mediamtx/internal/hls/muxer.go

package hls

import (
	"io"
	"time"

	"github.com/aler9/gortsplib"

	"github.com/aler9/rtsp-simple-server/internal/h264"
)

const (
	// an offset between PCR and PTS/DTS is needed to avoid PCR > PTS
	pcrOffset = 500 * time.Millisecond

	segmentMinAUCount = 100
)

// Muxer is a HLS muxer.
type Muxer struct {
	hlsSegmentCount    int
	hlsSegmentDuration time.Duration
	videoTrack         *gortsplib.Track
	audioTrack         *gortsplib.Track

	h264Conf        *gortsplib.TrackConfigH264
	aacConf         *gortsplib.TrackConfigAAC
	videoDTSEst     *h264.DTSEstimator
	audioAUCount    int
	currentSegment  *segment
	startPCR        time.Time
	startPTS        time.Duration
	primaryPlaylist *primaryPlaylist
	streamPlaylist  *streamPlaylist
}

// NewMuxer allocates a Muxer.
func NewMuxer(
	hlsSegmentCount int,
	hlsSegmentDuration time.Duration,
	videoTrack *gortsplib.Track,
	audioTrack *gortsplib.Track) (*Muxer, error) {
	var h264Conf *gortsplib.TrackConfigH264
	if videoTrack != nil {
		var err error
		h264Conf, err = videoTrack.ExtractConfigH264()
		if err != nil {
			return nil, err
		}
	}

	var aacConf *gortsplib.TrackConfigAAC
	if audioTrack != nil {
		var err error
		aacConf, err = audioTrack.ExtractConfigAAC()
		if err != nil {
			return nil, err
		}
	}

	m := &Muxer{
		hlsSegmentCount:    hlsSegmentCount,
		hlsSegmentDuration: hlsSegmentDuration,
		videoTrack:         videoTrack,
		audioTrack:         audioTrack,
		h264Conf:           h264Conf,
		aacConf:            aacConf,
		currentSegment:     newSegment(videoTrack, audioTrack, h264Conf, aacConf),
		primaryPlaylist:    newPrimaryPlaylist(videoTrack, audioTrack, h264Conf),
		streamPlaylist:     newStreamPlaylist(hlsSegmentCount),
	}

	return m, nil
}

// Close closes a Muxer.
func (m *Muxer) Close() {
	m.streamPlaylist.close()
}

// WriteH264 writes H264 NALUs, grouped by PTS, into the muxer.
func (m *Muxer) WriteH264(pts time.Duration, nalus [][]byte) error {
	idrPresent := func() bool {
		for _, nalu := range nalus {
			typ := h264.NALUType(nalu[0] & 0x1F)
			if typ == h264.NALUTypeIDR {
				return true
			}
		}
		return false
	}()

	// skip group silently until we find one with a IDR
	if !m.currentSegment.firstPacketWritten && !idrPresent {
		return nil
	}

	if m.currentSegment.firstPacketWritten {
		if idrPresent &&
			m.currentSegment.duration() >= m.hlsSegmentDuration {
			m.streamPlaylist.pushSegment(m.currentSegment)

			m.currentSegment = newSegment(m.videoTrack, m.audioTrack, m.h264Conf, m.aacConf)
			m.currentSegment.setStartPCR(m.startPCR)
		}
	} else {
		m.startPCR = time.Now()
		m.startPTS = pts
		m.currentSegment.setStartPCR(m.startPCR)
		m.videoDTSEst = h264.NewDTSEstimator()
	}

	pts -= m.startPTS

	err := m.currentSegment.writeH264(
		m.videoDTSEst.Feed(pts)+pcrOffset,
		pts+pcrOffset,
		idrPresent,
		nalus)
	if err != nil {
		return err
	}

	return nil
}

// WriteAAC writes AAC AUs, grouped by PTS, into the muxer.
func (m *Muxer) WriteAAC(pts time.Duration, aus [][]byte) error {
	if m.videoTrack == nil {
		if m.currentSegment.firstPacketWritten {
			if m.audioAUCount >= segmentMinAUCount &&
				m.currentSegment.duration() >= m.hlsSegmentDuration {
				m.audioAUCount = 0

				m.streamPlaylist.pushSegment(m.currentSegment)

				m.currentSegment = newSegment(m.videoTrack, m.audioTrack, m.h264Conf, m.aacConf)
				m.currentSegment.setStartPCR(m.startPCR)
			}
		} else {
			m.startPCR = time.Now()
			m.startPTS = pts
			m.currentSegment.setStartPCR(m.startPCR)
		}
	} else {
		if !m.currentSegment.firstPacketWritten {
			return nil
		}
	}

	pts = pts - m.startPTS + pcrOffset

	for _, au := range aus {
		err := m.currentSegment.writeAAC(pts, au)
		if err != nil {
			return err
		}

		if m.videoTrack == nil {
			m.audioAUCount++
		}

		pts += 1000 * time.Second / time.Duration(m.aacConf.SampleRate)
	}

	return nil
}

// PrimaryPlaylist returns a reader to read the primary playlist
func (m *Muxer) PrimaryPlaylist() io.Reader {
	return m.primaryPlaylist.reader()
}

// StreamPlaylist returns a reader to read the stream playlist.
func (m *Muxer) StreamPlaylist() io.Reader {
	return m.streamPlaylist.reader()
}

// Segment returns a reader to read a segment.
func (m *Muxer) Segment(fname string) io.Reader {
	return m.streamPlaylist.segment(fname)
}