Improving WebM video duration estimation.

media/formats/webm/webm_cluster_parser.h

Index: media/formats/webm/webm_cluster_parser.h
diff --git a/media/formats/webm/webm_cluster_parser.h b/media/formats/webm/webm_cluster_parser.h
index 759fba9d6341800a6e58d1793435fdc03b11ef91..5a6fe176d0152c706ca5754e40596da07149853b 100644
--- a/media/formats/webm/webm_cluster_parser.h
+++ b/media/formats/webm/webm_cluster_parser.h
@@ -31,7 +31,7 @@ class MEDIA_EXPORT WebMClusterParser : public WebMParserClient {
   // set and there is not enough information to get a better estimate.
   enum {
     kDefaultAudioBufferDurationInMs = 23,  // Common 1k samples @44.1kHz
-    kDefaultVideoBufferDurationInMs = 42  // Low 24fps to reduce stalls
+    kDefaultVideoBufferDurationInMs = 63   // Low 16fps to reduce stalls

[wolenetz, 2015/03/28 00:26:06]

nit: comment here (and elaborate in CL description) that, in combination with
compliant coded frame processing discontinuity detection logic, this mitigates
videos with framerates as low as 8fps (max 0.125ms timestamp delta) causing gaps
when this estimate is used (though not in all cases, like varying frame-rate
streams, since we might have already determined a lesser estimate from previous
frames).

[chcunningham, 2015/04/13 23:25:18]

Done.

   };
 
   // Opus packets encode the duration and other parameters in the 5 most
@@ -72,8 +72,8 @@ class MEDIA_EXPORT WebMClusterParser : public WebMParserClient {
     bool AddBuffer(const scoped_refptr<StreamParserBuffer>& buffer);
 
     // If |last_added_buffer_missing_duration_| is set, updates its duration to
-    // be non-kNoTimestamp() value of |estimated_next_frame_duration_| or an
-    // arbitrary default, then adds it to |buffers_| and unsets
+    // be non-kNoTimestamp() value of |estimated_next_frame_duration_| or a
+    // hard-coded default, then adds it to |buffers_| and unsets
     // |last_added_buffer_missing_duration_|. (This method helps stream parser
     // emit all buffers in a media segment before signaling end of segment.)
     void ApplyDurationEstimateIfNeeded();
@@ -107,6 +107,10 @@ class MEDIA_EXPORT WebMClusterParser : public WebMParserClient {
     // ApplyDurationEstimateIfNeeded().
     base::TimeDelta GetDurationEstimate();
 
+    // Counts the number of estimated durations used in this track. Used to
+    // prevent log spam for MEDIA_LOG()s about estimated duration.
+    int num_duration_estimates_;
+
     int track_num_;
     bool is_video_;
 
@@ -129,8 +133,10 @@ class MEDIA_EXPORT WebMClusterParser : public WebMParserClient {
     base::TimeDelta default_duration_;
 
     // If kNoTimestamp(), then a default value will be used. This estimate is
-    // the maximum duration seen or derived so far for this track, and is valid
-    // only if |default_duration_| is kNoTimestamp().
+    // the maximum (for video), or minimum (for audio) duration seen so far for
+    // this track, and is used only if |default_duration_| is kNoTimestamp().
+    // TODO(chcunningham): Use maximum for audio too, adding checks to disable
+    // splicing when these estimates are observed in SourceBufferStream.
     base::TimeDelta estimated_next_frame_duration_;
 
     LogCB log_cb_;