Make OS audio buffer size limits visible.

media/base/audio_latency.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/audio_latency.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 
 #include "base/logging.h"
+#include "base/sys_info.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 
 namespace media {
 
 namespace {
 #if !defined(OS_WIN)
 // Taken from "Bit Twiddling Hacks"
 // http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
 uint32_t RoundUpToPowerOfTwo(uint32_t v) {
@@ skipping 113 matching lines @@
   DCHECK_NE(0, hardware_buffer_size);
 
   // Round the requested size to the nearest multiple of the hardware size
   const int buffer_size =
       std::round(std::max(requested_buffer_size, 1.0) / hardware_buffer_size) *
       hardware_buffer_size;
 
   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