ -746,7 +815,7 @@ impl<'a> GenericIter<'a> {
         GenericIter {
             taglist,
             idx: 0,
-            size: if size > 0 { size as u32 } else { 0 },
+            size: if size > 0 { size as usize } else { 0 },
         }
     }
 }
@@ -759,7 +828,7 @@ impl<'a> Iterator for GenericIter<'a> {
             return None;
         }
 
-        let name = self.taglist.nth_tag_name(self.idx);
+        let name = self.taglist.nth_tag_name(self.idx as u32);
         let item = (name, self.taglist.iter_tag_generic(name));
         self.idx += 1;
 
@@ -767,14 +836,35 @@ impl<'a> Iterator for GenericIter<'a> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.size {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.size - self.idx) as usize;
+        let remaining = self.size - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.size - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.size || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.idx = end + 1;
+            let name = self.taglist.nth_tag_name(end as u32);
+            Some((name, self.taglist.iter_tag_generic(name)))
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.size {
+            None
+        } else {
+            let name = self.taglist.nth_tag_name(self.size as u32 - 1);
+            Some((name, self.taglist.iter_tag_generic(name)))
+        }
+    }
 }
 
 impl<'a> DoubleEndedIterator for GenericIter<'a> {
@@ -784,18 +874,32 @@ impl<'a> DoubleEndedIterator for GenericIter<'a> {
         }
 
         self.size -= 1;
-        let name = self.taglist.nth_tag_name(self.idx);
+        let name = self.taglist.nth_tag_name(self.idx as u32);
         Some((name, self.taglist.iter_tag_generic(name)))
     }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.size.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.size = end - 1;
+            let name = self.taglist.nth_tag_name(self.size as u32);
+            Some((name, self.taglist.iter_tag_generic(name)))
+        }
+    }
 }
 
 impl<'a> ExactSizeIterator for GenericIter<'a> {}
 
+impl<'a> std::iter::FusedIterator for GenericIter<'a> {}
+
 #[derive(Debug)]
 pub struct Iter<'a> {
     taglist: &'a TagListRef,
-    idx: u32,
-    size: u32,
+    idx: usize,
+    size: usize,
 }
 
 impl<'a> Iter<'a> {
@@ -805,7 +909,7 @@ impl<'a> Iter<'a> {
         Iter {
             taglist,
             idx: 0,
-            size: if size > 0 { size as u32 } else { 0 },
+            size: if size > 0 { size as usize } else { 0 },
         }
     }
 }
@@ -818,7 +922,7 @@ impl<'a> Iterator for Iter<'a> {
             return None;
         }
 
-        let name = self.taglist.nth_tag_name(self.idx);
+        let name = self.taglist.nth_tag_name(self.idx as u32);
         let item = (name, self.taglist.generic(name).unwrap());
         self.idx += 1;
 
@@ -826,14 +930,35 @@ impl<'a> Iterator for Iter<'a> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        if self.idx == self.size {
-            return (0, Some(0));
-        }
-
-        let remaining = (self.size - self.idx) as usize;
+        let remaining = self.size - self.idx;
 
         (remaining, Some(remaining))
     }
+
+    fn count(self) -> usize {
+        self.size - self.idx
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.idx.overflowing_add(n);
+        if end >= self.size || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.idx = end + 1;
+            let name = self.taglist.nth_tag_name(end as u32);
+            Some((name, self.taglist.generic(name).unwrap()))
+        }
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        if self.idx == self.size {
+            None
+        } else {
+            let name = self.taglist.nth_tag_name(self.size as u32 - 1);
+            Some((name, self.taglist.generic(name).unwrap()))
+        }
+    }
 }
 
 impl<'a> DoubleEndedIterator for Iter<'a> {
@@ -843,13 +968,27 @@ impl<'a> DoubleEndedIterator for Iter<'a> {
         }
 
         self.size -= 1;
-        let name = self.taglist.nth_tag_name(self.idx);
+        let name = self.taglist.nth_tag_name(self.idx as u32);
         Some((name, self.taglist.generic(name).unwrap()))
     }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.size.overflowing_sub(n);
+        if end <= self.idx || overflow {
+            self.idx = self.size;
+            None
+        } else {
+            self.size = end - 1;
+            let name = self.taglist.nth_tag_name(self.size as u32);
+            Some((name, self.taglist.generic(name).unwrap()))
+        }
+    }
 }
 
 impl<'a> ExactSizeIterator for Iter<'a> {}
 
+impl<'a> std::iter::FusedIterator for Iter<'a> {}
+
 #[doc(alias = "gst_tag_exists")]
 pub fn tag_exists(name: &str) -> bool {
     skip_assert_initialized!();