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124 lines
3.1 KiB
Go
124 lines
3.1 KiB
Go
package codecs
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// H264Payloader payloads H264 packets
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type H264Payloader struct{}
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const (
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fuaHeaderSize = 2
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)
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func emitNalus(nals []byte, emit func([]byte)) {
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nextInd := func(nalu []byte, start int) (indStart int, indLen int) {
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zeroCount := 0
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for i, b := range nalu[start:] {
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if b == 0 {
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zeroCount++
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continue
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} else if b == 1 {
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if zeroCount >= 2 {
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return start + i - zeroCount, zeroCount + 1
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}
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}
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zeroCount = 0
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}
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return -1, -1
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}
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nextIndStart, nextIndLen := nextInd(nals, 0)
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if nextIndStart == -1 {
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emit(nals)
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} else {
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for nextIndStart != -1 {
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prevStart := nextIndStart + nextIndLen
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nextIndStart, nextIndLen = nextInd(nals, prevStart)
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if nextIndStart != -1 {
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emit(nals[prevStart:nextIndStart])
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} else {
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// Emit until end of stream, no end indicator found
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emit(nals[prevStart:])
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}
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}
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}
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}
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// Payload fragments a H264 packet across one or more byte arrays
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func (p *H264Payloader) Payload(mtu int, payload []byte) [][]byte {
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var payloads [][]byte
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emitNalus(payload, func(nalu []byte) {
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naluType := nalu[0] & 0x1F
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naluRefIdc := nalu[0] & 0x60
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if naluType == 9 || naluType == 12 {
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return
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}
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// Single NALU
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if len(nalu) <= mtu {
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out := make([]byte, len(nalu))
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copy(out, nalu)
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payloads = append(payloads, out)
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return
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}
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// FU-A
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maxFragmentSize := mtu - fuaHeaderSize
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// The FU payload consists of fragments of the payload of the fragmented
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// NAL unit so that if the fragmentation unit payloads of consecutive
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// FUs are sequentially concatenated, the payload of the fragmented NAL
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// unit can be reconstructed. The NAL unit type octet of the fragmented
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// NAL unit is not included as such in the fragmentation unit payload,
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// but rather the information of the NAL unit type octet of the
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// fragmented NAL unit is conveyed in the F and NRI fields of the FU
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// indicator octet of the fragmentation unit and in the type field of
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// the FU header. An FU payload MAY have any number of octets and MAY
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// be empty.
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naluData := nalu
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// According to the RFC, the first octet is skipped due to redundant information
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naluDataIndex := 1
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naluDataLength := len(nalu) - naluDataIndex
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naluDataRemaining := naluDataLength
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for naluDataRemaining > 0 {
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currentFragmentSize := min(maxFragmentSize, naluDataRemaining)
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out := make([]byte, fuaHeaderSize+currentFragmentSize)
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// +---------------+
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// |0|1|2|3|4|5|6|7|
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// +-+-+-+-+-+-+-+-+
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// |F|NRI| Type |
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// +---------------+
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out[0] = 28
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out[0] |= naluRefIdc
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// +---------------+
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//|0|1|2|3|4|5|6|7|
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//+-+-+-+-+-+-+-+-+
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//|S|E|R| Type |
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//+---------------+
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out[1] = naluType
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if naluDataRemaining == naluDataLength {
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// Set start bit
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out[1] |= 1 << 7
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} else if naluDataRemaining-currentFragmentSize == 0 {
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// Set end bit
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out[1] |= 1 << 6
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}
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copy(out[fuaHeaderSize:], naluData[naluDataIndex:naluDataIndex+currentFragmentSize])
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payloads = append(payloads, out)
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naluDataRemaining -= currentFragmentSize
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naluDataIndex += currentFragmentSize
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}
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})
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return payloads
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}
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