114 lines
2.7 KiB
Go
114 lines
2.7 KiB
Go
package rtcp
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import (
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"encoding/binary"
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"fmt"
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"math"
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)
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// SLIEntry represents a single entry to the SLI packet's
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// list of lost slices.
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type SLIEntry struct {
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// ID of first lost slice
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First uint16
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// Number of lost slices
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Number uint16
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// ID of related picture
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Picture uint8
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}
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// The SliceLossIndication packet informs the encoder about the loss of a picture slice
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type SliceLossIndication struct {
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// SSRC of sender
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SenderSSRC uint32
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// SSRC of the media source
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MediaSSRC uint32
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SLI []SLIEntry
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}
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const (
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sliLength = 2
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sliOffset = 8
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)
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// Marshal encodes the SliceLossIndication in binary
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func (p SliceLossIndication) Marshal() ([]byte, error) {
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if len(p.SLI)+sliLength > math.MaxUint8 {
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return nil, errTooManyReports
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}
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rawPacket := make([]byte, sliOffset+(len(p.SLI)*4))
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binary.BigEndian.PutUint32(rawPacket, p.SenderSSRC)
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binary.BigEndian.PutUint32(rawPacket[4:], p.MediaSSRC)
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for i, s := range p.SLI {
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sli := ((uint32(s.First) & 0x1FFF) << 19) |
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((uint32(s.Number) & 0x1FFF) << 6) |
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(uint32(s.Picture) & 0x3F)
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binary.BigEndian.PutUint32(rawPacket[sliOffset+(4*i):], sli)
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}
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hData, err := p.Header().Marshal()
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if err != nil {
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return nil, err
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}
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return append(hData, rawPacket...), nil
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}
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// Unmarshal decodes the SliceLossIndication from binary
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func (p *SliceLossIndication) Unmarshal(rawPacket []byte) error {
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if len(rawPacket) < (headerLength + ssrcLength) {
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return errPacketTooShort
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}
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var h Header
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if err := h.Unmarshal(rawPacket); err != nil {
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return err
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}
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if len(rawPacket) < (headerLength + int(4*h.Length)) {
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return errPacketTooShort
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}
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if h.Type != TypeTransportSpecificFeedback || h.Count != FormatSLI {
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return errWrongType
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}
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p.SenderSSRC = binary.BigEndian.Uint32(rawPacket[headerLength:])
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p.MediaSSRC = binary.BigEndian.Uint32(rawPacket[headerLength+ssrcLength:])
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for i := headerLength + sliOffset; i < (headerLength + int(h.Length*4)); i += 4 {
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sli := binary.BigEndian.Uint32(rawPacket[i:])
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p.SLI = append(p.SLI, SLIEntry{
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First: uint16((sli >> 19) & 0x1FFF),
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Number: uint16((sli >> 6) & 0x1FFF),
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Picture: uint8(sli & 0x3F),
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})
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}
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return nil
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}
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func (p *SliceLossIndication) len() int {
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return headerLength + sliOffset + (len(p.SLI) * 4)
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}
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// Header returns the Header associated with this packet.
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func (p *SliceLossIndication) Header() Header {
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return Header{
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Count: FormatSLI,
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Type: TypeTransportSpecificFeedback,
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Length: uint16((p.len() / 4) - 1),
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}
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}
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func (p *SliceLossIndication) String() string {
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return fmt.Sprintf("SliceLossIndication %x %x %+v", p.SenderSSRC, p.MediaSSRC, p.SLI)
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}
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// DestinationSSRC returns an array of SSRC values that this packet refers to.
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func (p *SliceLossIndication) DestinationSSRC() []uint32 {
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return []uint32{p.MediaSSRC}
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}
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