sccparse: Add support for seeking

Only pull mode can support seeking for now and reverse playback
is not implemented yet. Note that this restriction is the same as that of
mccparse.

3 files changed, 743 insertions, 56 deletions

diff --git a/video/closedcaption/src/scc_parse/imp.rs b/video/closedcaption/src/scc_parse/imp.rs
index 8fc00054d..ebe3c08f8 100644
--- a/video/closedcaption/src/scc_parse/imp.rs
+++ b/video/closedcaption/src/scc_parse/imp.rs
@@ -20,8 +20,13 @@ use glib::subclass;
 use glib::subclass::prelude::*;
 use gst::prelude::*;
 use gst::subclass::prelude::*;
-use gst::{gst_debug, gst_element_error, gst_error, gst_fixme, gst_log, gst_trace, gst_warning};
+use gst::{
+    gst_debug, gst_element_error, gst_error, gst_fixme, gst_info, gst_log, gst_loggable_error,
+    gst_trace, gst_warning,
+};
 
+use std::cmp;
+use std::convert::TryInto;
 use std::sync::{Mutex, MutexGuard};
 
 use once_cell::sync::Lazy;
@@ -39,6 +44,28 @@ static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
 });
 
 #[derive(Debug)]
+struct PullState {
+    need_stream_start: bool,
+    stream_id: String,
+    offset: u64,
+    duration: gst::ClockTime,
+}
+
+impl PullState {
+    fn new(element: &super::SccParse, pad: &gst::Pad) -> Self {
+        Self {
+            need_stream_start: true,
+            stream_id: pad
+                .create_stream_id(element, Some("src"))
+                .unwrap()
+                .to_string(),
+            offset: 0,
+            duration: gst::CLOCK_TIME_NONE,
+        }
+    }
+}
+
+#[derive(Debug)]
 struct State {
     reader: LineReader<gst::MappedBuffer<gst::buffer::Readable>>,
     parser: SccParser,
@@ -47,6 +74,16 @@ struct State {
     framerate: Option<gst::Fraction>,
     last_position: gst::ClockTime,
     last_timecode: Option<gst_video::ValidVideoTimeCode>,
+    segment: gst::FormattedSegment<gst::ClockTime>,
+
+    // Pull mode
+    pull: Option<PullState>,
+
+    // seeking
+    seeking: bool,
+    discont: bool,
+    seek_seqnum: Option<gst::Seqnum>,
+    need_flush_stop: bool,
 }
 
 impl Default for State {
@@ -59,10 +96,43 @@ impl Default for State {
             framerate: None,
             last_position: gst::CLOCK_TIME_NONE,
             last_timecode: None,
+            segment: gst::FormattedSegment::<gst::ClockTime>::new(),
+            pull: None,
+            seeking: false,
+            discont: false,
+            seek_seqnum: None,
+            need_flush_stop: false,
         }
     }
 }
 
+fn parse_timecode(
+    framerate: gst::Fraction,
+    tc: &TimeCode,
+) -> Result<gst_video::ValidVideoTimeCode, gst::FlowError> {
+    use std::convert::TryFrom;
+
+    let timecode = gst_video::VideoTimeCode::new(
+        framerate,
+        None,
+        if tc.drop_frame {
+            gst_video::VideoTimeCodeFlags::DROP_FRAME
+        } else {
+            gst_video::VideoTimeCodeFlags::empty()
+        },
+        tc.hours,
+        tc.minutes,
+        tc.seconds,
+        tc.frames,
+        0,
+    );
+
+    match gst_video::ValidVideoTimeCode::try_from(timecode).map_err(|_| gst::FlowError::Error) {
+        Ok(timecode) => Ok(timecode),
+        Err(timecode) => Err(timecode),
+    }
+}
+
 impl State {
     #[allow(clippy::type_complexity)]
     fn get_line(
@@ -84,28 +154,11 @@ impl State {
 
