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69 lines
1.4 KiB
69 lines
1.4 KiB
package rtsp
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import (
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"encoding/binary"
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)
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const (
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RTP_FIXED_HEADER_LENGTH = 12
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)
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type RTPInfo struct {
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Version int
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Padding bool
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Extension bool
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CSRCCnt int
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Marker bool
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PayloadType int
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SequenceNumber int
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Timestamp int
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SSRC int
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Payload []byte
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PayloadOffset int
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}
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func ParseRTP(rtpBytes []byte) *RTPInfo {
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if len(rtpBytes) < RTP_FIXED_HEADER_LENGTH {
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return nil
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}
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firstByte := rtpBytes[0]
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secondByte := rtpBytes[1]
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info := &RTPInfo{
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Version: int(firstByte >> 6),
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Padding: (firstByte>>5)&1 == 1,
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Extension: (firstByte>>4)&1 == 1,
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CSRCCnt: int(firstByte & 0x0f),
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Marker: secondByte>>7 == 1,
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PayloadType: int(secondByte & 0x7f),
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SequenceNumber: int(binary.BigEndian.Uint16(rtpBytes[2:])),
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Timestamp: int(binary.BigEndian.Uint32(rtpBytes[4:])),
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SSRC: int(binary.BigEndian.Uint32(rtpBytes[8:])),
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}
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offset := RTP_FIXED_HEADER_LENGTH
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end := len(rtpBytes)
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if end-offset >= 4*info.CSRCCnt {
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offset += 4 * info.CSRCCnt
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}
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if info.Extension && end-offset >= 4 {
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extLen := 4 * int(binary.BigEndian.Uint16(rtpBytes[offset+2:]))
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offset += 4
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if end-offset >= extLen {
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offset += extLen
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}
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}
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if info.Padding && end-offset > 0 {
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paddingLen := int(rtpBytes[end-1])
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if end-offset >= paddingLen {
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end -= paddingLen
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}
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}
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info.Payload = rtpBytes[offset:end]
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info.PayloadOffset = offset
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if end-offset < 1 {
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return nil
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}
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return info
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}
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