convert Tracks into Medias and Formats (#155)

* split tracks from medias

* move tracks into dedicated package

* move media into dedicated package

* edit Medias.Marshal() in order to return SDP

* add medias.Find() and simplify examples

* improve coverage

* fix rebase errors

* replace TrackIDs with MediaIDs

* implement media-specific and track-specific callbacks for reading RTCP and RTP packets

* rename publish into record, read into play

* add v2 tag

* rename tracks into formats

examples/client-read-format-h264-save-to-disk/main.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"github.com/aler9/gortsplib/v2"
+	"github.com/aler9/gortsplib/v2/pkg/format"
+	"github.com/aler9/gortsplib/v2/pkg/url"
+	"github.com/pion/rtp"
+)
+
+// This example shows how to
+// 1. connect to a RTSP server
+// 2. check if there's a H264 media
+// 3. save the content of the H264 media into a file in MPEG-TS format
+
+func main() {
+	c := gortsplib.Client{}
+
+	// parse URL
+	u, err := url.Parse("rtsp://localhost:8554/mystream")
+	if err != nil {
+		panic(err)
+	}
+
+	// connect to the server
+	err = c.Start(u.Scheme, u.Host)
+	if err != nil {
+		panic(err)
+	}
+	defer c.Close()
+
+	// find published medias
+	medias, baseURL, _, err := c.Describe(u)
+	if err != nil {
+		panic(err)
+	}
+
+	// find the H264 media and format
+	var trak *format.H264
+	medi := medias.Find(&trak)
+	if medi == nil {
+		panic("media not found")
+	}
+
+	// setup RTP/H264->H264 decoder
+	rtpDec := trak.CreateDecoder()
+
+	// setup H264->MPEGTS muxer
+	mpegtsMuxer, err := newMPEGTSMuxer(trak.SafeSPS(), trak.SafePPS())
+	if err != nil {
+		panic(err)
+	}
+
+	// setup the chosen media only
+	_, err = c.Setup(medi, baseURL, 0, 0)
+	if err != nil {
+		panic(err)
+	}
+
+	// called when a RTP packet arrives
+	c.OnPacketRTP(medi, trak, func(pkt *rtp.Packet) {
+		// convert RTP packets into NALUs
+		nalus, pts, err := rtpDec.Decode(pkt)
+		if err != nil {
+			return
+		}
+
+		// encode H264 NALUs into MPEG-TS
+		mpegtsMuxer.encode(nalus, pts)
+	})
+
+	// start playing
+	_, err = c.Play(nil)
+	if err != nil {
+		panic(err)
+	}
+
+	// wait until a fatal error
+	panic(c.Wait())
+}