     fn handle_timecode(
         &mut self,
-        tc: TimeCode,
+        tc: &TimeCode,
         framerate: gst::Fraction,
         element: &super::SccParse,
     ) -> Result<gst_video::ValidVideoTimeCode, gst::FlowError> {
-        use std::convert::TryFrom;
-
-        let timecode = gst_video::VideoTimeCode::new(
-            framerate,
-            None,
-            if tc.drop_frame {
-                gst_video::VideoTimeCodeFlags::DROP_FRAME
-            } else {
-                gst_video::VideoTimeCodeFlags::empty()
-            },
-            tc.hours,
-            tc.minutes,
-            tc.seconds,
-            tc.frames,
-            0,
-        );
-
-        match gst_video::ValidVideoTimeCode::try_from(timecode) {
+        match parse_timecode(framerate, &tc) {
             Ok(timecode) => Ok(timecode),
             Err(timecode) => {
                 let last_timecode =
@@ -176,6 +229,61 @@ impl State {
                 .unwrap_or(gst::CLOCK_TIME_NONE),
         );
     }
+
+    fn create_events(
+        &mut self,
+        element: &super::SccParse,
+        framerate: Option<gst::Fraction>,
+    ) -> Vec<gst::Event> {
+        let mut events = Vec::new();
+
+        if self.need_flush_stop {
+            let mut b = gst::event::FlushStop::builder(true);
+
+            if let Some(seek_seqnum) = self.seek_seqnum {
+                b = b.seqnum(seek_seqnum);
+            }
+
+            events.push(b.build());
+            self.need_flush_stop = false;
+        }
+
+        if let Some(pull) = &mut self.pull {
+            if pull.need_stream_start {
+                events.push(gst::event::StreamStart::new(&pull.stream_id));
+                pull.need_stream_start = false;
+            }
+        }
+
+        if let Some(framerate) = framerate {
+            if self.framerate != Some(framerate) {
+                self.framerate = Some(framerate);
+
+                let caps = gst::Caps::builder("closedcaption/x-cea-608")
+                    .field("format", &"raw")
+                    .field("framerate", &framerate)
+                    .build();
+                self.framerate = Some(framerate);
+
+                events.push(gst::event::Caps::new(&caps));
+                gst_info!(CAT, obj: element, "Caps changed to {:?}", &caps);
+            }
+        }
+
+        if self.need_segment {
+            let mut b = gst::event::Segment::builder(&self.segment);
+
+            if let Some(seek_seqnum) = self.seek_seqnum {
+                b = b.seqnum(seek_seqnum);
+            }
+
+            events.push(b.build());
+            self.need_segment = false;
+        }
+
+        events.extend(self.pending_events.drain(..));
+        events
+    }
 }
 
 pub struct SccParse {
@@ -228,7 +336,12 @@ impl SccParse {
 
                     break Err(gst::FlowError::Error);
                 }
-                Ok(None) => break Ok(gst::FlowSuccess::Ok),
+                Ok(None) => {
+                    if drain && state.pull.is_some() {
+                        break Err(gst::FlowError::Eos);
+                    }
+                    break Ok(gst::FlowSuccess::Ok);
+                }
             }
         }
     }
@@ -256,27 +369,52 @@ impl SccParse {
             gst::Fraction::new(30, 1)
         };
 
-        let mut events = Vec::new();
+        let mut timecode = state.handle_timecode(&tc, framerate, element)?;
+        let start_time = gst::ClockTime::from(timecode.nsec_since_daily_jam());
+        let segment_start = state.segment.get_start();
+        let clip_buffers = if state.seeking {
+            // If we are in the middle of seeking, check whether this line
+            // contains start frame, and if so, unset seeking flag
+            let num_bufs = (data.len() / 2) as i64;
+            let mut end_timecode = parse_timecode(framerate, &tc).unwrap();
+            // add one more frame here so that add duration of the last frame
+            end_timecode.add_frames(num_bufs + 1);
+            let stop_time = gst::ClockTime::from(end_timecode.nsec_since_daily_jam());
+
+            gst_trace!(
+                CAT,
+                obj: element,
+                "Checking inside of segment, line start {} line stop {} segment start {} num bufs {}",
+                start_time,
+                stop_time,
+                segment_start,
+                num_bufs,
+            );
 
-        if Some(framerate) != state.framerate {
-            let caps = gst::Caps::builder("closedcaption/x-cea-608")
-                .field("format", &"raw")
-                .field("framerate", &framerate)
-                .build();
-            events.push(gst::event::Caps::new(&caps));
-            state.framerate = Some(framerate);
-        }
+            if stop_time > segment_start {
+                state.seeking = false;
+                state.discont = true;
+                state.need_flush_stop = true;
+            }
 
