playaback: use a fixed fMP4 part duration

internal/playback/muxer.go

@@ -3,8 +3,7 @@ package playback
 type muxer interface {
 	writeInit(init []byte)
 	setTrack(trackID int)
-	writeSample(dts int64, ptsOffset int32, isNonSyncSample bool, payload []byte)
+	writeSample(dts int64, ptsOffset int32, isNonSyncSample bool, payload []byte) error
 	writeFinalDTS(dts int64)
 	flush() error
-	finalFlush() error
 }

internal/playback/muxer_fmp4.go

@@ -2,15 +2,17 @@ package playback
 
 import (
 	"io"
+	"time"
 
 	"github.com/bluenviron/mediacommon/pkg/formats/fmp4"
 	"github.com/bluenviron/mediacommon/pkg/formats/fmp4/seekablebuffer"
 )
 
+var partSize = durationGoToMp4(1*time.Second, fmp4Timescale)
+
 type muxerFMP4Track struct {
-	started  bool
 	id       int
-	firstDTS uint64
+	firstDTS int64
 	lastDTS  int64
 	samples  []*fmp4.PartSample
 }
@@ -42,58 +44,27 @@ func (w *muxerFMP4) setTrack(trackID int) {
 	w.curTrack = findTrack(w.tracks, trackID)
 	if w.curTrack == nil {
 		w.curTrack = &muxerFMP4Track{
-			id: trackID,
+			id:       trackID,
+			firstDTS: -1,
 		}
 		w.tracks = append(w.tracks, w.curTrack)
 	}
 }
 
-func (w *muxerFMP4) writeSample(dts int64, ptsOffset int32, isNonSyncSample bool, payload []byte) {
-	if !w.curTrack.started {
-		if dts >= 0 {
-			w.curTrack.started = true
-			w.curTrack.firstDTS = uint64(dts)
+func (w *muxerFMP4) writeSample(dts int64, ptsOffset int32, isNonSyncSample bool, payload []byte) error {
+	if dts >= 0 {
+		if w.curTrack.firstDTS < 0 {
+			w.curTrack.firstDTS = dts
 
+			// reset GOP preceding the first frame
 			if !isNonSyncSample {
-				w.curTrack.samples = []*fmp4.PartSample{{
-					PTSOffset:       ptsOffset,
-					IsNonSyncSample: isNonSyncSample,
-					Payload:         payload,
-				}}
-			} else {
-				w.curTrack.samples = append(w.curTrack.samples, &fmp4.PartSample{
-					PTSOffset:       ptsOffset,
-					IsNonSyncSample: isNonSyncSample,
-					Payload:         payload,
-				})
+				w.curTrack.samples = nil
 			}
-			w.curTrack.lastDTS = dts
-		} else {
-			ptsOffset = 0
-
-			if !isNonSyncSample {
-				w.curTrack.samples = []*fmp4.PartSample{{
-					PTSOffset:       ptsOffset,
-					IsNonSyncSample: isNonSyncSample,
-					Payload:         payload,
-				}}
-			} else {
-				w.curTrack.samples = append(w.curTrack.samples, &fmp4.PartSample{
-					PTSOffset:       ptsOffset,
-					IsNonSyncSample: isNonSyncSample,
-					Payload:         payload,
-				})
-			}
-		}
-	} else {
-		if w.curTrack.samples == nil {
-			w.curTrack.firstDTS = uint64(dts)
 		} else {
 			diff := dts - w.curTrack.lastDTS
 			if diff < 0 {
 				diff = 0
 			}
-
 			w.curTrack.samples[len(w.curTrack.samples)-1].Duration = uint32(diff)
 		}
 
