merge format and formatdecenc into formats (#222)

pkg/formats/rtpvp9/decoder.go

@@ -0,0 +1,88 @@
+package rtpvp9
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/pion/rtp"
+	"github.com/pion/rtp/codecs"
+
+	"github.com/bluenviron/gortsplib/v3/pkg/rtptime"
+)
+
+// ErrMorePacketsNeeded is returned when more packets are needed.
+var ErrMorePacketsNeeded = errors.New("need more packets")
+
+// ErrNonStartingPacketAndNoPrevious is returned when we received a non-starting
+// packet of a fragmented frame and we didn't received anything before.
+// It's normal to receive this when we are decoding a stream that has been already
+// running for some time.
+var ErrNonStartingPacketAndNoPrevious = errors.New(
+	"received a non-starting fragment without any previous starting fragment")
+
+// Decoder is a RTP/VP9 decoder.
+type Decoder struct {
+	timeDecoder         *rtptime.Decoder
+	firstPacketReceived bool
+	fragments           [][]byte
+}
+
+// Init initializes the decoder.
+func (d *Decoder) Init() {
+	d.timeDecoder = rtptime.NewDecoder(rtpClockRate)
+}
+
+// Decode decodes a VP9 frame from a RTP/VP9 packet.
+func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, time.Duration, error) {
+	var vpkt codecs.VP9Packet
+	_, err := vpkt.Unmarshal(pkt.Payload)
+	if err != nil {
+		d.fragments = d.fragments[:0] // discard pending fragmented packets
+		return nil, 0, err
+	}
+
+	var frame []byte
+
+	if vpkt.B {
+		d.fragments = d.fragments[:0] // discard pending fragmented packets
+		d.firstPacketReceived = true
+
+		if !vpkt.E {
+			d.fragments = append(d.fragments, vpkt.Payload)
+			return nil, 0, ErrMorePacketsNeeded
+		}
+
+		frame = vpkt.Payload
+	} else {
+		if len(d.fragments) == 0 {
+			if !d.firstPacketReceived {
+				return nil, 0, ErrNonStartingPacketAndNoPrevious
+			}
+
+			return nil, 0, fmt.Errorf("received a non-starting fragment")
+		}
+
+		d.fragments = append(d.fragments, vpkt.Payload)
+
+		if !vpkt.E {
+			return nil, 0, ErrMorePacketsNeeded
+		}
+
+		n := 0
+		for _, frag := range d.fragments {
+			n += len(frag)
+		}
+
+		frame = make([]byte, n)
+		pos := 0
+
+		for _, frag := range d.fragments {
+			pos += copy(frame[pos:], frag)
+		}
+
+		d.fragments = d.fragments[:0]
+	}
+
+	return frame, d.timeDecoder.Decode(pkt.Timestamp), nil
+}