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package rtcp
import "encoding/binary"
// A ReceptionReport block conveys statistics on the reception of RTP packets
// from a single synchronization source.
type ReceptionReport struct {
// The SSRC identifier of the source to which the information in this
// reception report block pertains.
SSRC uint32
// The fraction of RTP data packets from source SSRC lost since the
// previous SR or RR packet was sent, expressed as a fixed point
// number with the binary point at the left edge of the field.
FractionLost uint8
// The total number of RTP data packets from source SSRC that have
// been lost since the beginning of reception.
TotalLost uint32
// The low 16 bits contain the highest sequence number received in an
// RTP data packet from source SSRC, and the most significant 16
// bits extend that sequence number with the corresponding count of
// sequence number cycles.
LastSequenceNumber uint32
// An estimate of the statistical variance of the RTP data packet
// interarrival time, measured in timestamp units and expressed as an
// unsigned integer.
Jitter uint32
// The middle 32 bits out of 64 in the NTP timestamp received as part of
// the most recent RTCP sender report (SR) packet from source SSRC. If no
// SR has been received yet, the field is set to zero.
LastSenderReport uint32
// The delay, expressed in units of 1/65536 seconds, between receiving the
// last SR packet from source SSRC and sending this reception report block.
// If no SR packet has been received yet from SSRC, the field is set to zero.
Delay uint32
}
const (
receptionReportLength = 24
fractionLostOffset = 4
totalLostOffset = 5
lastSeqOffset = 8
jitterOffset = 12
lastSROffset = 16
delayOffset = 20
)
// Marshal encodes the ReceptionReport in binary
func (r ReceptionReport) Marshal() ([]byte, error) {
/*
* 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
* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
* | SSRC |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | fraction lost | cumulative number of packets lost |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | extended highest sequence number received |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | interarrival jitter |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | last SR (LSR) |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | delay since last SR (DLSR) |
* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
*/
rawPacket := make([]byte, receptionReportLength)
binary.BigEndian.PutUint32(rawPacket, r.SSRC)
rawPacket[fractionLostOffset] = r.FractionLost
// pack TotalLost into 24 bits
if r.TotalLost >= (1 << 25) {
return nil, errInvalidTotalLost
}
tlBytes := rawPacket[totalLostOffset:]
tlBytes[0] = byte(r.TotalLost >> 16)
tlBytes[1] = byte(r.TotalLost >> 8)
tlBytes[2] = byte(r.TotalLost)
binary.BigEndian.PutUint32(rawPacket[lastSeqOffset:], r.LastSequenceNumber)
binary.BigEndian.PutUint32(rawPacket[jitterOffset:], r.Jitter)
binary.BigEndian.PutUint32(rawPacket[lastSROffset:], r.LastSenderReport)
binary.BigEndian.PutUint32(rawPacket[delayOffset:], r.Delay)
return rawPacket, nil
}
// Unmarshal decodes the ReceptionReport from binary
func (r *ReceptionReport) Unmarshal(rawPacket []byte) error {
if len(rawPacket) < receptionReportLength {
return errPacketTooShort
}
/*
* 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
* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
* | SSRC |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | fraction lost | cumulative number of packets lost |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | extended highest sequence number received |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | interarrival jitter |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | last SR (LSR) |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | delay since last SR (DLSR) |
* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
*/
r.SSRC = binary.BigEndian.Uint32(rawPacket)
r.FractionLost = rawPacket[fractionLostOffset]
tlBytes := rawPacket[totalLostOffset:]
r.TotalLost = uint32(tlBytes[2]) | uint32(tlBytes[1])<<8 | uint32(tlBytes[0])<<16
r.LastSequenceNumber = binary.BigEndian.Uint32(rawPacket[lastSeqOffset:])
r.Jitter = binary.BigEndian.Uint32(rawPacket[jitterOffset:])
r.LastSenderReport = binary.BigEndian.Uint32(rawPacket[lastSROffset:])
r.Delay = binary.BigEndian.Uint32(rawPacket[delayOffset:])
return nil
}
func (r *ReceptionReport) len() int {
return receptionReportLength
}
|
