284 lines
8.2 KiB
Go
284 lines
8.2 KiB
Go
package rtcp
|
|
|
|
import (
|
|
"bytes"
|
|
"encoding/binary"
|
|
"fmt"
|
|
"math"
|
|
)
|
|
|
|
// ReceiverEstimatedMaximumBitrate contains the receiver's estimated maximum bitrate.
|
|
// see: https://tools.ietf.org/html/draft-alvestrand-rmcat-remb-03
|
|
type ReceiverEstimatedMaximumBitrate struct {
|
|
// SSRC of sender
|
|
SenderSSRC uint32
|
|
|
|
// Estimated maximum bitrate
|
|
Bitrate float32
|
|
|
|
// SSRC entries which this packet applies to
|
|
SSRCs []uint32
|
|
}
|
|
|
|
// Marshal serializes the packet and returns a byte slice.
|
|
func (p ReceiverEstimatedMaximumBitrate) Marshal() (buf []byte, err error) {
|
|
// Allocate a buffer of the exact output size.
|
|
buf = make([]byte, p.MarshalSize())
|
|
|
|
// Write to our buffer.
|
|
n, err := p.MarshalTo(buf)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
// This will always be true but just to be safe.
|
|
if n != len(buf) {
|
|
return nil, errWrongMarshalSize
|
|
}
|
|
|
|
return buf, nil
|
|
}
|
|
|
|
// MarshalSize returns the size of the packet when marshaled.
|
|
// This can be used in conjunction with `MarshalTo` to avoid allocations.
|
|
func (p ReceiverEstimatedMaximumBitrate) MarshalSize() (n int) {
|
|
return 20 + 4*len(p.SSRCs)
|
|
}
|
|
|
|
// MarshalTo serializes the packet to the given byte slice.
|
|
func (p ReceiverEstimatedMaximumBitrate) MarshalTo(buf []byte) (n int, err error) {
|
|
const bitratemax = 0x3FFFFp+63
|
|
/*
|
|
0 1 2 3
|
|
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
|V=2|P| FMT=15 | PT=206 | length |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| SSRC of packet sender |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| SSRC of media source |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| Unique identifier 'R' 'E' 'M' 'B' |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| Num SSRC | BR Exp | BR Mantissa |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| SSRC feedback |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| ... |
|
|
*/
|
|
|
|
size := p.MarshalSize()
|
|
if len(buf) < size {
|
|
return 0, errPacketTooShort
|
|
}
|
|
|
|
buf[0] = 143 // v=2, p=0, fmt=15
|
|
buf[1] = 206
|
|
|
|
// Length of this packet in 32-bit words minus one.
|
|
length := uint16((p.MarshalSize() / 4) - 1)
|
|
binary.BigEndian.PutUint16(buf[2:4], length)
|
|
|
|
binary.BigEndian.PutUint32(buf[4:8], p.SenderSSRC)
|
|
binary.BigEndian.PutUint32(buf[8:12], 0) // always zero
|
|
|
|
// ALL HAIL REMB
|
|
buf[12] = 'R'
|
|
buf[13] = 'E'
|
|
buf[14] = 'M'
|
|
buf[15] = 'B'
|
|
|
|
// Write the length of the ssrcs to follow at the end
|
|
buf[16] = byte(len(p.SSRCs))
|
|
|
|
exp := 0
|
|
bitrate := p.Bitrate
|
|
|
|
if bitrate >= bitratemax {
|
|
bitrate = bitratemax
|
|
}
|
|
|
|
if bitrate < 0 {
|
|
return 0, errInvalidBitrate
|
|
}
|
|
|
|
for bitrate >= (1 << 18) {
|
|
bitrate /= 2.0
|
|
exp++
|
|
}
|
|
|
|
if exp >= (1 << 6) {
|
|
return 0, errInvalidBitrate
|
|
}
|
|
|
|
mantissa := uint(math.Floor(float64(bitrate)))
|
|
|
|
// We can't quite use the binary package because
|
|
// a) it's a uint24 and b) the exponent is only 6-bits
|
|
// Just trust me; this is big-endian encoding.
|
|
buf[17] = byte(exp<<2) | byte(mantissa>>16)
|
|
buf[18] = byte(mantissa >> 8)
|
|
buf[19] = byte(mantissa)
|
|
|
|
// Write the SSRCs at the very end.
|
|
n = 20
|
|
for _, ssrc := range p.SSRCs {
|
|
binary.BigEndian.PutUint32(buf[n:n+4], ssrc)
|
|
n += 4
|
|
}
|
|
|
|
return n, nil
|
|
}
|
|
|
|
// Unmarshal reads a REMB packet from the given byte slice.
