Tighten up encode time measurement in VideoProcessor.

webrtc/modules/video_coding/codecs/test/videoprocessor.cc

Index: webrtc/modules/video_coding/codecs/test/videoprocessor.cc
diff --git a/webrtc/modules/video_coding/codecs/test/videoprocessor.cc b/webrtc/modules/video_coding/codecs/test/videoprocessor.cc
index 6fb4491415df6c932f3ed6b5758a598500732e43..6b00e3c042bf2fee4832b24c3bd81b08612a365f 100644
--- a/webrtc/modules/video_coding/codecs/test/videoprocessor.cc
+++ b/webrtc/modules/video_coding/codecs/test/videoprocessor.cc
@@ -220,8 +220,6 @@ bool VideoProcessorImpl::ProcessFrame(int frame_number) {
     // Ensure we have a new statistics data object we can fill.
     FrameStatistic& stat = stats_->NewFrame(frame_number);
 
-    encode_start_ns_ = rtc::TimeNanos();
-
     // Decide if we are going to force a keyframe.
     std::vector<FrameType> frame_types(1, kVideoFrameDelta);
     if (config_.keyframe_interval > 0 &&
@@ -233,6 +231,7 @@ bool VideoProcessorImpl::ProcessFrame(int frame_number) {
     encoded_frame_size_ = 0;
     encoded_frame_type_ = kVideoFrameDelta;
 
+    encode_start_ns_ = rtc::TimeNanos();
     int32_t encode_result =
         encoder_->Encode(source_frame, nullptr, &frame_types);
 
@@ -253,6 +252,8 @@ void VideoProcessorImpl::FrameEncoded(
     webrtc::VideoCodecType codec,
     const EncodedImage& encoded_image,
     const webrtc::RTPFragmentationHeader* fragmentation) {
+  int64_t encode_stop_ns = rtc::TimeNanos();

[sprang_webrtc, 2017/02/15 10:50:59]

Maybe add comments clarifying that timestamps should be captured as close to the
start/end of encoding as possible, so that someone won't accidentally move them
close to where they're used instead, in a misguided effort to prettify the code?

[brandtr, 2017/02/15 12:13:36]

Good idea. Done.

+
   // Timestamp is frame number, so this gives us #dropped frames.
   int num_dropped_from_prev_encode =
       encoded_image._timeStamp - prev_time_stamp_ - 1;
@@ -269,8 +270,6 @@ void VideoProcessorImpl::FrameEncoded(
   // (encoder callback is only called for non-zero length frames).
   encoded_frame_size_ = encoded_image._length;
   encoded_frame_type_ = encoded_image._frameType;
-
-  int64_t encode_stop_ns = rtc::TimeNanos();
   int frame_number = encoded_image._timeStamp;
 
   FrameStatistic& stat = stats_->stats_[frame_number];