support AC-3 tracks in SRT and UDP; support recording AC-3 tracks (#2376)

internal/formatprocessor/ac3.go

@@ -0,0 +1,112 @@
+package formatprocessor
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/bluenviron/gortsplib/v4/pkg/format"
+	"github.com/bluenviron/gortsplib/v4/pkg/format/rtpac3"
+	"github.com/pion/rtp"
+
+	"github.com/bluenviron/mediamtx/internal/unit"
+)
+
+type formatProcessorAC3 struct {
+	udpMaxPayloadSize int
+	format            *format.AC3
+	encoder           *rtpac3.Encoder
+	decoder           *rtpac3.Decoder
+}
+
+func newAC3(
+	udpMaxPayloadSize int,
+	forma *format.AC3,
+	generateRTPPackets bool,
+) (*formatProcessorAC3, error) {
+	t := &formatProcessorAC3{
+		udpMaxPayloadSize: udpMaxPayloadSize,
+		format:            forma,
+	}
+
+	if generateRTPPackets {
+		err := t.createEncoder()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return t, nil
+}
+
+func (t *formatProcessorAC3) createEncoder() error {
+	t.encoder = &rtpac3.Encoder{
+		PayloadType: t.format.PayloadTyp,
+	}
+	return t.encoder.Init()
+}
+
+func (t *formatProcessorAC3) ProcessUnit(uu unit.Unit) error { //nolint:dupl
+	u := uu.(*unit.AC3)
+
+	pkts, err := t.encoder.Encode(u.Frames)
+	if err != nil {
+		return err
+	}
+
+	ts := uint32(multiplyAndDivide(u.PTS, time.Duration(t.format.ClockRate()), time.Second))
+	for _, pkt := range pkts {
+		pkt.Timestamp = ts
+	}
+
+	u.RTPPackets = pkts
+
+	return nil
+}
+
+func (t *formatProcessorAC3) ProcessRTPPacket( //nolint:dupl
+	pkt *rtp.Packet,
+	ntp time.Time,
+	pts time.Duration,
+	hasNonRTSPReaders bool,
+) (Unit, error) {
+	u := &unit.AC3{
+		Base: unit.Base{
+			RTPPackets: []*rtp.Packet{pkt},
+			NTP:        ntp,
+			PTS:        pts,
+		},
+	}
+
+	// remove padding
+	pkt.Header.Padding = false
+	pkt.PaddingSize = 0
+
+	if pkt.MarshalSize() > t.udpMaxPayloadSize {
+		return nil, fmt.Errorf("payload size (%d) is greater than maximum allowed (%d)",
+			pkt.MarshalSize(), t.udpMaxPayloadSize)
+	}
+
+	// decode from RTP
+	if hasNonRTSPReaders || t.decoder != nil {
+		if t.decoder == nil {
+			var err error
+			t.decoder, err = t.format.CreateDecoder()
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		frames, err := t.decoder.Decode(pkt)
+		if err != nil {
+			if err == rtpac3.ErrNonStartingPacketAndNoPrevious || err == rtpac3.ErrMorePacketsNeeded {
+				return u, nil
+			}
+			return nil, err
+		}
+
+		u.Frames = frames
+	}
+
+	// route packet as is
+	return u, nil
+}

internal/formatprocessor/processor.go

@@ -72,6 +72,9 @@ func New(
 	case *format.MPEG1Audio:
 		return newMPEG1Audio(udpMaxPayloadSize, forma, generateRTPPackets)
 
+	case *format.AC3:
+		return newAC3(udpMaxPayloadSize, forma, generateRTPPackets)
+
 	default:
 		return newGeneric(udpMaxPayloadSize, forma, generateRTPPackets)
 	}