Set capture_time_ms using rtc::TimeMicros()

content/renderer/media/gpu/rtc_video_encoder.cc

Index: content/renderer/media/gpu/rtc_video_encoder.cc
diff --git a/content/renderer/media/gpu/rtc_video_encoder.cc b/content/renderer/media/gpu/rtc_video_encoder.cc
index 4c42938e2a4bef07048703ba1fb759c6d4448135..80e6e8e2fa40f061b819a572cd69e7bb8cdd95f6 100644
--- a/content/renderer/media/gpu/rtc_video_encoder.cc
+++ b/content/renderer/media/gpu/rtc_video_encoder.cc
@@ -234,6 +234,10 @@ class RTCVideoEncoder::Impl
   // 15 bits running index of the VP8 frames. See VP8 RTP spec for details.
   uint16_t picture_id_;
 
+  // capture_time_ms_ field of the last returned webrtc::EncodedImage from

[mcasas, 2017/02/16 19:10:15]

nit : |capture_time_ms_|

[emircan, 2017/02/16 19:41:54]

Done.

+  // BitstreamBufferReady().
+  int64_t last_capture_time_ms_;
+
   // webrtc::VideoEncoder encode complete callback.
   webrtc::EncodedImageCallback* encoded_image_callback_;
 
@@ -261,6 +265,7 @@ RTCVideoEncoder::Impl::Impl(media::GpuVideoAcceleratorFactories* gpu_factories,
       input_next_frame_(NULL),
       input_next_frame_keyframe_(false),
       output_buffers_free_count_(0),
+      last_capture_time_ms_(-1),
       encoded_image_callback_(nullptr),
       video_codec_type_(video_codec_type),
       status_(WEBRTC_VIDEO_CODEC_UNINITIALIZED) {
@@ -469,21 +474,23 @@ void RTCVideoEncoder::Impl::BitstreamBufferReady(int32_t bitstream_buffer_id,
   }
   output_buffers_free_count_--;
 
-  // Derive the capture time (in ms) and RTP timestamp (in 90KHz ticks).
-  int64_t capture_time_us, capture_time_ms;
-  uint32_t rtp_timestamp;
-
-  if (!timestamp.is_zero()) {
-    capture_time_us = timestamp.InMicroseconds();;
-    capture_time_ms = timestamp.InMilliseconds();
-  } else {
-    // Fallback to the current time if encoder does not provide timestamp.
-    capture_time_us = rtc::TimeMicros();
-    capture_time_ms = capture_time_us / base::Time::kMicrosecondsPerMillisecond;
-  }
-  // RTP timestamp can wrap around. Get the lower 32 bits.
-  rtp_timestamp = static_cast<uint32_t>(
-      capture_time_us * 90 / base::Time::kMicrosecondsPerMillisecond);
+  // Derive the capture time in ms from system clock. Make sure that it is
+  // greater than the last.
+  const int64_t capture_time_us = rtc::TimeMicros();

[mcasas, 2017/02/16 19:10:15]

Could we do all these calcuations in ms and use 
rtc::TimeMillis() here instead?  Or would that lose
precious precision?

[emircan, 2017/02/16 19:41:54]

It would lose the precision in |rtp_timestamp| calculations as we are converting
to 90 kHz there. I don't want to change anything about |rtp_timestamp| in this
CL.

+  int64_t capture_time_ms =
+      capture_time_us / base::Time::kMicrosecondsPerMillisecond;
+  if (capture_time_ms <= last_capture_time_ms_)
+    capture_time_ms = last_capture_time_ms_ + 1;

[mcasas, 2017/02/16 19:10:15]

Maybe 
  capture_time_ms = std::min(capture_time_ms, last_capture_time_ms_ + 1);
 ?
(Assuming it's OK to use the updated value of
|capture_time_ms| in l.488).

[emircan, 2017/02/16 19:41:54]

That wouldn't work. Suppose there is a rapid succession of 3 calls within the
same P ms. They would be P, P, P. We want them to be P, P+1,P+2. std::max()
would work though. 
Note that we still would want to use |capture_time_us| below as I explained
before.

+  last_capture_time_ms_ = capture_time_ms;
+
+  // Fallback to the current time if encoder does not provide timestamp.
+  const int64_t encoder_time_us =
+      timestamp.is_zero() ? capture_time_us : timestamp.InMicroseconds();
+
+  // Derive the RTP timestamp (in 90KHz ticks).  It can wrap around, get the
+  // lower 32 bits.
+  const uint32_t rtp_timestamp = static_cast<uint32_t>(
+      encoder_time_us * 90 / base::Time::kMicrosecondsPerMillisecond);
 
   webrtc::EncodedImage image(
       reinterpret_cast<uint8_t*>(output_buffer->memory()), payload_size,