Make OS audio buffer size limits visible.

media/base/audio_latency.cc

Index: media/base/audio_latency.cc
diff --git a/media/base/audio_latency.cc b/media/base/audio_latency.cc
index 61b3724efa48cc36fc8ff7c3a545c95d7ba5bb56..477b4bfeadcf842cbbb6504a269a4b035ad8c9f6 100644
--- a/media/base/audio_latency.cc
+++ b/media/base/audio_latency.cc
@@ -9,6 +9,7 @@
 #include <algorithm>
 
 #include "base/logging.h"
+#include "base/sys_info.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 
@@ -142,4 +143,75 @@ int AudioLatency::GetExactBufferSize(base::TimeDelta duration,
   return std::max(buffer_size, hardware_buffer_size);
 }
 
+#if defined(OS_MACOSX)
+namespace {
+// Define bounds for for low-latency input and output streams.
+static const int kMinimumInputOutputBufferSize = 128;
+static const int kMaximumInputOutputBufferSize = 4096;
+
+static int GetDefaultBufferSize(bool is_input, int sample_rate) {
+  // kMinimumInputOutputBufferSize is too small for the output side because
+  // CoreAudio can get into under-run if the renderer fails delivering data
+  // to the browser within the allowed time by the OS. The workaround is to
+  // use 256 samples as the default output buffer size for sample rates
+  // smaller than 96KHz.
+  // TODO(xians): Remove this workaround after WebAudio supports user defined
+  // buffer size.  See https://github.com/WebAudio/web-audio-api/issues/348
+  // for details.
+  int buffer_size = is_input ? kMinimumInputOutputBufferSize
+                             : 2 * kMinimumInputOutputBufferSize;
+  if (sample_rate > 48000) {
+    // The default buffer size is too small for higher sample rates and may lead
+    // to glitching.  Adjust upwards by multiples of the default size.
+    if (sample_rate <= 96000)
+      buffer_size = 2 * kMinimumInputOutputBufferSize;
+    else if (sample_rate <= 192000)
+      buffer_size = 4 * kMinimumInputOutputBufferSize;
+  }
+  return buffer_size;
+}
+}  // namespace
+
+int AudioLatency::GetMinimumAudioBufferSize(int sample_rate) {
+  return GetDefaultBufferSize(false, sample_rate);
+}
+
+int AudioLatency::GetMaximumAudioBufferSize(int sample_rate) {
+  return kMaximumInputOutputBufferSize;
+}
+
+int AudioLatency::GetDefaultAudioBufferSize(bool is_input, int sample_rate) {
+  return GetDefaultBufferSize(is_input, sample_rate);
+}
+#elif defined(USE_CRAS)
+namespace {
+// Define bounds for the output buffer size.
+const int kMinimumOutputBufferSize = 512;
+const int kMaximumOutputBufferSize = 8192;
+
+static int GetMinimumOutputBufferSizePerBoard() {
+  // On faster boards we can use smaller buffer size for lower latency.
+  // On slower boards we should use larger buffer size to prevent underrun.
+  std::string board = base::SysInfo::GetLsbReleaseBoard();
+  if (board == "kevin")
+    return 768;
+  else if (board == "samus")
+    return 256;
+  return kMinimumOutputBufferSize;
+}
+}  // namespace
+
+int AudioLatency::GetMinimumAudioBufferSize(int sample_rate) {
+  return GetMinimumOutputBufferSizePerBoard();
+}
+
+int AudioLatency::GetMaximumAudioBufferSize(int sample_rate) {
+  return kMaximumOutputBufferSize;
+}
+
+int AudioLatency::GetDefaultAudioBufferSize(bool is_input, int sample_rate) {
+  return GetMinimumOutputBufferSizePerBoard();
+}
+#endif
+
 }  // namespace media