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 67a5d6c5f0a2c496c6e8828815110ac06f3ad202..c19177897bd5e8bfdc554a2d5a3820ece280e66e 100644 |
--- a/media/audio/win/audio_low_latency_output_win.h |
+++ b/media/audio/win/audio_low_latency_output_win.h |
@@ -112,6 +112,30 @@ |
// - All callback methods from the IMMNotificationClient interface will be |
// called on a Windows-internal MMDevice thread. |
// |
+// Experimental exclusive mode (DO NOT USE IN PRODUCTION CODE): |
+// |
+// - It is possible to open up a stream in exclusive mode by using the |
+// |share_mode| flag in the constructor. To try it out, set this flag to |
+// AUDCLNT_SHAREMODE_EXCLUSIVE. |
+// - The internal buffering scheme is less flexible for exclusive-mode streams. |
+// Hence, some manual tuning will be required before deciding what frame |
+// size to use. See the WinAudioOutputTest unit test for more details. |
+// - If an application opens a stream in exclusive mode, the application has |
+// exclusive use of the audio endpoint device that plays the stream. |
+// - Exclusive-mode access to an audio device can block crucial system sounds, |
+// prevent interoperability with other applications, and otherwise degrade |
+// the user experience. |
+// - Exclusive-mode should only be utilized when the lowest possible latency |
+// is important. |
+// - In exclusive mode, the client can choose to open the stream in any audio |
+// format that the endpoint device supports. |
+// - Initial measurements on Windows 7 have shown that the lowest possible |
+// latencies we can achieve are: |
+// o ~3.3333ms @ 48kHz <=> 160 audio frames per buffer. |
+// o ~3.6281ms @ 44.1kHz <=> 160 audio frames per buffer. |
+// - See msdn.microsoft.com/en-us/library/windows/desktop/dd370844(v=vs.85).aspx |
+// for more details. |
+ |
#ifndef MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_OUTPUT_WIN_H_ |
#define MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_OUTPUT_WIN_H_ |
@@ -146,9 +170,13 @@ class MEDIA_EXPORT WASAPIAudioOutputStream |
public: |
// The ctor takes all the usual parameters, plus |manager| which is the |
// the audio manager who is creating this object. |
+ // Note that, |share_mode| shall be set to AUDCLNT_SHAREMODE_SHARED in |
+ // production code. AUDCLNT_SHAREMODE_EXCLUSIVE is also supported but must |
+ // only be used behind a command-line flag. |
WASAPIAudioOutputStream(AudioManagerWin* manager, |
const AudioParameters& params, |
- ERole device_role); |
+ ERole device_role, |
+ AUDCLNT_SHAREMODE share_mode); |
// The dtor is typically called by the AudioManager only and it is usually |
// triggered by calling AudioOutputStream::Close(). |
virtual ~WASAPIAudioOutputStream(); |
@@ -163,6 +191,7 @@ class MEDIA_EXPORT WASAPIAudioOutputStream |
// 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. |
static int HardwareSampleRate(ERole device_role); |
bool started() const { return started_; } |
@@ -206,7 +235,7 @@ class MEDIA_EXPORT WASAPIAudioOutputStream |
void HandleError(HRESULT err); |
// The Open() method is divided into these sub methods. |
- HRESULT SetRenderDevice(ERole device_role); |
+ HRESULT SetRenderDevice(); |
HRESULT ActivateRenderDevice(); |
HRESULT GetAudioEngineStreamFormat(); |
bool DesiredFormatIsSupported(); |
@@ -222,6 +251,8 @@ class MEDIA_EXPORT WASAPIAudioOutputStream |
// new default audio device. |
bool RestartRenderingUsingNewDefaultDevice(); |
+ AUDCLNT_SHAREMODE share_mode() const { return share_mode_; } |
+ |
// Initializes the COM library for use by the calling thread and sets the |
// thread's concurrency model to multi-threaded. |
base::win::ScopedCOMInitializer com_init_; |
@@ -276,6 +307,13 @@ class MEDIA_EXPORT WASAPIAudioOutputStream |
// Defines the role that the system has assigned to an audio endpoint device. |
ERole device_role_; |
+ // The sharing mode for the connection. |
+ // Valid values are AUDCLNT_SHAREMODE_SHARED and AUDCLNT_SHAREMODE_EXCLUSIVE |
+ // where AUDCLNT_SHAREMODE_SHARED is the default. |
+ // This member is not modified (only read) after construction hence we don't |
+ // have to pro |
+ AUDCLNT_SHAREMODE share_mode_; |
+ |
// Counts the number of audio frames written to the endpoint buffer. |
UINT64 num_written_frames_; |