Fix muted audio when playback rate != 1.0 or 0.0

media/filters/audio_renderer_algorithm_base.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.
 
 // AudioRendererAlgorithmBase buffers and transforms audio data. The owner of
 // this object provides audio data to the object through EnqueueBuffer() and
 // requests data from the buffer via FillBuffer(). The owner also sets the
 // playback rate, and the AudioRendererAlgorithm will stretch or compress the
 // buffered audio as necessary to match the playback rate when fulfilling
 // FillBuffer() requests. AudioRendererAlgorithm can request more data to be
@@ skipping 33 matching lines @@
   // Initializes this object with information about the audio stream.
   // |samples_per_second| is in Hz. |read_request_callback| is called to
   // request more data from the client, requests that are fulfilled through
   // calls to EnqueueBuffer().
   void Initialize(int channels,
                   int samples_per_second,
                   int bits_per_channel,
                   float initial_playback_rate,
                   const base::Closure& request_read_cb);
 
-  // Tries to fill |length| bytes of |dest| with possibly scaled data from our
-  // |audio_buffer_|. Data is scaled based on the playback rate, using a
-  // variation of the Overlap-Add method to combine sample windows.
+  // Tries to fill |requested_frames| frames into |dest| with possibly scaled
+  // data from our |audio_buffer_|. Data is scaled based on the playback rate,
+  // using a variation of the Overlap-Add method to combine sample windows.
   //
   // Data from |audio_buffer_| is consumed in proportion to the playback rate.
-  // FillBuffer() will fit |playback_rate_| * |length| bytes of raw data from
-  // |audio_buffer| into |length| bytes of output data in |dest| by chopping up
-  // the buffered data into windows and crossfading from one window to the next.
-  // For speeds greater than 1.0f, FillBuffer() "squish" the windows, dropping
-  // some data in between windows to meet the sped-up playback. For speeds less
-  // than 1.0f, FillBuffer() will "stretch" the window by copying and
-  // overlapping data at the window boundaries, crossfading in between.
   //
-  // Returns the number of bytes copied into |dest|.
+  // Returns the number of frames copied into |dest|.
   // May request more reads via |request_read_cb_| before returning.
-  uint32 FillBuffer(uint8* dest, uint32 length);
+  uint32 FillBuffer(uint8* dest, uint32 requested_frames);
 
   // Clears |audio_buffer_|.
   void FlushBuffers();
 
   // Returns the time of the next byte in our data or kNoTimestamp() if current
   // time is unknown.
   base::TimeDelta GetTime();
 
   // Enqueues a buffer. It is called from the owner of the algorithm after a
   // read completes.
   void EnqueueBuffer(Buffer* buffer_in);
 
   float playback_rate() const { return playback_rate_; }
   void SetPlaybackRate(float new_rate);
 
-  // Returns whether |audio_buffer_| is empty.
+  // Returns whether the algorithm needs more data to continue filling buffers.
+  bool NeedsMoreData();
+
+  // Returns true if |audio_buffer_| is empty.
   bool IsQueueEmpty();
 
   // Returns true if |audio_buffer_| is at or exceeds capacity.
   bool IsQueueFull();
 
   // Returns the capacity of |audio_buffer_|.
   uint32 QueueCapacity();
 
   // Increase the capacity of |audio_buffer_| if possible.
   void IncreaseQueueCapacity();
 
   // Returns the number of bytes left in |audio_buffer_|, which may be larger
   // than QueueCapacity() in the event that a read callback delivered more data
   // than |audio_buffer_| was intending to hold.
   uint32 bytes_buffered() { return audio_buffer_.forward_bytes(); }
 
   uint32 window_size() { return window_size_; }
 
  private:
-  // Advances |audio_buffer_|'s internal pointer by |bytes|.
-  void AdvanceBufferPosition(uint32 bytes);
+  // Fills |dest| with one frame of audio data at normal speed. Returns true if
+  // a frame was rendered, false otherwise.
+  bool OutputNormalPlayback(uint8* dest);
 
-  // Tries to copy |bytes| bytes from |audio_buffer_| to |dest|.
-  // Returns the number of bytes successfully copied.
-  uint32 CopyFromAudioBuffer(uint8* dest, uint32 bytes);
+  // Fills |dest| with one frame of audio data at faster than normal speed.
+  // Returns true if a frame was rendered, false otherwise.
+  //
+  // When the audio playback is > 1.0, we use a variant of Overlap-Add to squish
+  // audio output while preserving pitch. Essentially, we play a bit of audio
+  // data at normal speed, then we "fast forward" by dropping the next bit of
+  // audio data, and then we stich the pieces together by crossfading from one
+  // audio chunk to the next.
+  bool OutputFasterPlayback(uint8* dest);
+
+  // Fills |dest| with one frame of audio data at slower than normal speed.
+  // Returns true if a frame was rendered, false otherwise.
+  //
+  // When the audio playback is > 1.0, we use a variant of Overlap-Add to

[acolwell GONE FROM CHROMIUM, 2012/02/22 07:51:40]

is < 1.0 ?