-        if state.need_segment {
-            let segment = gst::FormattedSegment::<gst::format::Time>::new();
-            events.push(gst::event::Segment::new(&segment));
-            state.need_segment = false;
-        }
+            // Still need to scan lines to find the first buffer
+            if state.seeking {
+                drop(state);
+                return Ok(self.state.lock().unwrap());
+            }
 
-        events.extend(state.pending_events.drain(..));
+            true
+        } else {
+            false
+        };
 
-        let mut timecode = state.handle_timecode(tc, framerate, element)?;
-        let mut buffers = gst::BufferList::new_sized(data.len() / 2);
+        let mut buffers = if clip_buffers {
+            gst::BufferList::new()
+        } else {
+            gst::BufferList::new_sized(data.len() / 2)
+        };
+
+        let mut send_eos = false;
         for d in data.chunks_exact(2) {
             let mut buffer = gst::Buffer::with_size(d.len()).unwrap();
             {
@@ -286,13 +424,38 @@ impl SccParse {
 
             state.add_buffer_metadata(&mut buffer, &timecode, framerate, element);
             timecode.increment_frame();
+
+            if clip_buffers {
+                let end_time = buffer.get_pts() + buffer.get_duration();
+                if end_time < segment_start {
+                    gst_trace!(
+                        CAT,
+                        obj: element,
+                        "Skip segment clipped buffer {:?}",
+                        buffer,
+                    );
+
+                    continue;
+                }
+            }
+
+            send_eos = state.segment.get_stop().is_some()
+                && buffer.get_pts() + buffer.get_duration() >= state.segment.get_stop();
+
             let buffers = buffers.get_mut().unwrap();
             buffers.add(buffer);
+
+            // Terminate loop once we found EOS boundary buffer
+            if send_eos {
+                break;
+            }
         }
 
         // Update the last_timecode to the current one
         state.last_timecode = Some(timecode);
 
+        let events = state.create_events(element, Some(framerate));
+
         // Drop our state mutex while we push out buffers or events
         drop(state);
 
@@ -306,9 +469,295 @@ impl SccParse {
             err
         })?;
 
+        if send_eos {
+            return Err(gst::FlowError::Eos);
+        }
+
         Ok(self.state.lock().unwrap())
     }
 
