Revert 258215 "Remove muting for extreme playbackRates."

trunk/src/media/filters/audio_renderer_algorithm.cc

Index: trunk/src/media/filters/audio_renderer_algorithm.cc
===================================================================
--- trunk/src/media/filters/audio_renderer_algorithm.cc	(revision 274695)
+++ trunk/src/media/filters/audio_renderer_algorithm.cc	(working copy)
@@ -46,6 +46,12 @@
 //    |search_block_index_| = |search_block_center_offset_| -
 //        |search_block_center_offset_|.
 
+// Max/min supported playback rates for fast/slow audio. Audio outside of these
+// ranges are muted.
+// Audio at these speeds would sound better under a frequency domain algorithm.
+static const float kMinPlaybackRate = 0.5f;
+static const float kMaxPlaybackRate = 4.0f;
+
 // Overlap-and-add window size in milliseconds.
 static const int kOlaWindowSizeMs = 20;
 
@@ -70,6 +76,8 @@
     : channels_(0),
       samples_per_second_(0),
       playback_rate_(0),
+      muted_(false),
+      muted_partial_frame_(0),
       capacity_(kStartingBufferSizeInFrames),
       output_time_(0.0),
       search_block_center_offset_(0),
@@ -143,6 +151,31 @@
 
   DCHECK_EQ(channels_, dest->channels());
 
+  // Optimize the |muted_| case to issue a single clear instead of performing
+  // the full crossfade and clearing each crossfaded frame.
+  if (muted_) {
+    int frames_to_render =
+        std::min(static_cast<int>(audio_buffer_.frames() / playback_rate_),
+                 requested_frames);
+
+    // Compute accurate number of frames to actually skip in the source data.
+    // Includes the leftover partial frame from last request. However, we can
+    // only skip over complete frames, so a partial frame may remain for next
+    // time.
+    muted_partial_frame_ += frames_to_render * playback_rate_;
+    int seek_frames = static_cast<int>(muted_partial_frame_);
+    dest->ZeroFrames(frames_to_render);
+    audio_buffer_.SeekFrames(seek_frames);
+
+    // Determine the partial frame that remains to be skipped for next call. If
+    // the user switches back to playing, it may be off time by this partial
+    // frame, which would be undetectable. If they subsequently switch to
+    // another playback rate that mutes, the code will attempt to line up the
+    // frames again.
+    muted_partial_frame_ -= seek_frames;
+    return frames_to_render;
+  }
+
   int slower_step = ceil(ola_window_size_ * playback_rate_);
   int faster_step = ceil(ola_window_size_ / playback_rate_);
 
@@ -167,6 +200,8 @@
 void AudioRendererAlgorithm::SetPlaybackRate(float new_rate) {
   DCHECK_GE(new_rate, 0);
   playback_rate_ = new_rate;
+  muted_ =
+      playback_rate_ < kMinPlaybackRate || playback_rate_ > kMaxPlaybackRate;
 }
 
 void AudioRendererAlgorithm::FlushBuffers() {