Add H264 send/receive and packetization support

pkg/rtp/codecs/h264_packet.go

@@ -0,0 +1,123 @@
+package codecs
+
+// H264Payloader payloads H264 packets
+type H264Payloader struct{}
+
+const (
+	fuaHeaderSize = 2
+)
+
+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
+
+	emitNalus(payload, func(nalu []byte) {
+		naluType := nalu[0] & 0x1F
+		naluRefIdc := nalu[0] & 0x60
+
+		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
+
+		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] = 28
+			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
+}