131 lines
5.3 KiB
Go
131 lines
5.3 KiB
Go
package rtcp
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import "encoding/binary"
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// A ReceptionReport block conveys statistics on the reception of RTP packets
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// from a single synchronization source.
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type ReceptionReport struct {
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// The SSRC identifier of the source to which the information in this
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// reception report block pertains.
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SSRC uint32
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// The fraction of RTP data packets from source SSRC lost since the
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// previous SR or RR packet was sent, expressed as a fixed point
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// number with the binary point at the left edge of the field.
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FractionLost uint8
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// The total number of RTP data packets from source SSRC that have
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// been lost since the beginning of reception.
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TotalLost uint32
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// The low 16 bits contain the highest sequence number received in an
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// RTP data packet from source SSRC, and the most significant 16
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// bits extend that sequence number with the corresponding count of
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// sequence number cycles.
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LastSequenceNumber uint32
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// An estimate of the statistical variance of the RTP data packet
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// interarrival time, measured in timestamp units and expressed as an
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// unsigned integer.
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Jitter uint32
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// The middle 32 bits out of 64 in the NTP timestamp received as part of
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// the most recent RTCP sender report (SR) packet from source SSRC. If no
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// SR has been received yet, the field is set to zero.
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LastSenderReport uint32
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// The delay, expressed in units of 1/65536 seconds, between receiving the
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// last SR packet from source SSRC and sending this reception report block.
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// If no SR packet has been received yet from SSRC, the field is set to zero.
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Delay uint32
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}
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const (
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receptionReportLength = 24
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fractionLostOffset = 4
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totalLostOffset = 5
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lastSeqOffset = 8
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jitterOffset = 12
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lastSROffset = 16
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delayOffset = 20
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)
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// Marshal encodes the ReceptionReport in binary
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func (r ReceptionReport) Marshal() ([]byte, error) {
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/*
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* 0 1 2 3
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* 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
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* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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* | SSRC |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | fraction lost | cumulative number of packets lost |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | extended highest sequence number received |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | interarrival jitter |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | last SR (LSR) |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | delay since last SR (DLSR) |
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* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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*/
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rawPacket := make([]byte, receptionReportLength)
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binary.BigEndian.PutUint32(rawPacket, r.SSRC)
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rawPacket[fractionLostOffset] = r.FractionLost
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// pack TotalLost into 24 bits
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if r.TotalLost >= (1 << 25) {
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return nil, errInvalidTotalLost
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}
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tlBytes := rawPacket[totalLostOffset:]
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tlBytes[0] = byte(r.TotalLost >> 16)
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tlBytes[1] = byte(r.TotalLost >> 8)
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tlBytes[2] = byte(r.TotalLost)
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binary.BigEndian.PutUint32(rawPacket[lastSeqOffset:], r.LastSequenceNumber)
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binary.BigEndian.PutUint32(rawPacket[jitterOffset:], r.Jitter)
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binary.BigEndian.PutUint32(rawPacket[lastSROffset:], r.LastSenderReport)
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binary.BigEndian.PutUint32(rawPacket[delayOffset:], r.Delay)
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return rawPacket, nil
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}
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// Unmarshal decodes the ReceptionReport from binary
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func (r *ReceptionReport) Unmarshal(rawPacket []byte) error {
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if len(rawPacket) < receptionReportLength {
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return errPacketTooShort
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}
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/*
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* 0 1 2 3
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* 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
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* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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* | SSRC |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | fraction lost | cumulative number of packets lost |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | extended highest sequence number received |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | interarrival jitter |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | last SR (LSR) |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | delay since last SR (DLSR) |
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* +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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*/
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r.SSRC = binary.BigEndian.Uint32(rawPacket)
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r.FractionLost = rawPacket[fractionLostOffset]
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tlBytes := rawPacket[totalLostOffset:]
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r.TotalLost = uint32(tlBytes[2]) | uint32(tlBytes[1])<<8 | uint32(tlBytes[0])<<16
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r.LastSequenceNumber = binary.BigEndian.Uint32(rawPacket[lastSeqOffset:])
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r.Jitter = binary.BigEndian.Uint32(rawPacket[jitterOffset:])
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r.LastSenderReport = binary.BigEndian.Uint32(rawPacket[lastSROffset:])
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r.Delay = binary.BigEndian.Uint32(rawPacket[delayOffset:])
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return nil
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}
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func (r *ReceptionReport) len() int {
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return receptionReportLength
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}
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