|
|
func (p *ReceiverEstimatedMaximumBitrate) Unmarshal(buf []byte) (err error) {
|
|
const mantissamax = 0x7FFFFF
|
|
/*
|
|
0 1 2 3
|
|
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
|V=2|P| FMT=15 | PT=206 | length |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| SSRC of packet sender |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| SSRC of media source |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| Unique identifier 'R' 'E' 'M' 'B' |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| Num SSRC | BR Exp | BR Mantissa |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| SSRC feedback |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| ... |
|
|
*/
|
|
|
|
// 20 bytes is the size of the packet with no SSRCs
|
|
if len(buf) < 20 {
|
|
return errPacketTooShort
|
|
}
|
|
|
|
// version must be 2
|
|
version := buf[0] >> 6
|
|
if version != 2 {
|
|
return fmt.Errorf("%w expected(2) actual(%d)", errBadVersion, version)
|
|
}
|
|
|
|
// padding must be unset
|
|
padding := (buf[0] >> 5) & 1
|
|
if padding != 0 {
|
|
return fmt.Errorf("%w expected(0) actual(%d)", errWrongPadding, padding)
|
|
}
|
|
|
|
// fmt must be 15
|
|
fmtVal := buf[0] & 31
|
|
if fmtVal != 15 {
|
|
return fmt.Errorf("%w expected(15) actual(%d)", errWrongFeedbackType, fmtVal)
|
|
}
|
|
|
|
// Must be payload specific feedback
|
|
if buf[1] != 206 {
|
|
return fmt.Errorf("%w expected(206) actual(%d)", errWrongPayloadType, buf[1])
|
|
}
|
|
|
|
// length is the number of 32-bit words, minus 1
|
|
length := binary.BigEndian.Uint16(buf[2:4])
|
|
size := int((length + 1) * 4)
|
|
|
|
// There's not way this could be legit
|
|
if size < 20 {
|
|
return errHeaderTooSmall
|
|
}
|
|
|
|
// Make sure the buffer is large enough.
|
|
if len(buf) < size {
|
|
return errPacketTooShort
|
|
}
|
|
|
|
// The sender SSRC is 32-bits
|
|
p.SenderSSRC = binary.BigEndian.Uint32(buf[4:8])
|
|
|
|
// The destination SSRC must be 0
|
|
media := binary.BigEndian.Uint32(buf[8:12])
|
|
if media != 0 {
|
|
return errSSRCMustBeZero
|
|
}
|
|
|
|
// REMB rules all around me
|
|
if !bytes.Equal(buf[12:16], []byte{'R', 'E', 'M', 'B'}) {
|
|
return errMissingREMBidentifier
|
|
}
|
|
|
|
// The next byte is the number of SSRC entries at the end.
|
|
num := int(buf[16])
|
|
|
|
// Now we know the expected size, make sure they match.
|
|
if size != 20+4*num {
|
|
return errSSRCNumAndLengthMismatch
|
|
}
|
|
|
|
// Get the 6-bit exponent value.
|
|
exp := buf[17] >> 2
|
|
exp += 127 // bias for IEEE754
|
|
exp += 23 // IEEE754 biases the decimal to the left, abs-send-time biases it to the right
|
|
|
|
// The remaining 2-bits plus the next 16-bits are the mantissa.
|
|
mantissa := uint32(buf[17]&3)<<16 | uint32(buf[18])<<8 | uint32(buf[19])
|
|
|
|
if mantissa != 0 {
|
|
// ieee754 requires an implicit leading bit
|
|
for (mantissa & (mantissamax + 1)) == 0 {
|
|
exp--
|
|
mantissa *= 2
|
|
}
|
|
}
|
|
|
|
// bitrate = mantissa * 2^exp
|
|
p.Bitrate = math.Float32frombits((uint32(exp) << 23) | (mantissa & mantissamax))
|
|
|
|
// Clear any existing SSRCs
|
|
p.SSRCs = nil
|
|
|
|
// Loop over and parse the SSRC entires at the end.
|
|
// We already verified that size == num * 4
|
|
for n := 20; n < size; n += 4 {
|
|
ssrc := binary.BigEndian.Uint32(buf[n : n+4])
|
|
p.SSRCs = append(p.SSRCs, ssrc)
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// Header returns the Header associated with this packet.
|
|
func (p *ReceiverEstimatedMaximumBitrate) Header() Header {
|
|
return Header{
|
|
Count: FormatREMB,
|
|
Type: TypePayloadSpecificFeedback,
|
|
Length: uint16((p.MarshalSize() / 4) - 1),
|
|
}
|
|
}
|
|
|
|
// String prints the REMB packet in a human-readable format.
|
|
func (p *ReceiverEstimatedMaximumBitrate) String() string {
|
|
// Keep a table of powers to units for fast conversion.
|
|
bitUnits := []string{"b", "Kb", "Mb", "Gb", "Tb", "Pb", "Eb"}
|
|
|
|
// Do some unit conversions because b/s is far too difficult to read.
|
|
bitrate := p.Bitrate
|
|
powers := 0
|
|
|
|
// Keep dividing the bitrate until it's under 1000
|
|
for bitrate >= 1000.0 && powers < len(bitUnits) {
|
|
bitrate /= 1000.0
|
|
powers++
|
|
}
|
|
|
|
unit := bitUnits[powers]
|
|
|
|
return fmt.Sprintf("ReceiverEstimatedMaximumBitrate %x %.2f %s/s", p.SenderSSRC, bitrate, unit)
|
|
}
|
|
|
|
// DestinationSSRC returns an array of SSRC values that this packet refers to.
|
|
func (p *ReceiverEstimatedMaximumBitrate) DestinationSSRC() []uint32 {
|
|
return p.SSRCs
|
|
}
|