[Video] Collect average keyframe distance for video

media/filters/decoder_stream_traits.cc

Index: media/filters/decoder_stream_traits.cc
diff --git a/media/filters/decoder_stream_traits.cc b/media/filters/decoder_stream_traits.cc
index ec6c7993a1464c4c1347ae0af971a8ad288d85e8..7d0076cce4be1b02a5dcb6f8091f7f142db9186c 100644
--- a/media/filters/decoder_stream_traits.cc
+++ b/media/filters/decoder_stream_traits.cc
@@ -5,6 +5,7 @@
 #include "media/filters/decoder_stream_traits.h"
 
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "media/base/audio_buffer.h"
 #include "media/base/audio_decoder.h"
 #include "media/base/audio_decoder_config.h"
@@ -103,6 +104,11 @@ scoped_refptr<DecoderStreamTraits<DemuxerStream::VIDEO>::OutputType>
   return OutputType::CreateEOSFrame();
 }
 
+// The samples count for keyframe distance average is picked arbitrarily.

[DaleCurtis, 2016/12/06 21:31:04]

Generally just put over the variable name.

+DecoderStreamTraits<DemuxerStream::VIDEO>::DecoderStreamTraits(
+    const scoped_refptr<MediaLog>& media_log)
+    : keyframe_distance_average_(10) {}
+
 void DecoderStreamTraits<DemuxerStream::VIDEO>::InitializeDecoder(
     DecoderType* decoder,
     DemuxerStream* stream,
@@ -115,4 +121,47 @@ void DecoderStreamTraits<DemuxerStream::VIDEO>::InitializeDecoder(
                       cdm_context, init_cb, output_cb);
 }
 
+void DecoderStreamTraits<DemuxerStream::VIDEO>::OnStreamReset(
+    DemuxerStream* stream) {
+  DCHECK(stream);
+  ResetMetrics();
+  max_average_ = base::TimeDelta();
+}
+
+void DecoderStreamTraits<DemuxerStream::VIDEO>::OnDecode(
+    const scoped_refptr<DecoderBuffer>& buffer) {
+  if (!buffer)
+    return;
+
+  if (buffer->end_of_stream()) {
+    ResetMetrics();
+    return;
+  }
+
+  if (!buffer->is_key_frame())
+    return;
+
+  base::TimeDelta current_frame_timestamp = buffer->timestamp();
+  if (last_keyframe_timestamp_.is_zero()) {
+    last_keyframe_timestamp_ = current_frame_timestamp;
+    return;
+  }
+
+  base::TimeDelta last_keyframe_distance =
+      current_frame_timestamp - last_keyframe_timestamp_;
+  last_keyframe_timestamp_ = current_frame_timestamp;
+  keyframe_distance_average_.AddSample(last_keyframe_distance);
+  base::TimeDelta new_average = keyframe_distance_average_.Average();
+  if (new_average > max_average_) {
+    max_average_ = new_average;
+    UMA_HISTOGRAM_MEDIUM_TIMES("Media.Video.KeyFrameDistanceAverage",
+                               new_average);
+  }
+}
+
+void DecoderStreamTraits<DemuxerStream::VIDEO>::ResetMetrics() {
+  keyframe_distance_average_.Reset();
+  last_keyframe_timestamp_ = base::TimeDelta();
+}
+
 }  // namespace media