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..efebf9a7540d586a22f4389c4c89817fd38041e4 100644
--- a/media/audio/win/audio_low_latency_output_win.h
+++ b/media/audio/win/audio_low_latency_output_win.h
@@ -72,6 +72,21 @@
 //   supported format (X) and the new default device - to which we would like
 //   to switch - uses another format (Y), which is not supported given the
 //   configured audio parameters.
+// - The audio device is always opened with the same number of channels as
+//   it supports natively (see HardwareChannelCount()). Channel up-mixing will
+//   take place if the |params| parameter in the constructor contains a lower
+//   number of channels than the number of native channels. As an example: if
+//   the clients provides a channel count of 2 and a 7.1 headset is detected,
+//   then 2 -> 7.1 up-mixing will take place for each OnMoreData() callback.
+// - Channel down-mixing is currently not supported. It is possible to create
+//   an instance for this case but calls to Open() will fail.
+// - Support for 8-bit audio has not yet been verified and tested.
+// - Open() will fail if channel up-mixing is done for 8-bit audio.
+// - Supported channel up-mixing cases (client config -> endpoint config):
+//    o 1 -> 2
+//    o 1 -> 7.1
+//    o 2 -> 5.1
+//    o 2 -> 7.1
 //
 // Core Audio API details:
 //
@@ -115,7 +130,7 @@
 // Experimental exclusive mode:
 //
 // - It is possible to open up a stream in exclusive mode by using the
-//   --enable-exclusive-mode command line flag.
+//   --enable-exclusive-audio command line flag.
 // - The internal buffering scheme is less flexible for exclusive streams.
 //   Hence, some manual tuning will be required before deciding what frame
 //   size to use. See the WinAudioOutputTest unit test for more details.
@@ -143,6 +158,7 @@
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/simple_thread.h"
 #include "base/win/scoped_co_mem.h"
@@ -182,9 +198,19 @@ 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
@@ -194,6 +220,8 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   bool started() const { return started_; }
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(WASAPIAudioOutputStreamTest, HardwareChannelCount);
+
   // Implementation of IUnknown (trivial in this case). See
   // msdn.microsoft.com/en-us/library/windows/desktop/dd371403(v=vs.85).aspx
   // for details regarding why proper implementations of AddRef(), Release()
@@ -255,7 +283,15 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   // new default audio device.
   bool RestartRenderingUsingNewDefaultDevice();
 
-  AUDCLNT_SHAREMODE share_mode() const { return share_mode_; }
+  // Returns the number of channels the audio engine uses for its internal
+  // processing/mixing of shared-mode streams for the default endpoint device.
+  int endpoint_channel_count() { return format_.Format.nChannels; }
+
+  // The ratio between the the number of native audio channels used by the
+  // audio device and the number of audio channels from the client.
+  int channel_factor() const {
+    return (format_.Format.nChannels / client_channel_count_);

[scherkus (not reviewing), 2012/08/03 21:20:55]

OOC and something we can TODO for now, but do we always want integer truncation?

if nChannels (which is HardwareChannelCount()) is 3 (2.1) and
client_channel_count_ is 2, we end up with 1 and don't hit the up-mixing path 

will we do the right thing in that scenario? (only output to L+R channels?)

[henrika (OOO until Aug 14), 2012/08/04 16:42:23]

We only support the mixing modes listed in the "Overview of operation and
performance:" section. Your example will fail since it will not be detected as a
mixing case. If I changed to float, we would detect it but no support exists for
it in the mixing phase. Both these cases are bad and just removing int will not
be the optimal solution.

Given that I don't have access to hardware right now, I don't  dare to change
these parts. Will add a TODO and improve when I get back.

I have better ideas on how to detect mixing mode than a plain integer. This CL
has grown from "please make my G35 headset work with Chrome" to something larger
;-)

+  }
 
   // Initializes the COM library for use by the calling thread and sets the
   // thread's concurrency model to multi-threaded.
@@ -272,12 +308,14 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   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 +354,11 @@ class MEDIA_EXPORT WASAPIAudioOutputStream
   // where AUDCLNT_SHAREMODE_SHARED is the default.
   AUDCLNT_SHAREMODE share_mode_;
 
+  // The channel count set by the client in |params| which is provided to the
+  // constructor. The client must feed the AudioSourceCallback::OnMoreData()
+  // callback with PCM-data that contains this number of channels.
+  int client_channel_count_;
+
   // Counts the number of audio frames written to the endpoint buffer.
   UINT64 num_written_frames_;