Add stronger DCHECK for front and back timestamp calculations.

media/filters/audio_clock.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/audio_clock.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "media/base/buffers.h"
@@ skipping 24 matching lines @@
 
   // First write: initialize buffer with silence.
   if (start_timestamp_ == front_timestamp_ && buffered_.empty())
     PushBufferedAudioData(delay_frames, 0.0);
 
   // Move frames from |buffered_| into the computed timestamp based on
   // |delay_frames|.
   //
   // The ordering of compute -> push -> pop eliminates unnecessary memory
   // reallocations in cases where |buffered_| gets emptied.
+  const int64_t original_buffered_frames = total_buffered_frames_;

[jrummell, 2015/07/10 00:32:57]

Since this is only used in the DCHECK, will a release build complain about
unused variable?

[DaleCurtis, 2015/07/10 00:34:22]

Nope, the DCHECK still counts as usage.

   int64_t frames_played =
       std::max(INT64_C(0), total_buffered_frames_ - delay_frames);
   front_timestamp_ += ComputeBufferedMediaTime(frames_played);
   PushBufferedAudioData(frames_written, playback_rate);
   PushBufferedAudioData(frames_requested - frames_written, 0.0);
   PopBufferedAudioData(frames_played);
 
   back_timestamp_ += base::TimeDelta::FromMicroseconds(
       frames_written * playback_rate * microseconds_per_frame_);
 
+  // Ensure something crazy hasn't happened to desync the front and back values.
+  DCHECK_LE(front_timestamp_.InMicroseconds(), back_timestamp_.InMicroseconds())
+      << "frames_written=" << frames_written
+      << ", frames_requested=" << frames_requested
+      << ", delay_frames=" << delay_frames
+      << ", playback_rate=" << playback_rate
+      << ", frames_played=" << frames_played
+      << ", original_buffered_frames=" << original_buffered_frames
+      << ", total_buffered_frames_=" << total_buffered_frames_;
+
   // Update cached values.
   double scaled_frames = 0;
   double scaled_frames_at_same_rate = 0;
   bool found_silence = false;
   for (size_t i = 0; i < buffered_.size(); ++i) {
     if (buffered_[i].playback_rate == 0) {
       found_silence = true;
       continue;
     }
 
@@ skipping 110 matching lines @@
     int64_t min_frames = std::min(buffered_[i].frames, frames);
     scaled_frames += min_frames * buffered_[i].playback_rate;
     frames -= min_frames;
   }
 
   return base::TimeDelta::FromMicroseconds(scaled_frames *
                                            microseconds_per_frame_);
 }
 
 }  // namespace media