textwrap: expose accumulate-time property

In its standard mode, textwrap simply splits up text in chained
buffers into multiple lines / buffers, not keeping any state.

When accumulate-time is specified, multiple input buffers will be
wrapped together, outputting one-line buffers of text once a
sufficient width (specified by the columns property) is reached,
or the interval between two input buffers is greater than
accumulate-time.

This is useful to format the output of an element such as
awstranscribe, which outputs its transcription with one buffer
per word.

text/wrap/src/gsttextwrap/imp.rs

@@ -20,11 +20,12 @@ use glib::subclass;
 use glib::subclass::prelude::*;
 use gst::prelude::*;
 use gst::subclass::prelude::*;
-use gst::{gst_error, gst_info};
+use gst::{gst_error, gst_info, gst_log};
 
 use std::default::Default;
 use std::fs::File;
 use std::io;
+use std::mem;
 use std::sync::Mutex;
 
 use once_cell::sync::Lazy;
@@ -42,8 +43,9 @@ static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
 const DEFAULT_DICTIONARY: Option<String> = None;
 const DEFAULT_COLUMNS: u32 = 32; /* CEA 608 max columns */
 const DEFAULT_LINES: u32 = 0;
+const DEFAULT_ACCUMULATE: i64 = -1;
 
-static PROPERTIES: [subclass::Property; 3] = [
+static PROPERTIES: [subclass::Property; 4] = [
     subclass::Property("dictionary", |name| {
         glib::ParamSpec::string(
             name,
@@ -76,6 +78,17 @@ static PROPERTIES: [subclass::Property; 3] = [
             glib::ParamFlags::READWRITE,
         )
     }),
+    subclass::Property("accumulate-time", |name| {
+        glib::ParamSpec::int64(
+            name,
+            "accumulate-time",
+            "Cut-off time for input text accumulation (-1=do not accumulate)",
+            -1,
+            std::i64::MAX,
+            DEFAULT_ACCUMULATE,
+            glib::ParamFlags::READWRITE,
+        )
+    }),
 ];
 
 #[derive(Debug, Clone)]
@@ -83,6 +96,7 @@ struct Settings {
     dictionary: Option<String>,
     columns: u32,
     lines: u32,
+    accumulate_time: gst::ClockTime,
 }
 
 impl Default for Settings {
@@ -91,17 +105,28 @@ impl Default for Settings {
             dictionary: DEFAULT_DICTIONARY,
             columns: DEFAULT_COLUMNS, /* CEA 608 max columns */
             lines: DEFAULT_LINES,
+            accumulate_time: gst::CLOCK_TIME_NONE,
         }
     }
 }
 
 struct State {
     options: Option<textwrap::Options<'static, Box<dyn textwrap::WordSplitter + Send>>>,
+
+    current_text: String,
+    start_ts: gst::ClockTime,
+    end_ts: gst::ClockTime,
 }
 
 impl Default for State {
     fn default() -> Self {
-        Self { options: None }
+        Self {
+            options: None,
+
+            current_text: "".to_string(),
+            start_ts: gst::CLOCK_TIME_NONE,
+            end_ts: gst::CLOCK_TIME_NONE,
+        }
     }
 }
 
@@ -192,30 +217,128 @@ impl TextWrap {
             gst::FlowError::Error
         })?;
 
-        let lines = self.settings.lock().unwrap().lines;
+        let accumulate_time = self.settings.lock().unwrap().accumulate_time;
+        let mut state = self.state.lock().unwrap();
 
-        let data = {
-            let state = self.state.lock().unwrap();
-            let options = state
-                .options
-                .as_ref()
-                .expect("We should have a wrapper by now");
-            textwrap::fill(data, options)
-        };
-
-        // If the lines property was set, we want to split the result into buffers
-        // of at most N lines. We compute the duration for each of those based on
-        // the total number of words, and the number of words in each of the split-up
-        // buffers.
-        if lines > 0 {
+        if accumulate_time.is_some() {
             let mut bufferlist = gst::BufferList::new();
+
+            if state.end_ts.is_some() && state.end_ts + accumulate_time < buffer.get_pts() {
+                let mut buf = gst::Buffer::from_mut_slice(
+                    mem::replace(&mut state.current_text, String::new()).into_bytes(),
+                );
+                {
+                    let buf_mut = buf.get_mut().unwrap();
+                    buf_mut.set_pts(state.start_ts);
+                    buf_mut.set_duration(state.end_ts - state.start_ts);
+                }
+                bufferlist.get_mut().unwrap().add(buf);
+
+                state.start_ts = gst::CLOCK_TIME_NONE;
+                state.end_ts = gst::CLOCK_TIME_NONE;
+            }
+
             let duration_per_word: gst::ClockTime =
                 duration / data.split_whitespace().count() as u64;
 
