Bug 918861 - Expose a better samplerate though the AudioStream interface. r=kinetik

--HG--
extra : rebase_source : d085d173aeb00f47f56016c0a1d1bf7fe11fb6f3

content/media/AudioStream.cpp

@@ -44,6 +44,9 @@ static uint32_t gCubebLatency;
 static bool gCubebLatencyPrefSet;
 static const uint32_t CUBEB_NORMAL_LATENCY_MS = 100;
 
+StaticMutex AudioStream::mMutex;
+uint32_t AudioStream::mPreferredSampleRate = 0;
+
 /**
  * When MOZ_DUMP_AUDIO is set in the environment (to anything),
  * we'll drop a series of files in the current working directory named
@@ -441,6 +444,23 @@ int AudioStream::MaxNumberOfChannels()
   return static_cast<int>(maxNumberOfChannels);
 }
 
+int AudioStream::PreferredSampleRate()
+{
+  StaticMutexAutoLock lock(AudioStream::mMutex);
+  // Get the preferred samplerate for this platform, or fallback to something
+  // sensible if we fail. We cache the value, because this might be accessed
+  // often, and the complexity of the function call below depends on the
+  // backend used.
+  const int fallbackSampleRate = 44100;
+  if (mPreferredSampleRate == 0) {
+    if (cubeb_get_preferred_sample_rate(GetCubebContext(), &mPreferredSampleRate) != CUBEB_OK) {
+      mPreferredSampleRate = fallbackSampleRate;
+    }
+  }
+
+  return mPreferredSampleRate;
+}
+
 static void SetUint16LE(uint8_t* aDest, uint16_t aValue)
 {
   aDest[0] = aValue & 0xFF;

content/media/AudioStream.h

@@ -11,6 +11,7 @@
 #include "nsAutoPtr.h"
 #include "nsCOMPtr.h"
 #include "Latency.h"
+#include "mozilla/StaticMutex.h"
 
 namespace soundtouch {
 class SoundTouch;
@@ -116,6 +117,10 @@ public:
   // Returns the maximum number of channels supported by the audio hardware.
   static int MaxNumberOfChannels();
 
+  // Returns the samplerate the systems prefer, because it is the
+  // samplerate the hardware/mixer supports.
+  static int PreferredSampleRate();
+
   // Initialize the audio stream. aNumChannels is the number of audio
   // channels (1 for mono, 2 for stereo, etc) and aRate is the sample rate
   // (22050Hz, 44100Hz, etc).
@@ -183,6 +188,11 @@ public:
   virtual nsresult SetPreservesPitch(bool aPreservesPitch);
 
 protected:
+  // This mutex protects the mPreferedSamplerate member below.
+  static StaticMutex mMutex;
+  // Prefered samplerate, in Hz (characteristic of the
+  // hardware/mixer/platform/API used).
+  static uint32_t mPreferredSampleRate;
   // Input rate in Hz (characteristic of the media being played)
   int mInRate;
   // Output rate in Hz (characteristic of the playback rate)