Adds support for multi-channel output audio for the low-latency path in Windows.

media/audio/win/audio_low_latency_output_win.h

Index: media/audio/win/audio_low_latency_output_win.h
diff --git a/media/audio/win/audio_low_latency_output_win.h b/media/audio/win/audio_low_latency_output_win.h
index 2c217ccf976b1e3023ad71fd68f53e3abfd57ce1..73251003e7a7239e31d1dd1da256852c47f06702 100644
--- a/media/audio/win/audio_low_latency_output_win.h
+++ b/media/audio/win/audio_low_latency_output_win.h
@@ -182,9 +182,19 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   virtual void SetVolume(double volume) OVERRIDE;
   virtual void GetVolume(double* volume) OVERRIDE;
 
-  // Retrieves the stream format that the audio engine uses for its internal
-  // processing/mixing of shared-mode streams.
-  // This method should not be used in combination with exclusive-mode streams.
+  // Retrieves the number of channels the audio engine uses for its internal
+  // processing/mixing of shared-mode streams for the default endpoint device.
+  static int HardwareChannelCount();
+
+  // Retrieves the channel layout the audio engine uses for its internal
+  // processing/mixing of shared-mode streams for the default endpoint device.
+  // Note that we convert an internal channel layout mask (see ChannelMask())
+  // into a Chrome-specific channel layout enumerator in this method, hence
+  // the match might not be perfect.
+  static ChannelLayout HardwareChannelLayout();
+
+  // Retrieves the sample rate the audio engine uses for its internal
+  // processing/mixing of shared-mode streams for the default endpoint device.
   static int HardwareSampleRate(ERole device_role);
 
   // Returns AUDCLNT_SHAREMODE_EXCLUSIVE if --enable-exclusive-mode is used
@@ -237,6 +247,10 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   bool DesiredFormatIsSupported();
   HRESULT InitializeAudioEngine();
 
+  // Retrieves the stream format that the audio engine uses for its internal
+  // processing/mixing of shared-mode streams.
+  static HRESULT GetMixFormat(ERole device_role, WAVEFORMATEX** device_format);

[scherkus (not reviewing), 2012/08/01 00:14:05]

any reason static private methods need to be here?

if they don't need to access private/protected members of this class then they
should all be moved into the .cc

sames goes w/ ChannelConfig() and ChannelConfigToChromeChannelLayout()

[henrika (OOO until Aug 14), 2012/08/01 16:11:09]

Great input, thanks. I actually did use private members here before but no
longer. Will fix.

Question: comments; do they go above the function definition or "inside" (first
line below def.)?

[scherkus (not reviewing), 2012/08/02 00:41:57]

Above the function.

+
   // Called when the device will be opened in shared mode and use the
   // internal audio engine's mix format.
   HRESULT SharedModeInitialization();
@@ -255,7 +269,32 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   // new default audio device.
   bool RestartRenderingUsingNewDefaultDevice();
 
+  // Retrieves an integer mask which corresponds to the channel layout the
+  // audio engine uses for its internal processing/mixing of shared-mode
+  // streams. This mask indicates which channels are present in the multi-
+  // channel stream. The least significant bit corresponds with the Front Left
+  // speaker, the next least significant bit corresponds to the Front Right
+  // speaker, and so on, continuing in the order defined in KsMedia.h.
+  // See http://msdn.microsoft.com/en-us/library/windows/hardware/ff537083(v=vs.85).aspx
+  // for more details.
+  static uint32 ChannelConfig();

[tommi (sloooow) - chröme, 2012/07/31 21:39:30]

Maybe we could define our own type for channel config to avoid mixing it up with
other ints.  e.g.
typedef uint32 ChannelConfig;
Down the line, we could then upgrade that typedef to a class that takes care of
all the bit manipulation code as it starts to spread.

[henrika (OOO until Aug 14), 2012/08/01 16:11:09]

Added typedef ChannelConfigMask in media. Got conflict if I used ChannelConfig
(same as ChannelConfig()).

+
+  // Converts Microsoft's channel configuration to Chrome's ChannelLayout.
+  // This mapping is not perfect but the best we can do given the current
+  // ChannelLayout enumerator and the Windows-specific speaker configurations
+  // defined in ksmedia.h. Don't assume that the channel ordering in
+  // ChannelLayout is exactly the same as the Windows specific configuration.
+  // As an example: KSAUDIO_SPEAKER_7POINT1_SURROUND is mapped to
+  // CHANNEL_LAYOUT_7_1 but the positions of Back L, Back R and Side L, Side R
+  // speakers are different in these two definitions.
+  static ChannelLayout ChannelConfigToChromeChannelLayout(uint32 layout);
+
   AUDCLNT_SHAREMODE share_mode() const { return share_mode_; }
+  int endpoint_channel_count() const { return endpoint_channel_count_; }

[scherkus (not reviewing), 2012/08/01 00:14:05]

huh? these are all private methods -- why the accessors instead of accessing the
variables directly?

also I think we can compute these values as opposed to storing additional data
-- see my notes in the .cc

[henrika (OOO until Aug 14), 2012/08/01 16:11:09]

Got it. Will clean up.

+  uint32 endpoint_channel_config() const { return endpoint_channel_config_; }
+  int client_channel_count() const { 
+    return client_audio_parameters_.channels();
+  }
 
   // Initializes the COM library for use by the calling thread and sets the
   // thread's concurrency model to multi-threaded.
@@ -267,17 +306,21 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   // Our creator, the audio manager needs to be notified when we close.
   AudioManagerWin* manager_;
 
+  AudioParameters client_audio_parameters_;

[tommi (sloooow) - chröme, 2012/07/31 21:39:30]

are there any other audio parameters that this class needs to worry about? 
(just wondering about the 'client_' qualifier)

[henrika (OOO until Aug 14), 2012/08/01 16:11:09]

I store this one to keep track of the parameters set by the user at
construction. It helps me detect if there is any difference between the #input
channels and the #native channels. Might be overkill to store the complete
class.

+
   // Rendering is driven by this thread (which has no message loop).
   // All OnMoreData() callbacks will be called from this thread.
   base::DelegateSimpleThread* render_thread_;
 
   // Contains the desired audio format which is set up at construction.
-  WAVEFORMATEX format_;
+  // Extended PCM waveform format structure based on WAVEFORMATEXTENSIBLE.
+  // Use this for multiple channel and hi-resolution PCM data.
+  WAVEFORMATPCMEX format_;
 
   // Copy of the audio format which we know the audio engine supports.
   // It is recommended to ensure that the sample rate in |format_| is identical
   // to the sample rate in |audio_engine_mix_format_|.
-  base::win::ScopedCoMem<WAVEFORMATEX> audio_engine_mix_format_;
+  base::win::ScopedCoMem<WAVEFORMATPCMEX> audio_engine_mix_format_;
 
   bool opened_;
   bool started_;
@@ -316,6 +359,18 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   // where AUDCLNT_SHAREMODE_SHARED is the default.
   AUDCLNT_SHAREMODE share_mode_;
 
+  // Contains the number of channels the audio engine uses for its internal
+  // processing/mixing of shared-mode streams for the default endpoint device.
+  const int endpoint_channel_count_;
+
+  // Contains the channel configuration the audio engine uses for its internal
+  // processing/mixing of shared-mode streams for the default endpoint
+  // device.
+  const uint32 endpoint_channel_config_;
+
+  // TODO(henrika): add comments....
+  int channel_factor_;
+
   // Counts the number of audio frames written to the endpoint buffer.
   UINT64 num_written_frames_;