79 lines
1.8 KiB
Go
79 lines
1.8 KiB
Go
package rtp
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import (
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"time"
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)
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const (
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absSendTimeExtensionSize = 3
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)
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// AbsSendTimeExtension is a extension payload format in
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// http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
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type AbsSendTimeExtension struct {
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Timestamp uint64
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}
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// Marshal serializes the members to buffer.
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func (t *AbsSendTimeExtension) Marshal() ([]byte, error) {
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return []byte{
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byte(t.Timestamp & 0xFF0000 >> 16),
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byte(t.Timestamp & 0xFF00 >> 8),
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byte(t.Timestamp & 0xFF),
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}, nil
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}
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// Unmarshal parses the passed byte slice and stores the result in the members.
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func (t *AbsSendTimeExtension) Unmarshal(rawData []byte) error {
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if len(rawData) < absSendTimeExtensionSize {
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return errTooSmall
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}
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t.Timestamp = uint64(rawData[0])<<16 | uint64(rawData[1])<<8 | uint64(rawData[2])
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return nil
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}
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// Estimate absolute send time according to the receive time.
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// Note that if the transmission delay is larger than 64 seconds, estimated time will be wrong.
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func (t *AbsSendTimeExtension) Estimate(receive time.Time) time.Time {
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receiveNTP := toNtpTime(receive)
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ntp := receiveNTP&0xFFFFFFC000000000 | (t.Timestamp&0xFFFFFF)<<14
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if receiveNTP < ntp {
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// Receive time must be always later than send time
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ntp -= 0x1000000 << 14
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}
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return toTime(ntp)
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}
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// NewAbsSendTimeExtension makes new AbsSendTimeExtension from time.Time.
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func NewAbsSendTimeExtension(sendTime time.Time) *AbsSendTimeExtension {
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return &AbsSendTimeExtension{
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Timestamp: toNtpTime(sendTime) >> 14,
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}
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}
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func toNtpTime(t time.Time) uint64 {
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var s uint64
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var f uint64
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u := uint64(t.UnixNano())
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s = u / 1e9
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s += 0x83AA7E80 // offset in seconds between unix epoch and ntp epoch
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f = u % 1e9
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f <<= 32
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f /= 1e9
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s <<= 32
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return s | f
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}
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func toTime(t uint64) time.Time {
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s := t >> 32
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f := t & 0xFFFFFFFF
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f *= 1e9
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f >>= 32
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s -= 0x83AA7E80
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u := s*1e9 + f
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return time.Unix(0, int64(u))
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}
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