Add detection for repeated audio in capturing.

content/renderer/media/media_stream_audio_processor.cc

Index: content/renderer/media/media_stream_audio_processor.cc
diff --git a/content/renderer/media/media_stream_audio_processor.cc b/content/renderer/media/media_stream_audio_processor.cc
index e15e13b143c5b6e4faf5f09f43b8fcfe2fe63d38..53efaeccd22d1579b734c2e457dfe92f6581aedf 100644
--- a/content/renderer/media/media_stream_audio_processor.cc
+++ b/content/renderer/media/media_stream_audio_processor.cc
@@ -245,6 +245,7 @@ MediaStreamAudioProcessor::MediaStreamAudioProcessor(
     const MediaStreamDevice::AudioDeviceParameters& input_params,
     WebRtcPlayoutDataSource* playout_data_source)
     : render_delay_ms_(0),
+      repetition_detector_(new RepetitionDetector()),
       playout_data_source_(playout_data_source),
       audio_mirroring_(false),
       typing_detected_(false),
@@ -304,6 +305,15 @@ bool MediaStreamAudioProcessor::ProcessAndConsumeData(
   if (!capture_fifo_->Consume(&process_bus, capture_delay))
     return false;
 
+  // Detect if bit-exact repetition of audio present in the captured audio.

[Henrik Grunell, 2015/09/23 10:36:41]

Nit: "Detect bit-exact repetition of audio."

[minyue, 2015/09/25 14:40:06]

Done.

+  // We detect only one channel.
+  if (repetition_detector_) {
+    repetition_detector_->Detect(process_bus->bus()->channel(0),

[Henrik Grunell, 2015/09/23 06:54:15]

How much complexity does this add? Would be good to document that in the bug if
it isn't already.

How does the detector handle expected repetitions, like hooking a file or
generate a sinus directly to the input? (Will that be bit exact?)

[minyue, 2015/09/23 08:48:07]

It is O(n), n for number of samples. Each sample compares with the samples
sitting at the look back positions of the registered repetition patterns.

+                                 process_bus->bus()->frames(),
+                                 1,  // number of channels
+                                 input_format_.sample_rate());

[Henrik Grunell, 2015/09/23 06:54:15]

Does the |process_bus| contain the sample rate?

[minyue, 2015/09/23 08:48:07]

Unfortunately not. and that is why other places uses
input/output_format_.sample_rate() too, see, e.g.,

https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

[Henrik Grunell, 2015/09/23 10:36:41]

I looked into this more. The MediaStreamAudioBus wraps an AudioBus which
contains all information needed. Let take a an AudioBus
RepetitionDetector::Detect(const AudioBus*)
and handle it there.

[minyue, 2015/09/25 14:40:06]

It is good for me to know that AudioBus has all info. and I can remove
input_format_ here. but I am a little bit against the idea of taking AudioBus as
input to Detect(). Since the detector is written a bit more general to accept
any number of channels, and it is up to the user to decide whether to check all
channels or only one (and which one).

+  }
+
   // Use the process bus directly if audio processing is disabled.
   MediaStreamAudioBus* output_bus = process_bus;
   *new_volume = 0;