+    fn sink_activate(
+        &self,
+        pad: &gst::Pad,
+        element: &super::SccParse,
+    ) -> Result<(), gst::LoggableError> {
+        let mode = {
+            let mut query = gst::query::Scheduling::new();
+            let mut state = self.state.lock().unwrap();
+
+            state.pull = None;
+
+            if !pad.peer_query(&mut query) {
+                gst_debug!(CAT, obj: pad, "Scheduling query failed on peer");
+                gst::PadMode::Push
+            } else if query
+                .has_scheduling_mode_with_flags(gst::PadMode::Pull, gst::SchedulingFlags::SEEKABLE)
+            {
+                gst_debug!(CAT, obj: pad, "Activating in Pull mode");
+
+                state.pull = Some(PullState::new(element, &self.srcpad));
+
+                gst::PadMode::Pull
+            } else {
+                gst_debug!(CAT, obj: pad, "Activating in Push mode");
+                gst::PadMode::Push
+            }
+        };
+
+        pad.activate_mode(mode, true)?;
+        Ok(())
+    }
+
+    fn start_task(&self, element: &super::SccParse) -> Result<(), gst::LoggableError> {
+        let element_weak = element.downgrade();
+        let pad_weak = self.sinkpad.downgrade();
+        let res = self.sinkpad.start_task(move || {
+            let element = match element_weak.upgrade() {
+                Some(element) => element,
+                None => {
+                    if let Some(pad) = pad_weak.upgrade() {
+                        pad.pause_task().unwrap();
+                    }
+                    return;
+                }
+            };
+
+            let parse = Self::from_instance(&element);
+            parse.loop_fn(&element);
+        });
+        if res.is_err() {
+            return Err(gst_loggable_error!(CAT, "Failed to start pad task"));
+        }
+        Ok(())
+    }
+
+    fn sink_activatemode(
+        &self,
+        _pad: &gst::Pad,
+        element: &super::SccParse,
+        mode: gst::PadMode,
+        active: bool,
+    ) -> Result<(), gst::LoggableError> {
+        if mode == gst::PadMode::Pull {
+            if active {
+                self.start_task(element)?;
+            } else {
+                let _ = self.sinkpad.stop_task();
+            }
+        }
+
+        Ok(())
+    }
+
+    fn scan_duration(
+        &self,
+        element: &super::SccParse,
+    ) -> Result<Option<gst_video::ValidVideoTimeCode>, gst::LoggableError> {
+        gst_debug!(CAT, obj: element, "Scanning duration");
+
+        /* First let's query the bytes duration upstream */
+        let mut q = gst::query::Duration::new(gst::Format::Bytes);
+
+        if !self.sinkpad.peer_query(&mut q) {
+            return Err(gst_loggable_error!(
+                CAT,
+                "Failed to query upstream duration"
+            ));
+        }
+
+        let size = match q.get_result().try_into().unwrap() {
+            gst::format::Bytes(Some(size)) => size,
+            gst::format::Bytes(None) => {
+                return Err(gst_loggable_error!(
+                    CAT,
+                    "Failed to query upstream duration"
+                ));
+            }
+        };
+
+        let mut offset = size;
+        let mut buffers = Vec::new();
+        let mut last_tc = None;
+
+        loop {
+            let scan_size = cmp::min(offset, 4096);
+
+            offset -= scan_size;
+
+            match self.sinkpad.pull_range(offset, scan_size as u32) {
+                Ok(buffer) => {
+                    buffers.push(buffer);
+                }
+                Err(flow) => {
+                    return Err(gst_loggable_error!(
+                        CAT,
+                        "Failed to pull buffer while scanning duration: {:?}",
+                        flow
+                    ));
+                }
+            }
+
+            let mut reader = LineReader::new();
+            let mut parser = SccParser::new_scan_captions();
+
+            for buf in buffers.iter().rev() {
+                let buf = buf
+                    .clone()
+                    .into_mapped_buffer_readable()
+                    .map_err(|_| gst_loggable_error!(CAT, "Failed to map buffer readable"))?;
+
+                reader.push(buf);
+            }
+
+            while let Some(line) = reader.get_line_with_drain(true) {
+                if let Ok(SccLine::Caption(tc, data)) =
+                    parser.parse_line(line).map_err(|err| (line, err))
+                {
+                    let framerate = if tc.drop_frame {
+                        gst::Fraction::new(30000, 1001)
+                    } else {
+                        gst::Fraction::new(30, 1)
+                    };
+
+                    if let Ok(mut timecode) = parse_timecode(framerate, &tc) {
+                        /* We're looking for the total duration */
+                        timecode.add_frames((data.len() / 2) as i64 + 1);
+                        last_tc = Some(timecode);
+                    }
+                }
+            }
+
+            if last_tc.is_some() || offset == 0 {
+                gst_debug!(
+                    CAT,
+                    obj: element,
+                    "Duration scan done, last_tc: {:?}",
+                    last_tc
+                );
+                break (Ok(last_tc));
+            }
+        }
+    }
+
+    fn push_eos(&self, element: &super::SccParse) {
+        let mut state = self.state.lock().unwrap();
+
+        if state.seeking {
+            state.need_flush_stop = true;
+        }
+
+        let mut events = state.create_events(element, None);
+        let mut eos_event = gst::event::Eos::builder();
+
+        if let Some(seek_seqnum) = state.seek_seqnum {
+            eos_event = eos_event.seqnum(seek_seqnum);
+        }
+
+        events.push(eos_event.build());
+
+        // Drop our state mutex while we push out events
+        drop(state);
+
+        for event in events {
+            gst_debug!(CAT, obj: element, "Pushing event {:?}", event);
+            self.srcpad.push_event(event);
+        }
+    }
+
+    fn loop_fn(&self, element: &super::SccParse) {
+        let mut state = self.state.lock().unwrap();
+        let State {
+            ref framerate,
+            ref mut pull,
+            ..
+        } = *state;
+        let mut pull = pull.as_mut().unwrap();
+        let scan_duration = framerate.is_none() && pull.duration.is_none();
+        let offset = pull.offset;
+
+        pull.offset += 4096;
+
+        drop(state);
+
+        let buffer = match self.sinkpad.pull_range(offset, 4096) {
+            Ok(buffer) => Some(buffer),
+            Err(gst::FlowError::Eos) => None,
+            Err(gst::FlowError::Flushing) => {
+                gst_debug!(CAT, obj: &self.sinkpad, "Pausing after pulling buffer, reason: flushing");
+
+                self.sinkpad.pause_task().unwrap();
+                return;
+            }
+            Err(flow) => {
+                gst_error!(CAT, obj: &self.sinkpad, "Failed to pull, reason: {:?}", flow);
+
+                gst_element_error!(
+                    element,
+                    gst::StreamError::Failed,
+                    ["Streaming stopped, failed to pull buffer"]
+                );
+
+                self.sinkpad.pause_task().unwrap();
+                return;
+            }
+        };
+
+        match self.handle_buffer(element, buffer) {
+            Ok(_) => {
+                if scan_duration {
+                    match self.scan_duration(element) {
+                        Ok(Some(tc)) => {
+                            let mut state = self.state.lock().unwrap();
+                            let mut pull = state.pull.as_mut().unwrap();
+                            pull.duration = tc.nsec_since_daily_jam().into();
+                        }
+                        Ok(None) => {
+                            let mut state = self.state.lock().unwrap();
+                            let mut pull = state.pull.as_mut().unwrap();
+                            pull.duration = 0.into();
+                        }
+                        Err(err) => {
+                            err.log();
+
+                            gst_element_error!(
+                                element,
+                                gst::StreamError::Decode,
+                                ["Failed to scan duration"]
+                            );
+
+                            self.sinkpad.pause_task().unwrap();
+                        }
+                    }
+                }
+            }
+            Err(flow) => {
+                match flow {
+                    gst::FlowError::Flushing => {
+                        gst_debug!(CAT, obj: element, "Pausing after flow {:?}", flow);
+                    }
+                    gst::FlowError::Eos => {
+                        self.push_eos(element);
+
+                        gst_debug!(CAT, obj: element, "Pausing after flow {:?}", flow);
+                    }
+                    _ => {
+                        self.push_eos(element);
+
+                        gst_error!(CAT, obj: element, "Pausing after flow {:?}", flow);
+
+                        gst_element_error!(
+                            element,
+                            gst::StreamError::Failed,
+                            ["Streaming stopped, reason: {:?}", flow]
+                        );
+                    }
+                }
+
+                self.sinkpad.pause_task().unwrap();
+            }
+        }
+    }
+
     fn sink_chain(
         &self,
         pad: &gst::Pad,
@@ -320,6 +769,23 @@ impl SccParse {
         self.handle_buffer(element, Some(buffer))
     }
 