@@ -103,25 +74,48 @@ func (w *muxerFMP4) writeSample(dts int64, ptsOffset int32, isNonSyncSample bool
 			Payload:         payload,
 		})
 		w.curTrack.lastDTS = dts
+
+		if (w.curTrack.lastDTS - w.curTrack.firstDTS) > int64(partSize) {
+			err := w.innerFlush(false)
+			if err != nil {
+				return err
+			}
+		}
+	} else {
+		// store GOP preceding the first frame, with PTSOffset = 0 and Duration = 0
+		if !isNonSyncSample {
+			w.curTrack.samples = []*fmp4.PartSample{{
+				IsNonSyncSample: isNonSyncSample,
+				Payload:         payload,
+			}}
+		} else {
+			w.curTrack.samples = append(w.curTrack.samples, &fmp4.PartSample{
+				IsNonSyncSample: isNonSyncSample,
+				Payload:         payload,
+			})
+		}
 	}
+
+	return nil
 }
 
 func (w *muxerFMP4) writeFinalDTS(dts int64) {
-	if w.curTrack.started && w.curTrack.samples != nil {
+	if w.curTrack.firstDTS >= 0 {
 		diff := dts - w.curTrack.lastDTS
 		if diff < 0 {
 			diff = 0
 		}
-
 		w.curTrack.samples[len(w.curTrack.samples)-1].Duration = uint32(diff)
 	}
 }
 
-func (w *muxerFMP4) flush2(final bool) error {
+func (w *muxerFMP4) innerFlush(final bool) error {
 	var part fmp4.Part
 
 	for _, track := range w.tracks {
-		if track.started && (len(track.samples) > 1 || (final && len(track.samples) != 0)) {
+		if track.firstDTS >= 0 && (len(track.samples) > 1 || (final && len(track.samples) != 0)) {
+			// do not write the final sample
+			// in order to allow changing its duration to compensate NTP-DTS differences
 			var samples []*fmp4.PartSample
 			if !final {
 				samples = track.samples[:len(track.samples)-1]
@@ -131,15 +125,13 @@ func (w *muxerFMP4) flush2(final bool) error {
 
 			part.Tracks = append(part.Tracks, &fmp4.PartTrack{
 				ID:       track.id,
-				BaseTime: track.firstDTS,
+				BaseTime: uint64(track.firstDTS),
 				Samples:  samples,
 			})
 
 			if !final {
 				track.samples = track.samples[len(track.samples)-1:]
-				track.firstDTS = uint64(track.lastDTS)
-			} else {
-				track.samples = nil
+				track.firstDTS = track.lastDTS
 			}
 		}
 	}
@@ -173,9 +165,5 @@ func (w *muxerFMP4) flush2(final bool) error {
 }
 
 func (w *muxerFMP4) flush() error {
-	return w.flush2(false)
-}
-
-func (w *muxerFMP4) finalFlush() error {
-	return w.flush2(true)
+	return w.innerFlush(true)
 }

internal/playback/on_get.go

@@ -110,14 +110,13 @@ func seekAndMux(
 			}()
 			if err != nil {
 				if errors.Is(err, errStopIteration) {
-					return nil
+					break
 				}
-
 				return err
 			}
 		}
 
-		err = m.finalFlush()
+		err = m.flush()
 		if err != nil {
 			return err
 		}

internal/playback/on_get_test.go

@@ -229,6 +229,7 @@ func TestOnGet(t *testing.T) {
 
 	writeSegment1(t, filepath.Join(dir, "mypath", "2008-11-07_11-22-00-500000.mp4"))
 	writeSegment2(t, filepath.Join(dir, "mypath", "2008-11-07_11-23-02-500000.mp4"))
+	writeSegment2(t, filepath.Join(dir, "mypath", "2008-11-07_11-23-04-500000.mp4"))
 
 	s := &Server{
 		Address:     "127.0.0.1:9996",
@@ -252,7 +253,7 @@ func TestOnGet(t *testing.T) {
 	v := url.Values{}
 	v.Set("path", "mypath")
 	v.Set("start", time.Date(2008, 11, 0o7, 11, 23, 1, 500000000, time.Local).Format(time.RFC3339Nano))
-	v.Set("duration", "2")
+	v.Set("duration", "3")
 	v.Set("format", "fmp4")
 	u.RawQuery = v.Encode()
 