-            for chunk in data.lines().collect::<Vec<&str>>().chunks(lines as usize) {
-                let data = chunk.join("\n");
-                let duration: gst::ClockTime =
-                    duration_per_word * data.split_whitespace().count() as u64;
+            if state.start_ts.is_none() {
+                state.start_ts = buffer.get_pts();
+            }
+
+            state.end_ts = buffer.get_pts();
+
+            let words = data.split_whitespace();
+            let mut current_text = state.current_text.to_string();
+
+            for word in words {
+                if !current_text.is_empty() {
+                    current_text.push(' ');
+                }
+                current_text.push_str(word);
+
+                let options = state
+                    .options
+                    .as_ref()
+                    .expect("We should have a wrapper by now");
+
+                let lines = textwrap::wrap(&current_text, options);
+                let len = lines.len();
+                let mut trailing = "".to_string();
+
+                for (i, line) in lines.iter().enumerate() {
+                    if i + 1 == len {
+                        trailing = line.to_string();
+                    } else {
+                        let mut buf = gst::Buffer::from_mut_slice(line.to_string().into_bytes());
+                        {
+                            let buf_mut = buf.get_mut().unwrap();
+                            buf_mut.set_pts(state.start_ts);
+                            buf_mut.set_duration(state.end_ts - state.start_ts);
+                        }
+                        bufferlist.get_mut().unwrap().add(buf);
+                        state.start_ts = state.end_ts;
+                    }
+                }
+
+                current_text = trailing;
+                state.end_ts += duration_per_word;
+            }
+
+            state.current_text = current_text;
+
+            if state.current_text.is_empty() {
+                state.start_ts = gst::CLOCK_TIME_NONE;
+                state.end_ts = gst::CLOCK_TIME_NONE;
+            }
+
+            drop(state);
+
+            if bufferlist.is_empty() {
+                Ok(gst::FlowSuccess::Ok)
+            } else {
+                self.srcpad.push_list(bufferlist)
+            }
+        } else {
+            let lines = self.settings.lock().unwrap().lines;
+
+            let data = {
+                let options = state
+                    .options
+                    .as_ref()
+                    .expect("We should have a wrapper by now");
+                textwrap::fill(data, options)
+            };
+
+            // If the lines property was set, we want to split the result into buffers
+            // of at most N lines. We compute the duration for each of those based on
+            // the total number of words, and the number of words in each of the split-up
+            // buffers.
+            if lines > 0 {
+                let mut bufferlist = gst::BufferList::new();
+                let duration_per_word: gst::ClockTime =
+                    duration / data.split_whitespace().count() as u64;
+
+                for chunk in data.lines().collect::<Vec<&str>>().chunks(lines as usize) {
+                    let data = chunk.join("\n");
+                    let duration: gst::ClockTime =
+                        duration_per_word * data.split_whitespace().count() as u64;
+                    let mut buf = gst::Buffer::from_mut_slice(data.into_bytes());
+
+                    {
+                        let buf = buf.get_mut().unwrap();
+
+                        buf.set_pts(pts);
+                        buf.set_duration(duration);
+                        pts += duration;
+                    }
+
+                    bufferlist.get_mut().unwrap().add(buf);
+                }
+
+                drop(state);
+
+                self.srcpad.push_list(bufferlist)
+            } else {
                 let mut buf = gst::Buffer::from_mut_slice(data.into_bytes());
 
                 {
@@ -223,24 +346,61 @@ impl TextWrap {
 
                     buf.set_pts(pts);
                     buf.set_duration(duration);
-                    pts += duration;
                 }
 
-                bufferlist.get_mut().unwrap().add(buf);
+                drop(state);
+
+                self.srcpad.push(buf)
             }
+        }
+    }
 
