Add the option of compressing speech input audio using FLAC.

Add the option of compressing speech input audio using FLAC.
In the process, added a generic AudioEncoder interface which could create the requested codec.
Right now the codec is set to FLAC. In a future CL, we'll determine the codec to use dynamically
based on bandwidth considerations.

This CL depends on http://codereview.chromium.org/6205006/ going in first.

BUG=61677
TEST=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=71599

[bulach, 2011-01-12 16:27:07]

LGTM

nice refactoring! mostly nits and suggestions below:

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
File chrome/browser/speech/audio_encoder.cc (right):

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.cc:30: const FLAC__StreamEncoder *encoder,
s/r *e/r* e/

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.cc:37: FLAC__StreamEncoder *encoder_;
s/r *e/r* e/

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.cc:44: const FLAC__StreamEncoder *encoder,
ok, few places then.. :)

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.cc:167: audio_buffers_.clear();
STLDeleteElements from stl_util-inl.h

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.cc:176: it != audio_buffers_.end(); it++) {
++it

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.cc:181: it != audio_buffers_.end(); it++) {
++it

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
File chrome/browser/speech/audio_encoder.h (right):

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.h:11: namespace speech_input {
I think Brett sent an email a short time ago, you may want to do a rename to
speech rather than speech_input as it needs to match the directory name (or
conversely, rename the directory). not this change anyway.

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.h:19: SPEEX
add ","

afaict, normally enums values would also have a prefix:
  CODEC_FLAC, 
  CODEC_SPEEX,

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.h:43: AudioBufferQueue audio_buffers_;
I think all data members should be private, with protected accessors where
needed.

also, make a protected empty ctor and use a DISALLOW_COPY_AND_ASSIGN

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.h:46: }
  // namespace speech_input

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/speech_re...
File chrome/browser/speech/speech_recognizer.cc (right):

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/speech_re...
chrome/browser/speech/speech_recognizer.cc:13: #include
"third_party/flac/flac.h"
no longer needed?

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/speech_re...
chrome/browser/speech/speech_recognizer.cc:22: "audio/x-speex-with-header-byte;
rate=16000";
it'd be nice to move these to the new encoder interface

[Satish, 2011-01-17 14:02:05]

Thanks for the quick review, all comments addressed. Will submit shortly.

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
File chrome/browser/speech/audio_encoder.h (right):

http://codereview.chromium.org/6111009/diff/1/chrome/browser/speech/audio_enc...
chrome/browser/speech/audio_encoder.h:11: namespace speech_input {
On 2011/01/12 16:27:07, bulach wrote:
> I think Brett sent an email a short time ago, you may want to do a rename to
> speech rather than speech_input as it needs to match the directory name (or
> conversely, rename the directory). not this change anyway.

Yes will change to 'speech' in a subsequent CL