+    fn flush(&self, mut state: MutexGuard<State>) -> MutexGuard<State> {
+        state.reader.clear();
+        state.parser.reset();
+        if let Some(pull) = &mut state.pull {
+            pull.offset = 0;
+        }
+        state.segment = gst::FormattedSegment::<gst::ClockTime>::new();
+        state.need_segment = true;
+        state.pending_events.clear();
+        state.last_position = 0.into();
+        state.last_timecode = None;
+
+        drop(state);
+
+        self.state.lock().unwrap()
+    }
+
     fn sink_event(&self, pad: &gst::Pad, element: &super::SccParse, event: gst::Event) -> bool {
         use gst::EventView;
 
@@ -337,13 +803,9 @@ impl SccParse {
                 true
             }
             EventView::FlushStop(_) => {
-                let mut state = self.state.lock().unwrap();
-                state.reader.clear();
-                state.parser.reset();
-                state.need_segment = true;
-                state.pending_events.clear();
-                state.last_position = gst::ClockTime::from_seconds(0);
-                state.last_timecode = None;
+                let state = self.state.lock().unwrap();
+                let state = self.flush(state);
+                drop(state);
 
                 pad.event_default(Some(element), event)
             }
@@ -370,15 +832,105 @@ impl SccParse {
         }
     }
 