-            self.srcpad.push_list(bufferlist)
-        } else {
-            let mut buf = gst::Buffer::from_mut_slice(data.into_bytes());
+    fn sink_event(&self, pad: &gst::Pad, element: &super::TextWrap, event: gst::Event) -> bool {
+        gst_log!(CAT, obj: pad, "Handling event {:?}", event);
 
-            {
-                let buf = buf.get_mut().unwrap();
+        use gst::EventView;
 
-                buf.set_pts(pts);
-                buf.set_duration(duration);
+        match event.view() {
+            EventView::Gap(_) => {
+                let state = self.state.lock().unwrap();
+                /* We are currently accumulating text, no need to forward the gap */
+                if state.start_ts.is_some() {
+                    true
+                } else {
+                    pad.event_default(Some(element), event)
+                }
             }
+            EventView::FlushStart(_) => {
+                let mut state = self.state.lock().unwrap();
+                let options = state.options.take();
+                *state = State::default();
+                state.options = options;
+                drop(state);
+                pad.event_default(Some(element), event)
+            }
+            EventView::Eos(_) => {
+                let mut state = self.state.lock().unwrap();
+                if !state.current_text.is_empty() {
+                    let mut buf = gst::Buffer::from_mut_slice(
+                        mem::replace(&mut state.current_text, String::new()).into_bytes(),
+                    );
+                    {
+                        let buf_mut = buf.get_mut().unwrap();
+                        buf_mut.set_pts(state.start_ts);
+                        buf_mut.set_duration(state.end_ts - state.start_ts);
+                    }
 
-            self.srcpad.push(buf)
+                    state.start_ts = gst::CLOCK_TIME_NONE;
+                    state.end_ts = gst::CLOCK_TIME_NONE;
+
+                    drop(state);
+                    let _ = self.srcpad.push(buf);
+                } else {
+                    drop(state);
+                }
+                pad.event_default(Some(element), event)
+            }
+            _ => pad.event_default(Some(element), event),
         }
     }
 }
@@ -264,6 +424,13 @@ impl ObjectSubclass for TextWrap {
                     |textwrap, element| textwrap.sink_chain(pad, element, buffer),
                 )
             })
+            .event_function(|pad, parent, event| {
+                TextWrap::catch_panic_pad_function(
+                    parent,
+                    || false,
+                    |textwrap, element| textwrap.sink_event(pad, element, event),
+                )
+            })
             .flags(gst::PadFlags::PROXY_CAPS | gst::PadFlags::FIXED_CAPS)
             .build();
 
@@ -344,6 +511,13 @@ impl ObjectImpl for TextWrap {
                 let mut settings = self.settings.lock().unwrap();
                 settings.lines = value.get_some().expect("type checked upstream");
             }
+            subclass::Property("accumulate-time", ..) => {
+                let mut settings = self.settings.lock().unwrap();
+                settings.accumulate_time = match value.get_some().expect("type checked upstream") {
+                    -1i64 => gst::CLOCK_TIME_NONE,
+                    time => (time as u64).into(),
+                };
+            }
             _ => unimplemented!(),
         }
     }
@@ -364,6 +538,13 @@ impl ObjectImpl for TextWrap {
                 let settings = self.settings.lock().unwrap();
                 settings.lines.to_value()
             }
+            subclass::Property("accumulate-time", ..) => {
+                let settings = self.settings.lock().unwrap();
+                match settings.accumulate_time.0 {
+                    Some(time) => (time as i64).to_value(),
+                    None => (-1i64).to_value(),
+                }
+            }
             _ => unimplemented!(),
         }
     }
@@ -377,12 +558,9 @@ impl ElementImpl for TextWrap {
     ) -> Result<gst::StateChangeSuccess, gst::StateChangeError> {
         gst_info!(CAT, obj: element, "Changing state {:?}", transition);
 
-        match transition {
-            gst::StateChange::PausedToReady => {
-                let mut state = self.state.lock().unwrap();
-                *state = State::default();
-            }
-            _ => (),
+        if let gst::StateChange::PausedToReady = transition {
+            let mut state = self.state.lock().unwrap();
+            *state = State::default();
         }
 
         let success = self.parent_change_state(element, transition)?;