[vrk (LEFT CHROMIUM), 2012/02/23 20:33:06]

Whoops, yes! Done.

+  // stretch audio output while preserving pitch. This works by outputting a
+  // segment of audio data at normal speed. The next audio segment then starts
+  // by repeating some of the audio data from the previous audio segment.
+  // Segments are stiched together by crossfading from one audio chunk to the
+  // next.
+  bool OutputSlowerPlayback(uint8* dest);
+
+  // Resets the window state to the start of a new window.
+  void ResetWindow();
+
+  // Copies a raw frame from |audio_buffer_| into |dest| without progressing
+  // |audio_buffer_|'s internal "current" cursor. Optionally peeks at a forward
+  // byte |offset|.
+  void PeekRawFrame(uint8* dest);

[acolwell GONE FROM CHROMIUM, 2012/02/22 07:51:40]

nit: Rename to CopyWithoutAdvance or something similar? I think that would make
the name closer to what the comment indicates.

[vrk (LEFT CHROMIUM), 2012/02/23 20:33:06]

Much better name, thanks! Done.

+  void PeekRawFrame(uint8* dest, uint32 offset);
+
+  // Copies a raw frame from |audio_buffer_| into |dest| and progresses the
+  // |audio_buffer_| forward.
+  void ReadRawFrame(uint8* dest);

[acolwell GONE FROM CHROMIUM, 2012/02/22 07:51:40]

nit: Rename to CopyWithAdvance to be more descriptive and contrast with the
methods above?

[vrk (LEFT CHROMIUM), 2012/02/23 20:33:06]

Done.

+
+  // Moves the |audio_buffer_| forward by one frame.
+  void DropFrame();
+
+  // Does a linear crossfade from |intro| into |outtro| for one frame.
+  // Assumes pointers are valid and are at least size of |bytes_per_frame_|.
+  void OutputCrossfadedFrame(uint8* outtro, const uint8* intro);
+  template <class Type>
+  void CrossfadeFrame(Type* outtro, const Type* intro);
 
   // Aligns |value| to a channel and sample boundary.

[acolwell GONE FROM CHROMIUM, 2012/02/22 07:51:40]

nit: How about "Round |*value| down to the nearest frame boundry." ?

[vrk (LEFT CHROMIUM), 2012/02/23 20:33:06]

Done.

-  void AlignToSampleBoundary(uint32* value);
-
-  // Attempts to write |length| bytes of muted audio into |dest|.
-  uint32 MuteBuffer(uint8* dest, uint32 length);
+  void AlignToFrameBoundary(uint32* value);
 
   // Number of channels in audio stream.
   int channels_;
 
   // Sample rate of audio stream.
   int samples_per_second_;
 
   // Byte depth of audio.
   int bytes_per_channel_;
 
   // Used by algorithm to scale output.
   float playback_rate_;
 
   // Used to request more data.
   base::Closure request_read_cb_;
 
   // Buffered audio data.
   SeekableBuffer audio_buffer_;
 
   // Length for crossfade in bytes.
-  uint32 crossfade_size_;
+  uint32 bytes_in_crossfade_;
+
+  // Length of frame in bytes.
+  uint32 bytes_per_frame_;
+
+  // The current location in the audio window, between 0 and |window_size_|.
+  // When |index_into_window_| reaches |window_size_|, the window resets.
+  // Indexed by byte.
+  uint32 index_into_window_;
+
+  // The frame number in the crossfade.
+  uint32 crossfade_frame_number_;
+
+  // True if the audio should be muted.
+  bool muted_;
+
+  bool needs_more_data_;
+
+  // Temporary buffer to hold crossfade data.
+  scoped_array<uint8> crossfade_buffer_;
 
   // Window size, in bytes (calculated from audio properties).
   uint32 window_size_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererAlgorithmBase);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_AUDIO_RENDERER_ALGORITHM_BASE_H_