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decoder.go
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decoder.go
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package rtpav1
import (
"errors"
"fmt"
"github.com/bluenviron/mediacommon/pkg/codecs/av1"
"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 NALU 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/AV1 decoder.
// Specification: https://aomediacodec.github.io/av1-rtp-spec/
type Decoder struct {
firstPacketReceived bool
fragmentsSize int
fragments [][]byte
// for Decode()
frameBuffer [][]byte
frameBufferLen int
frameBufferSize int
}
// Init initializes the decoder.
func (d *Decoder) Init() error {
return nil
}
func (d *Decoder) decodeOBUs(pkt *rtp.Packet) ([][]byte, error) {
var av1header codecs.AV1Packet
_, err := av1header.Unmarshal(pkt.Payload)
if err != nil {
d.fragments = d.fragments[:0] // discard pending fragments
d.fragmentsSize = 0
return nil, fmt.Errorf("invalid header: %v", err)
}
for _, el := range av1header.OBUElements {
if len(el) == 0 {
return nil, fmt.Errorf("invalid OBU fragment")
}
}
if av1header.Z {
if len(d.fragments) == 0 {
if !d.firstPacketReceived {
return nil, ErrNonStartingPacketAndNoPrevious
}
return nil, fmt.Errorf("received a subsequent fragment without previous fragments")
}
d.fragmentsSize += len(av1header.OBUElements[0])
if d.fragmentsSize > av1.MaxTemporalUnitSize {
d.fragments = d.fragments[:0]
d.fragmentsSize = 0
return nil, fmt.Errorf("OBU size (%d) is too big, maximum is %d", d.fragmentsSize, av1.MaxTemporalUnitSize)
}
d.fragments = append(d.fragments, av1header.OBUElements[0])
av1header.OBUElements = av1header.OBUElements[1:]
}
d.firstPacketReceived = true
var obus [][]byte
if len(av1header.OBUElements) > 0 {
if d.fragmentsSize != 0 {
obus = append(obus, joinFragments(d.fragments, d.fragmentsSize))
d.fragments = d.fragments[:0]
d.fragmentsSize = 0
}
if av1header.Y {
elementCount := len(av1header.OBUElements)
d.fragmentsSize += len(av1header.OBUElements[elementCount-1])
if d.fragmentsSize > av1.MaxTemporalUnitSize {
d.fragments = d.fragments[:0]
d.fragmentsSize = 0
return nil, fmt.Errorf("OBU size (%d) is too big, maximum is %d", d.fragmentsSize, av1.MaxTemporalUnitSize)
}
d.fragments = append(d.fragments, av1header.OBUElements[elementCount-1])
av1header.OBUElements = av1header.OBUElements[:elementCount-1]
}
obus = append(obus, av1header.OBUElements...)
} else if !av1header.Y {
obus = append(obus, joinFragments(d.fragments, d.fragmentsSize))
d.fragments = d.fragments[:0]
d.fragmentsSize = 0
}
if len(obus) == 0 {
return nil, ErrMorePacketsNeeded
}
return obus, nil
}
// Decode decodes a temporal unit from a RTP packet.
func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
obus, err := d.decodeOBUs(pkt)
if err != nil {
return nil, err
}
l := len(obus)
if (d.frameBufferLen + l) > av1.MaxOBUsPerTemporalUnit {
d.frameBuffer = nil
d.frameBufferLen = 0
d.frameBufferSize = 0
return nil, fmt.Errorf("OBU count exceeds maximum allowed (%d)",
av1.MaxOBUsPerTemporalUnit)
}
addSize := 0
for _, obu := range obus {
addSize += len(obu)
}
if (d.frameBufferSize + addSize) > av1.MaxTemporalUnitSize {
d.frameBuffer = nil
d.frameBufferLen = 0
d.frameBufferSize = 0
return nil, fmt.Errorf("temporal unit size (%d) is too big, maximum is %d",
d.frameBufferSize+addSize, av1.MaxOBUsPerTemporalUnit)
}
d.frameBuffer = append(d.frameBuffer, obus...)
d.frameBufferLen += l
d.frameBufferSize += addSize
if !pkt.Marker {
return nil, ErrMorePacketsNeeded
}
ret := d.frameBuffer
// do not reuse frameBuffer to avoid race conditions
d.frameBuffer = nil
d.frameBufferLen = 0
d.frameBufferSize = 0
return ret, nil
}