+    fn perform_seek(&self, event: &gst::event::Seek, element: &super::SccParse) -> bool {
+        let mut state = self.state.lock().unwrap();
+
+        if state.pull.is_none() {
+            gst_error!(CAT, obj: element, "seeking is only supported in pull mode");
+            return false;
+        }
+
+        let (rate, flags, start_type, start, stop_type, stop) = event.get();
+
+        let mut start: gst::ClockTime = match start.try_into() {
+            Ok(start) => start,
+            Err(_) => {
+                gst_error!(CAT, obj: element, "seek has invalid format");
+                return false;
+            }
+        };
+
+        let mut stop: gst::ClockTime = match stop.try_into() {
+            Ok(stop) => stop,
+            Err(_) => {
+                gst_error!(CAT, obj: element, "seek has invalid format");
+                return false;
+            }
+        };
+
+        if !flags.contains(gst::SeekFlags::FLUSH) {
+            gst_error!(CAT, obj: element, "only flushing seeks are supported");
+            return false;
+        }
+
+        if start_type == gst::SeekType::End || stop_type == gst::SeekType::End {
+            gst_error!(CAT, obj: element, "Relative seeks are not supported");
+            return false;
+        }
+
+        let pull = state.pull.as_ref().unwrap();
+
+        if start_type == gst::SeekType::Set {
+            start = start.min(pull.duration).unwrap_or(start);
+        }
+
+        if stop_type == gst::SeekType::Set {
+            stop = stop.min(pull.duration).unwrap_or(stop);
+        }
+
+        state.seeking = true;
+        let seek_seqnum = event.get_seqnum();
+        state.seek_seqnum = Some(seek_seqnum);
+
+        let event = gst::event::FlushStart::builder()
+            .seqnum(seek_seqnum)
+            .build();
+
+        gst_debug!(CAT, obj: element, "Sending event {:?} upstream", event);
+        self.sinkpad.push_event(event);
+
+        let event = gst::event::FlushStart::builder()
+            .seqnum(seek_seqnum)
+            .build();
+
+        gst_debug!(CAT, obj: element, "Pushing event {:?}", event);
+        self.srcpad.push_event(event);
+
+        self.sinkpad.pause_task().unwrap();
+
+        state = self.flush(state);
+
+        let event = gst::event::FlushStop::builder(true)
+            .seqnum(seek_seqnum)
+            .build();
+
+        /* Drop our state while we push a serialized event upstream */
+        drop(state);
+
+        gst_debug!(CAT, obj: element, "Sending event {:?} upstream", event);
+        self.sinkpad.push_event(event);
+
+        state = self.state.lock().unwrap();
+
+        state
+            .segment
+            .do_seek(rate, flags, start_type, start, stop_type, stop);
+
+        match self.start_task(element) {
+            Err(error) => {
+                error.log();
+                false
+            }
+            _ => true,
+        }
+    }
+
     fn src_event(&self, pad: &gst::Pad, element: &super::SccParse, event: gst::Event) -> bool {
         use gst::EventView;
 
         gst_log!(CAT, obj: pad, "Handling event {:?}", event);
         match event.view() {
-            EventView::Seek(_) => {
-                gst_log!(CAT, obj: pad, "Dropping seek event");
-                false
-            }
+            EventView::Seek(e) => self.perform_seek(&e, element),
             _ => pad.event_default(Some(element), event),
         }
     }
@@ -395,14 +947,24 @@ impl SccParse {
 
         match query.view_mut() {
             QueryView::Seeking(mut q) => {
-                // We don't support any seeking at all
+                let state = self.state.lock().unwrap();
+
                 let fmt = q.get_format();
-                q.set(
-                    false,
-                    gst::GenericFormattedValue::Other(fmt, -1),
-                    gst::GenericFormattedValue::Other(fmt, -1),
-                );
-                true
+
+                if fmt == gst::Format::Time {
+                    if let Some(pull) = state.pull.as_ref() {
+                        q.set(
+                            true,
+                            gst::GenericFormattedValue::Time(0.into()),
+                            gst::GenericFormattedValue::Time(pull.duration),
+                        );
+                        true
+                    } else {
+                        false
+                    }
+                } else {
+                    false
+                }
             }
             QueryView::Position(ref mut q) => {
                 // For Time answer ourselfs, otherwise forward
@@ -414,6 +976,24 @@ impl SccParse {
                     self.sinkpad.peer_query(query)
                 }
             }
+            QueryView::Duration(ref mut q) => {
+                // For Time answer ourselfs, otherwise forward
+                let state = self.state.lock().unwrap();
+                if q.get_format() == gst::Format::Time {
+                    if let Some(pull) = state.pull.as_ref() {
+                        if pull.duration.is_some() {
+                            q.set(state.pull.as_ref().unwrap().duration);
+                            true
+                        } else {
+                            false
+                        }
+                    } else {
+                        false
+                    }
+                } else {
+                    self.sinkpad.peer_query(query)
+                }
+            }
             _ => pad.query_default(Some(element), query),
         }
     }
@@ -431,6 +1011,25 @@ impl ObjectSubclass for SccParse {
     fn with_class(klass: &Self::Class) -> Self {
         let templ = klass.get_pad_template("sink").unwrap();
         let sinkpad = gst::Pad::builder_with_template(&templ, Some("sink"))
+            .activate_function(|pad, parent| {
+                SccParse::catch_panic_pad_function(
+                    parent,
+                    || Err(gst_loggable_error!(CAT, "Panic activating sink pad")),
+                    |parse, element| parse.sink_activate(pad, element),
+                )
+            })
+            .activatemode_function(|pad, parent, mode, active| {
+                SccParse::catch_panic_pad_function(
+                    parent,
+                    || {
+                        Err(gst_loggable_error!(
+                            CAT,
+                            "Panic activating sink pad with mode"
+                        ))
+                    },
+                    |parse, element| parse.sink_activatemode(pad, element, mode, active),
+                )
+            })
             .chain_function(|pad, parent, buffer| {
                 SccParse::catch_panic_pad_function(
                     parent,
diff --git a/video/closedcaption/src/scc_parse/parser.rs b/video/closedcaption/src/scc_parse/parser.rs
index b1b77cd79..53ccd4e8f 100644
--- a/video/closedcaption/src/scc_parse/parser.rs
+++ b/video/closedcaption/src/scc_parse/parser.rs
@@ -141,6 +141,12 @@ impl SccParser {
         }
     }
 
