Simplify AudioSplicer logic which slots buffers before or after a splice point.

media/base/audio_splicer.h

 // Copyright (c) 2012 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.
 
 #ifndef MEDIA_BASE_AUDIO_SPLICER_H_
 #define MEDIA_BASE_AUDIO_SPLICER_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
@@ skipping 27 matching lines @@
   // occurred.
   bool AddInput(const scoped_refptr<AudioBuffer>& input);
 
   // Returns true if the splicer has a buffer to return.
   bool HasNextBuffer() const;
 
   // Removes the next buffer from the output buffer queue and returns it; this
   // should only be called if HasNextBuffer() returns true.
   scoped_refptr<AudioBuffer> GetNextBuffer();
 
-  // Indicates that overlapping buffers are coming up and should be crossfaded.
-  // Once set, all buffers encountered after |splice_timestamp| will be queued
-  // internally until at least 5ms of overlapping buffers are received (or end
-  // of stream, whichever comes first).
+  // Indicates an upcoming splice point.  All buffers overlapping or after the
+  // |splice_timestamp| will be considered as "before the splice."  Clients must
+  // then call SetSpliceTimestamp(kNoTimestamp()) to signal that future buffers
+  // should be considered as "after the splice."
+  //
+  // Once |kCrossfadeDurationInMilliseconds| of buffers "after the splice" or
+  // end of stream has been received, the "after" buffers will be crossfaded
+  // with all "before" buffers which overlap them.  "before" buffers outside
+  // of the overlap range will be discarded.

[wolenetz, 2014/04/17 22:29:30]

This "discard" logic: where is it? I see that l.287 of audio_splicer.cc feeds
these to the output. By 'buffers', are decoded frames meant, instead (and the
discard happens in ExtractCrossfadeFromPreSplice()?)

[DaleCurtis, 2014/04/17 23:52:33]

The discard of unused pre splice buffers happens on l.475 of audio_splicer.cc 

   void SetSpliceTimestamp(base::TimeDelta splice_timestamp);
 
  private:
   friend class AudioSplicerTest;
 
   // Extracts frames to be crossfaded from |pre_splice_sanitizer_|.  Transfers
   // all frames before |splice_timestamp_| into |output_sanitizer_| and drops
   // frames outside of the crossfade duration.
   //
   // The size of the returned AudioBus is the crossfade duration in frames.
@@ skipping 32 matching lines @@
   // crossfading are received the pre and post sanitizers are drained into
   // |output_sanitizer_| by the two ExtractCrossfadeFromXXX methods above.
   //
   // |pre_splice_sanitizer_| is not constructed until the first splice frame is
   // encountered.  At which point it is constructed based on the timestamp state
   // of |output_sanitizer_|.  It is destructed once the splice is finished.
   scoped_ptr<AudioStreamSanitizer> output_sanitizer_;
   scoped_ptr<AudioStreamSanitizer> pre_splice_sanitizer_;
   scoped_ptr<AudioStreamSanitizer> post_splice_sanitizer_;
 
+  // Whether all buffers which should go into |pre_splice_sanitizer_| have been
+  // received.  If true, buffers should now be put in |post_splice_sanitizer_|.
+  bool have_all_pre_splice_buffers_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(AudioSplicer);
 };
 
 }  // namespace media
 
 #endif