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|
package codecs
import (
"encoding/binary"
"fmt"
)
// H264Payloader payloads H264 packets
type H264Payloader struct{}
const (
stapaNALUType = 24
fuaNALUType = 28
fuaHeaderSize = 2
stapaHeaderSize = 1
stapaNALULengthSize = 2
naluTypeBitmask = 0x1F
naluRefIdcBitmask = 0x60
fuaStartBitmask = 0x80
)
func annexbNALUStartCode() []byte { return []byte{0x00, 0x00, 0x00, 0x01} }
func emitNalus(nals []byte, emit func([]byte)) {
nextInd := func(nalu []byte, start int) (indStart int, indLen int) {
zeroCount := 0
for i, b := range nalu[start:] {
if b == 0 {
zeroCount++
continue
} else if b == 1 {
if zeroCount >= 2 {
return start + i - zeroCount, zeroCount + 1
}
}
zeroCount = 0
}
return -1, -1
}
nextIndStart, nextIndLen := nextInd(nals, 0)
if nextIndStart == -1 {
emit(nals)
} else {
for nextIndStart != -1 {
prevStart := nextIndStart + nextIndLen
nextIndStart, nextIndLen = nextInd(nals, prevStart)
if nextIndStart != -1 {
emit(nals[prevStart:nextIndStart])
} else {
// Emit until end of stream, no end indicator found
emit(nals[prevStart:])
}
}
}
}
// Payload fragments a H264 packet across one or more byte arrays
func (p *H264Payloader) Payload(mtu int, payload []byte) [][]byte {
var payloads [][]byte
if len(payload) == 0 {
return payloads
}
emitNalus(payload, func(nalu []byte) {
if len(nalu) == 0 {
return
}
naluType := nalu[0] & naluTypeBitmask
naluRefIdc := nalu[0] & naluRefIdcBitmask
if naluType == 9 || naluType == 12 {
return
}
// Single NALU
if len(nalu) <= mtu {
out := make([]byte, len(nalu))
copy(out, nalu)
payloads = append(payloads, out)
return
}
// FU-A
maxFragmentSize := mtu - fuaHeaderSize
// The FU payload consists of fragments of the payload of the fragmented
// NAL unit so that if the fragmentation unit payloads of consecutive
// FUs are sequentially concatenated, the payload of the fragmented NAL
// unit can be reconstructed. The NAL unit type octet of the fragmented
// NAL unit is not included as such in the fragmentation unit payload,
// but rather the information of the NAL unit type octet of the
// fragmented NAL unit is conveyed in the F and NRI fields of the FU
// indicator octet of the fragmentation unit and in the type field of
// the FU header. An FU payload MAY have any number of octets and MAY
// be empty.
naluData := nalu
// According to the RFC, the first octet is skipped due to redundant information
naluDataIndex := 1
naluDataLength := len(nalu) - naluDataIndex
naluDataRemaining := naluDataLength
if min(maxFragmentSize, naluDataRemaining) <= 0 {
return
}
for naluDataRemaining > 0 {
currentFragmentSize := min(maxFragmentSize, naluDataRemaining)
out := make([]byte, fuaHeaderSize+currentFragmentSize)
// +---------------+
// |0|1|2|3|4|5|6|7|
// +-+-+-+-+-+-+-+-+
// |F|NRI| Type |
// +---------------+
out[0] = fuaNALUType
out[0] |= naluRefIdc
// +---------------+
// |0|1|2|3|4|5|6|7|
// +-+-+-+-+-+-+-+-+
// |S|E|R| Type |
// +---------------+
out[1] = naluType
if naluDataRemaining == naluDataLength {
// Set start bit
out[1] |= 1 << 7
} else if naluDataRemaining-currentFragmentSize == 0 {
// Set end bit
out[1] |= 1 << 6
}
copy(out[fuaHeaderSize:], naluData[naluDataIndex:naluDataIndex+currentFragmentSize])
payloads = append(payloads, out)
naluDataRemaining -= currentFragmentSize
naluDataIndex += currentFragmentSize
}
})
return payloads
}
// H264Packet represents the H264 header that is stored in the payload of an RTP Packet
type H264Packet struct {
}
// Unmarshal parses the passed byte slice and stores the result in the H264Packet this method is called upon
func (p *H264Packet) Unmarshal(payload []byte) ([]byte, error) {
if payload == nil {
return nil, errNilPacket
} else if len(payload) <= 2 {
return nil, fmt.Errorf("%w: %d <= 2", errShortPacket, len(payload))
}
// NALU Types
// https://tools.ietf.org/html/rfc6184#section-5.4
naluType := payload[0] & naluTypeBitmask
switch {
case naluType > 0 && naluType < 24:
return append(annexbNALUStartCode(), payload...), nil
case naluType == stapaNALUType:
currOffset := int(stapaHeaderSize)
result := []byte{}
for currOffset < len(payload) {
naluSize := int(binary.BigEndian.Uint16(payload[currOffset:]))
currOffset += stapaNALULengthSize
if len(payload) < currOffset+naluSize {
return nil, fmt.Errorf("%w STAP-A declared size(%d) is larger than buffer(%d)", errShortPacket, naluSize, len(payload)-currOffset)
}
result = append(result, annexbNALUStartCode()...)
result = append(result, payload[currOffset:currOffset+naluSize]...)
currOffset += naluSize
}
return result, nil
case naluType == fuaNALUType:
if len(payload) < fuaHeaderSize {
return nil, errShortPacket
}
if payload[1]&fuaStartBitmask != 0 {
naluRefIdc := payload[0] & naluRefIdcBitmask
fragmentedNaluType := payload[1] & naluTypeBitmask
// Take a copy of payload since we are mutating it.
payloadCopy := append([]byte{}, payload...)
payloadCopy[fuaHeaderSize-1] = naluRefIdc | fragmentedNaluType
return append(annexbNALUStartCode(), payloadCopy[fuaHeaderSize-1:]...), nil
}
return payload[fuaHeaderSize:], nil
}
return nil, fmt.Errorf("%w: %d", errUnhandledNALUType, naluType)
}
|