examples/client-read-format-h264-save-to-disk/mpegtsmuxer.go

@@ -0,0 +1,173 @@
+package main
+
+import (
+	"bufio"
+	"context"
+	"log"
+	"os"
+	"time"
+
+	"github.com/aler9/gortsplib/v2/pkg/h264"
+	"github.com/asticode/go-astits"
+)
+
+// mpegtsMuxer allows to save a H264 stream into a MPEG-TS file.
+type mpegtsMuxer struct {
+	sps []byte
+	pps []byte
+
+	f                *os.File
+	b                *bufio.Writer
+	mux              *astits.Muxer
+	dtsExtractor     *h264.DTSExtractor
+	firstIDRReceived bool
+	startDTS         time.Duration
+}
+
+// newMPEGTSMuxer allocates a mpegtsMuxer.
+func newMPEGTSMuxer(sps []byte, pps []byte) (*mpegtsMuxer, error) {
+	f, err := os.Create("mystream.ts")
+	if err != nil {
+		return nil, err
+	}
+	b := bufio.NewWriter(f)
+
+	mux := astits.NewMuxer(context.Background(), b)
+	mux.AddElementaryStream(astits.PMTElementaryStream{
+		ElementaryPID: 256,
+		StreamType:    astits.StreamTypeH264Video,
+	})
+	mux.SetPCRPID(256)
+
+	return &mpegtsMuxer{
+		sps: sps,
+		pps: pps,
+		f:   f,
+		b:   b,
+		mux: mux,
+	}, nil
+}
+
+// close closes all the mpegtsMuxer resources.
+func (e *mpegtsMuxer) close() {
+	e.b.Flush()
+	e.f.Close()
+}
+
+// encode encodes H264 NALUs into MPEG-TS.
+func (e *mpegtsMuxer) encode(nalus [][]byte, pts time.Duration) error {
+	// prepend an AUD. This is required by some players
+	filteredNALUs := [][]byte{
+		{byte(h264.NALUTypeAccessUnitDelimiter), 240},
+	}
+
+	nonIDRPresent := false
+	idrPresent := false
+
+	for _, nalu := range nalus {
+		typ := h264.NALUType(nalu[0] & 0x1F)
+		switch typ {
+		case h264.NALUTypeSPS:
+			e.sps = append([]byte(nil), nalu...)
+			continue
+
+		case h264.NALUTypePPS:
+			e.pps = append([]byte(nil), nalu...)
+			continue
+
+		case h264.NALUTypeAccessUnitDelimiter:
+			continue
+
+		case h264.NALUTypeIDR:
+			idrPresent = true
+
+		case h264.NALUTypeNonIDR:
+			nonIDRPresent = true
+		}
+
+		filteredNALUs = append(filteredNALUs, nalu)
+	}
+
+	nalus = filteredNALUs
+
+	if !nonIDRPresent && !idrPresent {
+		return nil
+	}
+
+	// add SPS and PPS before every group that contains an IDR
+	if idrPresent {
+		nalus = append([][]byte{e.sps, e.pps}, nalus...)
+	}
+
+	var dts time.Duration
+
+	if !e.firstIDRReceived {
+		// skip samples silently until we find one with a IDR
+		if !idrPresent {
+			return nil
+		}
+
+		e.firstIDRReceived = true
+		e.dtsExtractor = h264.NewDTSExtractor()
+
+		var err error
+		dts, err = e.dtsExtractor.Extract(nalus, pts)
+		if err != nil {
+			return err
+		}
+
+		e.startDTS = dts
+		dts = 0
+		pts -= e.startDTS
+
+	} else {
+		var err error
+		dts, err = e.dtsExtractor.Extract(nalus, pts)
+		if err != nil {
+			return err
+		}
+
+		dts -= e.startDTS
+		pts -= e.startDTS
+	}
+
+	oh := &astits.PESOptionalHeader{
+		MarkerBits: 2,
+	}
+
+	if dts == pts {
+		oh.PTSDTSIndicator = astits.PTSDTSIndicatorOnlyPTS
+		oh.PTS = &astits.ClockReference{Base: int64(pts.Seconds() * 90000)}
+	} else {
+		oh.PTSDTSIndicator = astits.PTSDTSIndicatorBothPresent
+		oh.DTS = &astits.ClockReference{Base: int64(dts.Seconds() * 90000)}
+		oh.PTS = &astits.ClockReference{Base: int64(pts.Seconds() * 90000)}
+	}
+
+	// encode into Annex-B
+	annexb, err := h264.AnnexBMarshal(nalus)
+	if err != nil {
+		return err
+	}
+
+	// write TS packet
+	_, err = e.mux.WriteData(&astits.MuxerData{
+		PID: 256,
+		AdaptationField: &astits.PacketAdaptationField{
+			RandomAccessIndicator: idrPresent,
+		},
+		PES: &astits.PESData{
+			Header: &astits.PESHeader{
+				OptionalHeader: oh,
+				StreamID:       224, // video
+			},
+			Data: annexb,
+		},
+	})
+	if err != nil {
+		return err
+	}
+
+	log.Println("wrote TS packet")
+	return nil
+}