Reduce jitter from uneven SincResampler buffer size requests.

media/base/multi_channel_resampler.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_MULTI_CHANNEL_RESAMPLER_H_
 #define MEDIA_BASE_MULTI_CHANNEL_RESAMPLER_H_
 
 #include <vector>
 
 #include "base/callback.h"
@@ skipping 11 matching lines @@
   // Callback type for providing more data into the resampler.  Expects AudioBus
   // to be completely filled with data upon return; zero padded if not enough
   // frames are available to satisfy the request.  |frame_delay| is the number
   // of output frames already processed and can be used to estimate delay.
   typedef base::Callback<void(int frame_delay, AudioBus* audio_bus)> ReadCB;
 
   // Constructs a MultiChannelResampler with the specified |read_cb|, which is
   // used to acquire audio data for resampling.  |io_sample_rate_ratio| is the
   // ratio of input / output sample rates.
   MultiChannelResampler(int channels, double io_sample_rate_ratio,
-                        const ReadCB& read_cb);
+                        size_t request_size, const ReadCB& read_cb);

[henrika (OOO until Aug 14), 2013/04/27 19:43:40]

Perhaps add a comment about the new parameter?

[Sergey Ulanov, 2013/04/29 06:23:37]

nit: one argument per line please:
http://www.chromium.org/developers/coding-style#Code_Formatting

It's not clear if request_size is in bytes or samples. Perhaps it should be
called request_samples?

[DaleCurtis, 2013/04/29 22:12:31]

Renamed to request_frames and added a comment.

   virtual ~MultiChannelResampler();
 
   // Resamples |frames| of data from |read_cb_| into AudioBus.
   void Resample(AudioBus* audio_bus, int frames);

[Chris Rogers, 2013/04/28 19:50:56]

Wouldn't it be better to try to get the callback size to be exactly (or within
one sample-frame) of the amount expected based on |frames| and the
|io_sample_rate_ratio|, instead of always using the same |request_size| as
you're doing here?  For example, if the ratio is 44100/48000 and you ask to
render 480 frames here, then it will call you back asking for 441.  In the
general case it should always be able to be +/- 1 or 2 from the exact amount.

You might want to try instrumenting the AUVarispeed to see how it handles the
requests for more data, I seem to remember it behaves more like this.

[Sergey Ulanov, 2013/04/29 06:23:37]

unrelated nit: output parameters should be after input parameters:
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Functi...

[DaleCurtis, 2013/04/29 18:50:04]

Practically I think it amounts to the same thing in almost all cases, except for
possibly hurting mildly in AudioOutputResampler && TabCapture cases, and would
also be a bit harder to implement.

Only <audio> uses disable_fifo which is where your suggestion would help most
(simply in reducing callback counts for abnormal buffer sizes) -- even in that
case we may not want to use the output request size if it's huge and we're
decoding complex material (2048 and 192kHz multichannel for instance).

With a FIFO it doesn't really matter if we request 50 frames twice or 70 frames
once since it'll still result in two callbacks.  Disregarding the added FIFO
overhead: in the best case your solution is the same as my solution; in the
worst, it will hurt mildly worse if it causes back to back requests without the
delay of Convolve() in between.

Finally it's a bit harder to implement because either: we'd need to reallocate
input buffers and resize ranges to handle frame size changes.  Or, since we
don't support frame size changes, refactor Convert() and Resample() to take
their frame sizes during construction.

[DaleCurtis, 2013/04/29 22:12:31]

Done.

 
   // Flush all buffered data and reset internal indices.  Not thread safe, do
   // not call while Resample() is in progress.
   void Flush();
 
   // Update ratio for all SincResamplers.  SetRatio() will cause reconstruction
   // of the kernels used for resampling.  Not thread safe, do not call while
   // Resample() is in progress.
   void SetRatio(double io_sample_rate_ratio);
 
@@ skipping 20 matching lines @@
   // The number of output frames that have successfully been processed during
   // the current Resample() call.
   int output_frames_ready_;
 
   DISALLOW_COPY_AND_ASSIGN(MultiChannelResampler);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_MULTI_CHANNEL_RESAMPLER_H_