Add API to query for the audio buffer size.

This is essentially identical to the GetAudioHardwareSampleRate API, except
we get the "optimal" hardware buffer size to be used.

BUG=None
TEST=None


Review URL: http://codereview.chromium.org/7837030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@101249 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 22 insertions, 0 deletions

diff --git a/media/audio/audio_util.cc b/media/audio/audio_util.cc
index 2b790d8..120e2ed 100644
--- a/media/audio/audio_util.cc
+++ b/media/audio/audio_util.cc
@@ -242,6 +242,23 @@ double GetAudioHardwareSampleRate()
 #endif
 }
 
+size_t GetAudioHardwareBufferSize() {
+  // The sizes here were determined by experimentation and are roughly
+  // the lowest value (for low latency) that still allowed glitch-free
+  // audio under high loads.
+  //
+  // For Mac OS X the chromium audio backend uses a low-latency
+  // CoreAudio API, so a low buffer size is possible.  For other OSes,
+  // further tuning may be needed.
+#if defined(OS_MACOSX)
+  return 128;
+#elif defined(OS_LINUX)
+  return 2048;
+#else
+  return 2048;
+#endif
+}
+
 // When transferring data in the shared memory, first word is size of data
 // in bytes. Actual data starts immediately after it.
 
diff --git a/media/audio/audio_util.h b/media/audio/audio_util.h
index e9452b2..6ea697b 100644
--- a/media/audio/audio_util.h
+++ b/media/audio/audio_util.h
@@ -82,6 +82,11 @@ MEDIA_EXPORT void InterleaveFloatToInt16(const std::vector<float*>& source,
 // Returns the default audio hardware sample-rate.
 MEDIA_EXPORT double GetAudioHardwareSampleRate();
 
+// Returns the optimal low-latency buffer size for the audio hardware.
+// This is the smallest buffer size the system can comfortably render
+// at without glitches.  The buffer size is in sample-frames.
+MEDIA_EXPORT size_t GetAudioHardwareBufferSize();
+
 // Functions that handle data buffer passed between processes in the shared
 // memory. Called on both IPC sides.