@@ -283,36 +284,29 @@ func TestOnGet(t *testing.T) {
 							Duration: 0,
 							Payload:  []byte{3, 4},
 						},
-					},
-				},
-			},
-		},
-		{
-			SequenceNumber: 1,
-			Tracks: []*fmp4.PartTrack{
-				{
-					ID:       1,
-					BaseTime: 0,
-					Samples: []*fmp4.PartSample{
 						{
 							Duration:        90000,
 							IsNonSyncSample: true,
 							Payload:         []byte{5, 6},
 						},
+						{
+							Duration: 90000,
+							Payload:  []byte{7, 8},
+						},
 					},
 				},
 			},
 		},
 		{
-			SequenceNumber: 2,
+			SequenceNumber: 1,
 			Tracks: []*fmp4.PartTrack{
 				{
 					ID:       1,
-					BaseTime: 90000,
+					BaseTime: 180000,
 					Samples: []*fmp4.PartSample{
 						{
 							Duration: 90000,
-							Payload:  []byte{7, 8},
+							Payload:  []byte{9, 10},
 						},
 					},
 				},
@@ -385,6 +379,11 @@ func TestOnGetDifferentInit(t *testing.T) {
 							Duration: 0,
 							Payload:  []byte{3, 4},
 						},
+						{
+							Duration:        90000,
+							IsNonSyncSample: true,
+							Payload:         []byte{5, 6},
+						},
 					},
 				},
 			},
@@ -456,17 +455,6 @@ func TestOnGetNTPCompensation(t *testing.T) {
 							Duration: 0,
 							Payload:  []byte{3, 4},
 						},
-					},
-				},
-			},
-		},
-		{
-			SequenceNumber: 1,
-			Tracks: []*fmp4.PartTrack{
-				{
-					ID:       1,
-					BaseTime: 0,
-					Samples: []*fmp4.PartSample{
 						{
 							Duration:        45000, // 90 - 45
 							IsNonSyncSample: true,
@@ -481,11 +469,11 @@ func TestOnGetNTPCompensation(t *testing.T) {
 			},
 		},
 		{
-			SequenceNumber: 2,
+			SequenceNumber: 1,
 			Tracks: []*fmp4.PartTrack{
 				{
 					ID:       1,
-					BaseTime: 135000, // 180 - 45
+					BaseTime: 135000,
 					Samples: []*fmp4.PartSample{
 						{
 							Duration: 90000,

internal/playback/segment_fmp4.go

@@ -374,12 +374,15 @@ func segmentFMP4SeekAndMuxParts(
 					return nil, err
 				}
 
-				m.writeSample(
+				err = m.writeSample(
 					muxerDTS,
 					e.SampleCompositionTimeOffsetV1,
 					(e.SampleFlags&sampleFlagIsNonSyncSample) != 0,
 					payload,
 				)
+				if err != nil {
+					return nil, err
+				}
 
 				muxerDTS += int64(e.SampleDuration)
 			}
@@ -389,12 +392,6 @@ func segmentFMP4SeekAndMuxParts(
 			if muxerDTS > maxMuxerDTS {
 				maxMuxerDTS = muxerDTS
 			}
-
-		case "mdat":
-			err := m.flush()
-			if err != nil {
-				return nil, err
-			}
 		}
 		return nil, nil
 	})
@@ -474,12 +471,15 @@ func segmentFMP4WriteParts(
 					return nil, err
 				}
 
-				m.writeSample(
+				err = m.writeSample(
 					muxerDTS,
 					e.SampleCompositionTimeOffsetV1,
 					(e.SampleFlags&sampleFlagIsNonSyncSample) != 0,
 					payload,
 				)
+				if err != nil {
+					return nil, err
+				}
 
 				muxerDTS += int64(e.SampleDuration)
 			}
@@ -489,12 +489,6 @@ func segmentFMP4WriteParts(
 			if muxerDTS > maxMuxerDTS {
 				maxMuxerDTS = muxerDTS
 			}
-
-		case "mdat":
-			err := m.flush()
-			if err != nil {
-				return nil, err
-			}
 		}
 		return nil, nil
 	})