[Video] Fix keyframe distance average calculations.

media/filters/decoder_stream_traits.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/filters/decoder_stream_traits.h"
 
 #include <limits>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 89 matching lines @@
     const scoped_refptr<MediaLog>& media_log)
     // Randomly selected number of samples to keep.
     : keyframe_distance_average_(16) {}
 
 void DecoderStreamTraits<DemuxerStream::VIDEO>::ReportStatistics(
     const StatisticsCB& statistics_cb,
     int bytes_decoded) {
   PipelineStatistics statistics;
   statistics.video_bytes_decoded = bytes_decoded;
 
-  // Before we have enough keyframes to calculate the average distance, we will
-  // assume the average keyframe distance is infinitely large.
-  if (keyframe_distance_average_.count() < 3) {
-    statistics.video_keyframe_distance_average = base::TimeDelta::Max();
-  } else {
+  if (keyframe_distance_average_.count()) {
     statistics.video_keyframe_distance_average =
         keyframe_distance_average_.Average();
+  } else {
+    // Before we have enough keyframes to calculate the average distance, we
+    // will assume the average keyframe distance is infinitely large.
+    statistics.video_keyframe_distance_average = base::TimeDelta::Max();
   }
 
   statistics_cb.Run(statistics);
 }
 
 void DecoderStreamTraits<DemuxerStream::VIDEO>::InitializeDecoder(
     DecoderType* decoder,
     DemuxerStream* stream,
     CdmContext* cdm_context,
     const InitCB& init_cb,
     const OutputCB& output_cb) {
   DCHECK(stream->video_decoder_config().IsValidConfig());
   decoder->Initialize(stream->video_decoder_config(),
                       stream->liveness() == DemuxerStream::LIVENESS_LIVE,
                       cdm_context, init_cb, output_cb);
 }
 
 void DecoderStreamTraits<DemuxerStream::VIDEO>::OnStreamReset(
     DemuxerStream* stream) {
   DCHECK(stream);
   last_keyframe_timestamp_ = base::TimeDelta();
-  keyframe_distance_average_.Reset();
 }
 
 void DecoderStreamTraits<DemuxerStream::VIDEO>::OnDecode(
     const scoped_refptr<DecoderBuffer>& buffer) {
   if (!buffer)
     return;
 
   if (buffer->end_of_stream()) {
     last_keyframe_timestamp_ = base::TimeDelta();
     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 frame_distance =
       current_frame_timestamp - last_keyframe_timestamp_;
   UMA_HISTOGRAM_MEDIUM_TIMES("Media.Video.KeyFrameDistance", frame_distance);
   last_keyframe_timestamp_ = current_frame_timestamp;
   keyframe_distance_average_.AddSample(frame_distance);
 }
 
 }  // namespace media