+    pub fn new_scan_captions() -> Self {
+        Self {
+            state: State::CaptionOrEmpty,
+        }
+    }
+
     pub fn reset(&mut self) {
         self.state = State::Header;
     }
diff --git a/video/closedcaption/tests/scc_parse.rs b/video/closedcaption/tests/scc_parse.rs
index 3e0a449f8..b960866eb 100644
--- a/video/closedcaption/tests/scc_parse.rs
+++ b/video/closedcaption/tests/scc_parse.rs
@@ -17,10 +17,12 @@
 // Boston, MA 02110-1335, USA.
 
 use gst::prelude::*;
+use gst::EventView;
 use gst_video::{ValidVideoTimeCode, VideoTimeCode};
 use pretty_assertions::assert_eq;
 use rand::{Rng, SeedableRng};
 use std::collections::VecDeque;
+use std::path::PathBuf;
 
 fn init() {
     use std::sync::Once;
@@ -199,3 +201,83 @@ fn test_timecodes() {
             .build()
     );
 }
+
+#[test]
+fn test_pull() {
+    init();
+
+    let mut path = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    path.push("tests/dn2018-1217.scc");
+
+    let mut h = gst_check::Harness::new_parse(&format!("filesrc location={:?} ! sccparse", path));
+
+    h.play();
+
+    /* Let's first pull until EOS */
+    loop {
+        let mut done = false;
+
+        while h.events_in_queue() != 0 {
+            let event = h.pull_event();
+
+            if let Ok(event) = event {
+                match event.view() {
+                    EventView::Eos(_) => {
+                        done = true;
+                        break;
+                    }
+                    _ => (),
+                }
+            }
+        }
+
+        while h.buffers_in_queue() != 0 {
+            let _ = h.pull();
+        }
+
+        if done {
+            break;
+        }
+    }
+
+    /* Now seek and check that we receive buffers with appropriate PTS */
+    h.push_upstream_event(gst::event::Seek::new(
+        1.0,
+        gst::SeekFlags::FLUSH,
+        gst::SeekType::Set,
+        gst::GenericFormattedValue::Time(18 * gst::SECOND),
+        gst::SeekType::Set,
+        gst::GenericFormattedValue::Time(19 * gst::SECOND),
+    ));
+
+    loop {
+        let mut done = false;
+
+        while h.buffers_in_queue() != 0 {
+            if let Ok(buffer) = h.pull() {
+                let pts = buffer.get_pts();
+                let end_time = pts + buffer.get_duration();
+
+                assert!(end_time >= 18 * gst::SECOND && pts < 19 * gst::SECOND);
+            }
+        }
+
+        while h.events_in_queue() != 0 {
+            let event = h.pull_event();
+
+            if let Ok(event) = event {
+                match event.view() {
+                    EventView::Eos(_) => {
+                        done = true;
+                        break;
+                    }
+                    _ => (),
+                }
+            }
+        }
+
+        if done {
+            break;
+        }
+    }
+}