RtcVideoEncoder: use the timestamp from encoder.

content/renderer/media/rtc_video_encoder.cc

Index: content/renderer/media/rtc_video_encoder.cc
diff --git a/content/renderer/media/rtc_video_encoder.cc b/content/renderer/media/rtc_video_encoder.cc
index cb7752ba848c66bb1f0957f2e07e7267341824c0..ddbe9c695969546b238ad57b4bfb41cd7443e291 100644
--- a/content/renderer/media/rtc_video_encoder.cc
+++ b/content/renderer/media/rtc_video_encoder.cc
@@ -473,17 +473,20 @@ void RTCVideoEncoder::Impl::BitstreamBufferReady(int32_t bitstream_buffer_id,
   }
   output_buffers_free_count_--;
 
-  // CrOS Nyan provides invalid timestamp. Use the current time for now.
-  // TODO(wuchengli): use the timestamp in BitstreamBufferReady after Nyan is
-  // fixed. http://crbug.com/620565.
-  const int64_t capture_time_us = rtc::TimeMicros();
-
   // Derive the capture time (in ms) and RTP timestamp (in 90KHz ticks).
-  const int64_t capture_time_ms =
-      capture_time_us / base::Time::kMicrosecondsPerMillisecond;
+  int64_t capture_time_ms;
+  uint32_t rtp_timestamp;
 
-  const uint32_t rtp_timestamp = static_cast<uint32_t>(
-      capture_time_us * 90 / base::Time::kMicrosecondsPerMillisecond);
+  if (!timestamp.is_zero()) {
+    capture_time_ms = timestamp.InMilliseconds();
+    rtp_timestamp = static_cast<uint32_t>(timestamp.InMilliseconds()) * 90;

[mcasas, 2016/06/29 14:55:50]

nit: s/timestamp.InMilliseconds()/capture_time_ms/ 
to avoid redundant function call and calculation.

[wuchengli, 2016/07/01 06:19:09]

Now I used the same calculation for both cases because I found we may lose
precision if we use milliseconds * 90. microseconds * 90 / 1000 is better.

+  } else {
+    // Fallback to the current time if encoder does not provide timestamp.
+    const int64_t capture_time_us = rtc::TimeMicros();
+    capture_time_ms = capture_time_us / base::Time::kMicrosecondsPerMillisecond;
+    rtp_timestamp = static_cast<uint32_t>(

[mcasas, 2016/06/29 14:55:50]

nit: We'd probably want |rtp_timestamp| to wrap
around if |capture_time_us| is too large, right?
(here and in l.482) If yes: add a comment for
that ? If no: consider using base::saturatedcast():

https://cs.chromium.org/chromium/src/base/numerics/safe_conversions.h?dr=C&q=...

[wuchengli, 2016/07/01 06:19:09]

Yes. We want RTC timestamp to wrap around. I added the comment.

From book "RTP: Audio and Video for the Internet":
Timestamp wrap-around is a normal part of RTP operation and should be handled by
all applications.

+        capture_time_us * 90 / base::Time::kMicrosecondsPerMillisecond);
+  }
 
   webrtc::EncodedImage image(
       reinterpret_cast<uint8_t*>(output_buffer->memory()), payload_size,
@@ -567,13 +570,15 @@ void RTCVideoEncoder::Impl::EncodeOneFrame() {
   }
 
   if (requires_copy) {
+    base::TimeDelta timestamp =

[mcasas, 2016/06/29 14:55:50]

nit: const

[wuchengli, 2016/07/01 06:19:09]

Done.

+        frame ? frame->timestamp()
+              : base::TimeDelta::FromMilliseconds(next_frame->ntp_time_ms());
     base::SharedMemory* input_buffer = input_buffers_[index];
     frame = media::VideoFrame::WrapExternalSharedMemory(
         media::PIXEL_FORMAT_I420, input_frame_coded_size_,
         gfx::Rect(input_visible_size_), input_visible_size_,
         reinterpret_cast<uint8_t*>(input_buffer->memory()),
-        input_buffer->mapped_size(), input_buffer->handle(), 0,
-        base::TimeDelta::FromMilliseconds(next_frame->ntp_time_ms()));
+        input_buffer->mapped_size(), input_buffer->handle(), 0, timestamp);
     if (!frame.get()) {
       LogAndNotifyError(FROM_HERE, "failed to create frame",
                         media::VideoEncodeAccelerator::kPlatformFailureError);