mediamtx/internal/playback/muxer_mp4.go

package playback

import (
	"io"

	"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 {
	pmp4.Track
	lastDTS int64
}

func findTrackMP4(tracks []*muxerMP4Track, id int) *muxerMP4Track {
	for _, track := range tracks {
		if track.ID == id {
			return track
		}
	}
	return nil
}

type muxerMP4 struct {
	w io.Writer

	tracks   []*muxerMP4Track
	curTrack *muxerMP4Track
}

func (w *muxerMP4) writeInit(init *fmp4.Init) {
	w.tracks = make([]*muxerMP4Track, len(init.Tracks))

	for i, track := range init.Tracks {
		w.tracks[i] = &muxerMP4Track{
			Track: pmp4.Track{
				ID:        track.ID,
				TimeScale: track.TimeScale,
				Codec:     track.Codec,
			},
		}
	}
}

func (w *muxerMP4) setTrack(trackID int) {
	w.curTrack = findTrackMP4(w.tracks, trackID)
}

func (w *muxerMP4) writeSample(
	dts int64,
	ptsOffset int32,
	isNonSyncSample bool,
	payloadSize uint32,
	getPayload func() ([]byte, error),
) error {
	// remove GOPs before the GOP of the first sample
	if (dts < 0 || (dts >= 0 && w.curTrack.lastDTS < 0)) && !isNonSyncSample {
		w.curTrack.Samples = w.curTrack.Samples[:0]
	}

	if len(w.curTrack.Samples) == 0 {
		w.curTrack.TimeOffset = int32(dts)
	} else {
		duration := max(dts-w.curTrack.lastDTS, 0)
		w.curTrack.Samples[len(w.curTrack.Samples)-1].Duration = uint32(duration)
	}

	// prevent warning "edit list: 1 Missing key frame while searching for timestamp: 0"
	if !isNonSyncSample {
		ptsOffset = 0
	}

	w.curTrack.Samples = append(w.curTrack.Samples, &pmp4.Sample{
		PTSOffset:       ptsOffset,
		IsNonSyncSample: isNonSyncSample,
		PayloadSize:     payloadSize,
		GetPayload:      getPayload,
	})
	w.curTrack.lastDTS = dts

	return nil
}

func (w *muxerMP4) writeFinalDTS(dts int64) {
	if len(w.curTrack.Samples) != 0 {
		duration := max(dts-w.curTrack.lastDTS, 0)
		w.curTrack.Samples[len(w.curTrack.Samples)-1].Duration = uint32(duration)
	}
}

func (w *muxerMP4) flush() error {
	if len(w.curTrack.Samples) == 0 || w.curTrack.lastDTS < 0 {
		return recordstore.ErrNoSegmentsFound
	}

	var tracks []*pmp4.Track
	for _, track := range w.tracks {
		if len(track.Samples) != 0 {
			tracks = append(tracks, &track.Track)
		}
	}

	h := pmp4.Presentation{
		Tracks: tracks,
	}

	return h.Marshal(w.w)
}