webrtc中时间戳的计算

一：视频部分：

具体函数：void VideoStreamEncoder::OnFrame(const VideoFrame& video_frame)

void VideoStreamEncoder::OnFrame(const VideoFrame& video_frame) {
  RTC_DCHECK_RUNS_SERIALIZED(&incoming_frame_race_checker_);
  VideoFrame incoming_frame = video_frame;

  // Local time in webrtc time base.
  int64_t current_time_us = clock_->TimeInMicroseconds();
  int64_t current_time_ms = current_time_us / rtc::kNumMicrosecsPerMillisec;
  // In some cases, e.g., when the frame from decoder is fed to encoder,
  // the timestamp may be set to the future. As the encoding pipeline assumes
  // capture time to be less than present time, we should reset the capture
  // timestamps here. Otherwise there may be issues with RTP send stream.
  if (incoming_frame.timestamp_us() > current_time_us)
    incoming_frame.set_timestamp_us(current_time_us);

  // Capture time may come from clock with an offset and drift from clock_.
  int64_t capture_ntp_time_ms;
  if (video_frame.ntp_time_ms() > 0) {
    capture_ntp_time_ms = video_frame.ntp_time_ms();
  } else if (video_frame.render_time_ms() != 0) {
    capture_ntp_time_ms = video_frame.render_time_ms() + delta_ntp_internal_ms_;
  } else {
    capture_ntp_time_ms = current_time_ms + delta_ntp_internal_ms_;
  }
  incoming_frame.set_ntp_time_ms(capture_ntp_time_ms);

  // Convert NTP time, in ms, to RTP timestamp.
  const int kMsToRtpTimestamp = 90;
  incoming_frame.set_timestamp(
      kMsToRtpTimestamp * static_cast(incoming_frame.ntp_time_ms()));

  if (incoming_frame.ntp_time_ms() <= last_captured_timestamp_) {
    // We don't allow the same capture time for two frames, drop this one.
    RTC_LOG(LS_WARNING) << "Same/old NTP timestamp ("
                        << incoming_frame.ntp_time_ms()
                        << " <= " << last_captured_timestamp_
                        << ") for incoming frame. Dropping.";
    return;
  }

  bool log_stats = false;
  if (current_time_ms - last_frame_log_ms_ > kFrameLogIntervalMs) {
    last_frame_log_ms_ = current_time_ms;
    log_stats = true;
  }

  last_captured_timestamp_ = incoming_frame.ntp_time_ms();
  encoder_queue_.PostTask(std::unique_ptr(new EncodeTask(
      incoming_frame, this, rtc::TimeMicros(), log_stats)));
}

 

在webrtc中的视频部分时间戳相关计算就是这个函数；

简单说明一下，可以考到函数前面的判断，也就是说，当你构造的VideoFrame设置了相关时间戳，那么这里就不计算了；

如果VideoFrame设置的video_frame.ntp_time_ms 为0， 那么这里会自动计算；

webrtc中，构造的时候就是设置为0，到这里计算；建议这么做，构造VideoFrame简单；