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decoder.go
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decoder.go
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package rtpvp9
import (
"errors"
"fmt"
"github.com/bluenviron/mediacommon/pkg/codecs/vp9"
"github.com/pion/rtp"
"github.com/pion/rtp/codecs"
)
// 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 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")
func joinFragments(fragments [][]byte, size int) []byte {
ret := make([]byte, size)
n := 0
for _, p := range fragments {
n += copy(ret[n:], p)
}
return ret
}
// Decoder is a RTP/VP9 decoder.
// Specification: https://datatracker.ietf.org/doc/html/draft-ietf-payload-vp9-16
type Decoder struct {
firstPacketReceived bool
fragmentsSize int
fragments [][]byte
}
// Init initializes the decoder.
func (d *Decoder) Init() error {
return nil
}
// Decode decodes a VP9 frame from a RTP packet.
func (d *Decoder) Decode(pkt *rtp.Packet) ([]byte, error) {
var vpkt codecs.VP9Packet
_, err := vpkt.Unmarshal(pkt.Payload)
if err != nil {
d.fragments = d.fragments[:0] // discard pending fragments
return nil, err
}
var frame []byte
if vpkt.B {
d.fragments = d.fragments[:0] // discard pending fragments
d.firstPacketReceived = true
if !vpkt.E {
d.fragmentsSize = len(vpkt.Payload)
d.fragments = append(d.fragments, vpkt.Payload)
return nil, ErrMorePacketsNeeded
}
frame = vpkt.Payload
} else {
if len(d.fragments) == 0 {
if !d.firstPacketReceived {
return nil, ErrNonStartingPacketAndNoPrevious
}
return nil, fmt.Errorf("received a non-starting fragment")
}
d.fragmentsSize += len(vpkt.Payload)
if d.fragmentsSize > vp9.MaxFrameSize {
d.fragments = d.fragments[:0] // discard pending fragments
return nil, fmt.Errorf("frame size (%d) is too big, maximum is %d", d.fragmentsSize, vp9.MaxFrameSize)
}
d.fragments = append(d.fragments, vpkt.Payload)
if !vpkt.E {
return nil, ErrMorePacketsNeeded
}
frame = joinFragments(d.fragments, d.fragmentsSize)
d.fragments = d.fragments[:0]
}
return frame, nil
}