playback: fix error 404 when seeking before start of segment (#4276) (#4533) (#4539)

Fixes #4276
Replaces #4533

Author: aler9

internal/playback/muxer_fmp4.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/fmp4"
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/fmp4/seekablebuffer"
+	"github.com/bluenviron/mediamtx/internal/recordstore"
 )
 
 const (
@@ -75,7 +76,7 @@ func (w *muxerFMP4) writeSample(
 
 			// if sample is a IDR, remove previous GOP
 			if !isNonSyncSample {
-				w.curTrack.samples = nil
+				w.curTrack.samples = w.curTrack.samples[:0]
 			}
 		} else {
 			diff := dts - w.curTrack.lastDTS
@@ -103,10 +104,11 @@ func (w *muxerFMP4) writeSample(
 	} else {
 		if !isNonSyncSample { // sample is IDR
 			// reset GOP
-			w.curTrack.samples = []*fmp4.Sample{{
+			w.curTrack.samples = w.curTrack.samples[:0]
+			w.curTrack.samples = append(w.curTrack.samples, &fmp4.Sample{
 				IsNonSyncSample: isNonSyncSample,
 				Payload:         pl,
-			}}
+			})
 		} else { // sample is not IDR
 			// append sample to current GOP, with PTSOffset = 0 and Duration = 0
 			w.curTrack.samples = append(w.curTrack.samples, &fmp4.Sample{
@@ -120,7 +122,7 @@ func (w *muxerFMP4) writeSample(
 }
 
 func (w *muxerFMP4) writeFinalDTS(dts int64) {
-	if w.curTrack.firstDTS >= 0 {
+	if len(w.curTrack.samples) != 0 && w.curTrack.firstDTS >= 0 {
 		diff := dts - w.curTrack.lastDTS
 		if diff < 0 {
 			diff = 0
@@ -156,26 +158,20 @@ func (w *muxerFMP4) innerFlush(final bool) error {
 		}
 	}
 
-	if part.Tracks != nil {
-		part.SequenceNumber = w.nextSequenceNumber
-		w.nextSequenceNumber++
-
+	// no samples to write
+	if part.Tracks == nil {
+		// if no samples has been written before, return an error
 		if w.init != nil {
-			err := w.init.Marshal(&w.outBuf)
-			if err != nil {
-				return err
-			}
-
-			_, err = w.w.Write(w.outBuf.Bytes())
-			if err != nil {
-				return err
-			}
-
-			w.init = nil
-			w.outBuf.Reset()
+			return recordstore.ErrNoSegmentsFound
 		}
+		return nil
+	}
+
+	part.SequenceNumber = w.nextSequenceNumber
+	w.nextSequenceNumber++
 
-		err := part.Marshal(&w.outBuf)
+	if w.init != nil {
+		err := w.init.Marshal(&w.outBuf)
 		if err != nil {
 			return err
 		}
@@ -185,9 +181,22 @@ func (w *muxerFMP4) innerFlush(final bool) error {
 			return err
 		}
 
+		w.init = nil
 		w.outBuf.Reset()
 	}
 
+	err := part.Marshal(&w.outBuf)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.w.Write(w.outBuf.Bytes())
+	if err != nil {
+		return err
+	}
+
+	w.outBuf.Reset()
+
 	return nil
 }
 

internal/playback/muxer_mp4.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/fmp4"
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/pmp4"
+	"github.com/bluenviron/mediamtx/internal/recordstore"
 )
 
 type muxerMP4Track struct {
@@ -55,17 +56,17 @@ func (w *muxerMP4) writeSample(
 ) error {
 	// remove GOPs before the GOP of the first sample
 	if (dts < 0 || (dts >= 0 && w.curTrack.lastDTS < 0)) && !isNonSyncSample {
-		w.curTrack.Samples = nil
+		w.curTrack.Samples = w.curTrack.Samples[:0]
 	}
 
-	if w.curTrack.Samples == nil {
+	if len(w.curTrack.Samples) == 0 {
 		w.curTrack.TimeOffset = int32(dts)
 	} else {
-		diff := dts - w.curTrack.lastDTS
-		if diff < 0 {
-			diff = 0
+		duration := dts - w.curTrack.lastDTS
+		if duration < 0 {
+			duration = 0
 		}
-		w.curTrack.Samples[len(w.curTrack.Samples)-1].Duration = uint32(diff)
+		w.curTrack.Samples[len(w.curTrack.Samples)-1].Duration = uint32(duration)
 	}
 
 	// prevent warning "edit list: 1 Missing key frame while searching for timestamp: 0"
@@ -85,14 +86,20 @@ func (w *muxerMP4) writeSample(
 }
 
 func (w *muxerMP4) writeFinalDTS(dts int64) {
-	diff := dts - w.curTrack.lastDTS
-	if diff < 0 {
-		diff = 0
+	if len(w.curTrack.Samples) != 0 {
+		duration := dts - w.curTrack.lastDTS
+		if duration < 0 {
+			duration = 0
+		}
+		w.curTrack.Samples[len(w.curTrack.Samples)-1].Duration = uint32(duration)
 	}
-	w.curTrack.Samples[len(w.curTrack.Samples)-1].Duration = uint32(diff)
 }
 
 func (w *muxerMP4) flush() error {
+	if len(w.curTrack.Samples) == 0 || w.curTrack.lastDTS < 0 {
+		return recordstore.ErrNoSegmentsFound
+	}
+
 	h := pmp4.Presentation{
 		Tracks: make([]*pmp4.Track, len(w.tracks)),
 	}

internal/playback/on_get.go

@@ -64,9 +64,9 @@ func seekAndMux(
 
 		m.writeInit(firstInit)
 
-		segmentStartOffset := start.Sub(segments[0].Start)
+		segmentStartOffset := segments[0].Start.Sub(start) // this is negative
 
-		segmentDuration, err := segmentFMP4SeekAndMuxParts(f, segmentStartOffset, duration, firstInit, m)
+		segmentDuration, err := segmentFMP4MuxParts(f, segmentStartOffset, duration, firstInit, m)
 		if err != nil {
 			return err
 		}
@@ -90,7 +90,7 @@ func seekAndMux(
 				break
 			}
 
-			segmentStartOffset := seg.Start.Sub(start)
+			segmentStartOffset := seg.Start.Sub(start) // this is positive
 
 			var segmentDuration time.Duration
 			segmentDuration, err = segmentFMP4MuxParts(f, segmentStartOffset, duration, firstInit, m)