fmp4mux: Dequeue the earliest buffer from any pad first instead of dequeueing up to a whole fragment from the same pad

This keeps the fill levels of each sinkpad in sync.

generic/fmp4/src/fmp4mux/imp.rs

@@ -179,6 +179,94 @@ pub(crate) struct FMP4Mux {
 }
 
 impl FMP4Mux {
+    fn find_earliest_stream<'a>(
+        &self,
+        element: &super::FMP4Mux,
+        state: &'a mut State,
+        timeout: bool,
+    ) -> Result<Option<(usize, &'a mut Stream)>, gst::FlowError> {
+        let mut earliest_stream = None;
+        let mut all_have_data_or_eos = true;
+
+        for (idx, stream) in state.streams.iter_mut().enumerate() {
+            let buffer = match stream.sinkpad.peek_buffer() {
+                Some(buffer) => buffer,
+                None => {
+                    if stream.sinkpad.is_eos() {
+                        gst::trace!(CAT, obj: &stream.sinkpad, "Stream is EOS");
+                    } else {
+                        all_have_data_or_eos = false;
+                        gst::trace!(CAT, obj: &stream.sinkpad, "Stream has no buffer");
+                    }
+                    continue;
+                }
+            };
+
+            if stream.fragment_filled {
+                gst::trace!(CAT, obj: &stream.sinkpad, "Stream has current fragment filled");
+                continue;
+            }
+
+            let segment = match stream
+                .sinkpad
+                .segment()
+                .clone()
+                .downcast::<gst::ClockTime>()
+                .ok()
+            {
+                Some(segment) => segment,
+                None => {
+                    gst::error!(CAT, obj: &stream.sinkpad, "Got buffer before segment");
+                    return Err(gst::FlowError::Error);
+                }
+            };
+
+            // If the stream has no valid running time, assume it's before everything else.
+            let running_time = match segment.to_running_time(buffer.dts_or_pts()) {
+                None => {
+                    gst::trace!(CAT, obj: &stream.sinkpad, "Stream has no valid running time");
+                    if earliest_stream.is_none() {
+                        earliest_stream = Some((idx, stream, gst::ClockTime::ZERO));
+                    }
+                    continue;
+                }
+                Some(running_time) => running_time,
+            };
+
+            gst::trace!(CAT, obj: &stream.sinkpad, "Stream has running time {} queued", running_time);
+
+            if earliest_stream
+                .as_ref()
+                .map_or(true, |(_idx, _stream, earliest_running_time)| {
+                    *earliest_running_time > running_time
+                })
+            {
+                earliest_stream = Some((idx, stream, running_time));
+            }
+        }
+
+        if !timeout && !all_have_data_or_eos {
+            gst::trace!(
+                CAT,
+                obj: element,
+                "No timeout and not all streams have a buffer or are EOS"
+            );
+            Ok(None)
+        } else if let Some((idx, stream, earliest_running_time)) = earliest_stream {
+            gst::trace!(
+                CAT,
+                obj: element,
+                "Stream {} is earliest stream with running time {}",
+                stream.sinkpad.name(),
+                earliest_running_time
+            );
+            Ok(Some((idx, stream)))
+        } else {
+            gst::trace!(CAT, obj: element, "No streams have data queued currently");
+            Ok(None)
+        }
+    }
+
     // Queue incoming buffers as individual GOPs.
     fn queue_gops(
         &self,
@@ -1831,9 +1919,9 @@ impl AggregatorImpl for FMP4Mux {
     ) -> Result<gst::FlowSuccess, gst::FlowError> {
         let settings = self.settings.lock().unwrap().clone();
 
-        let mut all_eos = true;
         let mut upstream_events = vec![];
 
+        let all_eos;
         let (caps, buffers) = {
             let mut state = self.state.lock().unwrap();
 
@@ -1843,23 +1931,21 @@ impl AggregatorImpl for FMP4Mux {
             }
 
             // Queue buffers from all streams that are not filled for the current fragment yet
+            //
+            // Always take a buffer from the stream with the earliest queued buffer to keep the
+            // fill-level at all sinkpads in sync.
             let fragment_start_pts = state.fragment_start_pts;
-            for (idx, stream) in state.streams.iter_mut().enumerate() {
-                if stream.fragment_filled {
-                    let buffer = stream.sinkpad.peek_buffer();
-                    all_eos &= buffer.is_none() && stream.sinkpad.is_eos();
 
-                    continue;
-                }
-
-                let buffer = stream.sinkpad.pop_buffer();
-                all_eos &= buffer.is_none() && stream.sinkpad.is_eos();
-
-                let buffer = match buffer {
-                    None => continue,
+            while let Some((idx, stream)) =
+                self.find_earliest_stream(aggregator, &mut state, timeout)?
+            {
+                // Can only happen if the stream was flushed in the meantime
+                let buffer = match stream.sinkpad.pop_buffer() {
                     Some(buffer) => buffer,
+                    None => continue,
                 };
 
+                // Can only happen if the stream was flushed in the meantime
                 let segment = match stream
                     .sinkpad
                     .segment()
@@ -1907,10 +1993,6 @@ impl AggregatorImpl for FMP4Mux {
                 }
             }
 
-            if all_eos {
-                gst::debug!(CAT, obj: aggregator, "All streams are EOS now");
-            }
-
             // Calculate the earliest PTS after queueing input if we can now.
             if state.earliest_pts.is_none() {
                 let mut earliest_pts = None;
@@ -1969,6 +2051,11 @@ impl AggregatorImpl for FMP4Mux {
                 }
             }
 
+            all_eos = state.streams.iter().all(|stream| stream.sinkpad.is_eos());
+            if all_eos {
+                gst::debug!(CAT, obj: aggregator, "All streams are EOS now");
+            }
+
             // If enough GOPs were queued, drain and create the output fragment
             self.drain(aggregator, &mut state, &settings, timeout, all_eos)?
         };

generic/fmp4/tests/tests.rs

@@ -551,7 +551,6 @@ fn test_live_timeout() {
             if j == 1 && i == 4 {
                 // Advance time and crank the clock another time. This brings us at the end of the
                 // EOS.
-                h1.set_time(gst::ClockTime::from_seconds(7)).unwrap();
                 h1.crank_single_clock_wait().unwrap();
                 continue;
             }
@@ -652,6 +651,8 @@ fn test_gap_events() {
     let mut h1 = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
     let mut h2 = gst_check::Harness::with_element(&h1.element().unwrap(), Some("sink_1"), None);
 
+    h1.use_testclock();
+
     // 5s fragment duration
     h1.element()
         .unwrap()
@@ -760,6 +761,10 @@ fn test_gap_events() {
         }
     }
 
+    // Advance time and crank the clock: this should bring us to the end of the first fragment
+    h1.set_time(gst::ClockTime::from_seconds(5)).unwrap();
+    h1.crank_single_clock_wait().unwrap();
+
     let header = h1.pull().unwrap();
     assert_eq!(
         header.flags(),