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package codecs
// VP8Payloader payloads VP8 packets
type VP8Payloader struct{}
const (
vp8HeaderSize = 1
)
// Payload fragments a VP8 packet across one or more byte arrays
func (p *VP8Payloader) Payload(mtu int, payload []byte) [][]byte {
/*
* https://tools.ietf.org/html/rfc7741#section-4.2
*
* 0 1 2 3 4 5 6 7
* +-+-+-+-+-+-+-+-+
* |X|R|N|S|R| PID | (REQUIRED)
* +-+-+-+-+-+-+-+-+
* X: |I|L|T|K| RSV | (OPTIONAL)
* +-+-+-+-+-+-+-+-+
* I: |M| PictureID | (OPTIONAL)
* +-+-+-+-+-+-+-+-+
* L: | TL0PICIDX | (OPTIONAL)
* +-+-+-+-+-+-+-+-+
* T/K: |TID|Y| KEYIDX | (OPTIONAL)
* +-+-+-+-+-+-+-+-+
* S: Start of VP8 partition. SHOULD be set to 1 when the first payload
* octet of the RTP packet is the beginning of a new VP8 partition,
* and MUST NOT be 1 otherwise. The S bit MUST be set to 1 for the
* first packet of each encoded frame.
*/
maxFragmentSize := mtu - vp8HeaderSize
payloadData := payload
payloadDataRemaining := len(payload)
payloadDataIndex := 0
var payloads [][]byte
// Make sure the fragment/payload size is correct
if min(maxFragmentSize, payloadDataRemaining) <= 0 {
return payloads
}
for payloadDataRemaining > 0 {
currentFragmentSize := min(maxFragmentSize, payloadDataRemaining)
out := make([]byte, vp8HeaderSize+currentFragmentSize)
if payloadDataRemaining == len(payload) {
out[0] = 0x10
}
copy(out[vp8HeaderSize:], payloadData[payloadDataIndex:payloadDataIndex+currentFragmentSize])
payloads = append(payloads, out)
payloadDataRemaining -= currentFragmentSize
payloadDataIndex += currentFragmentSize
}
return payloads
}
// VP8Packet represents the VP8 header that is stored in the payload of an RTP Packet
type VP8Packet struct {
// Required Header
X uint8 /* extended controlbits present */
N uint8 /* (non-reference frame) when set to 1 this frame can be discarded */
S uint8 /* start of VP8 partition */
PID uint8 /* partition index */
// Optional Header
I uint8 /* 1 if PictureID is present */
L uint8 /* 1 if TL0PICIDX is present */
T uint8 /* 1 if TID is present */
K uint8 /* 1 if KEYIDX is present */
PictureID uint16 /* 8 or 16 bits, picture ID */
TL0PICIDX uint8 /* 8 bits temporal level zero index */
Payload []byte
}
// Unmarshal parses the passed byte slice and stores the result in the VP8Packet this method is called upon
func (p *VP8Packet) Unmarshal(payload []byte) ([]byte, error) {
if payload == nil {
return nil, errNilPacket
}
payloadLen := len(payload)
if payloadLen < 4 {
return nil, errShortPacket
}
payloadIndex := 0
p.X = (payload[payloadIndex] & 0x80) >> 7
p.N = (payload[payloadIndex] & 0x20) >> 5
p.S = (payload[payloadIndex] & 0x10) >> 4
p.PID = payload[payloadIndex] & 0x07
payloadIndex++
if p.X == 1 {
p.I = (payload[payloadIndex] & 0x80) >> 7
p.L = (payload[payloadIndex] & 0x40) >> 6
p.T = (payload[payloadIndex] & 0x20) >> 5
p.K = (payload[payloadIndex] & 0x10) >> 4
payloadIndex++
}
if p.I == 1 { // PID present?
if payload[payloadIndex]&0x80 > 0 { // M == 1, PID is 16bit
payloadIndex += 2
} else {
payloadIndex++
}
}
if p.L == 1 {
payloadIndex++
}
if p.T == 1 || p.K == 1 {
payloadIndex++
}
if payloadIndex >= payloadLen {
return nil, errShortPacket
}
p.Payload = payload[payloadIndex:]
return p.Payload, nil
}
// VP8PartitionHeadChecker checks VP8 partition head
type VP8PartitionHeadChecker struct{}
// IsPartitionHead checks whether if this is a head of the VP8 partition
func (*VP8PartitionHeadChecker) IsPartitionHead(packet []byte) bool {
p := &VP8Packet{}
if _, err := p.Unmarshal(packet); err != nil {
return false
}
return p.S == 1
}
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