Return fixed hardware buffer size for odd sample rates.

media/audio/audio_util.cc

 // Copyright (c) 2012 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.
 
 // Software adjust volume of samples, allows each audio stream its own
 // volume without impacting master volume for chrome and other applications.
 
 // Implemented as templates to allow 8, 16 and 32 bit implementations.
 // 8 bit is unsigned and biased by 128.
 
@@ skipping 14 matching lines @@
 
 #if defined(OS_MACOSX)
 #include "media/audio/mac/audio_low_latency_input_mac.h"
 #include "media/audio/mac/audio_low_latency_output_mac.h"
 #elif defined(OS_WIN)
 #include "base/command_line.h"
 #include "base/win/windows_version.h"
 #include "media/audio/audio_manager_base.h"
 #include "media/audio/win/audio_low_latency_input_win.h"
 #include "media/audio/win/audio_low_latency_output_win.h"
+#include "media/base/limits.h"
 #include "media/base/media_switches.h"
 #endif
 
 namespace media {
 
 // TODO(fbarchard): Convert to intrinsics for better efficiency.
 template<class Fixed>
 static int ScaleChannel(int channel, int volume) {
   return static_cast<int>((static_cast<Fixed>(channel) * volume) >> 16);
 }
@@ skipping 253 matching lines @@
   // The sizes here were determined by experimentation and are roughly
   // the lowest value (for low latency) that still allowed glitch-free
   // audio under high loads.
   //
   // For Mac OS X and Windows the chromium audio backend uses a low-latency
   // Core Audio API, so a low buffer size is possible. For Linux, further
   // tuning may be needed.
 #if defined(OS_MACOSX)
   return 128;
 #elif defined(OS_WIN)
+  // Buffer size to use when a proper size can't be determined from the system.
+  static const int kFallbackBufferSize = 2048;
+
   if (!IsWASAPISupported()) {
     // Fall back to Windows Wave implementation on Windows XP or lower
     // and assume 48kHz as default sample rate.
-    return 2048;
+    return kFallbackBufferSize;
   }
 
   // TODO(crogers): tune this size to best possible WebAudio performance.
   // WebRTC always uses 10ms for Windows and does not call this method.
   // Note that exclusive mode is experimental.
   const CommandLine* cmd_line = CommandLine::ForCurrentProcess();
   if (cmd_line->HasSwitch(switches::kEnableExclusiveAudio)) {
     return 256;
   }
 
   // This call must be done on a COM thread configured as MTA.
   // TODO(tommi): http://code.google.com/p/chromium/issues/detail?id=103835.
   int mixing_sample_rate =
       WASAPIAudioOutputStream::HardwareSampleRate(eConsole);
 
+  // Windows will return a sample rate of 0 when no audio output is available,
+  // but we should never return a buffer size of zero.
+  if (mixing_sample_rate == 0)
+    return kFallbackBufferSize;
+
   // Use different buffer sizes depening on the sample rate . The existing
   // WASAPI implementation is tuned to provide the most stable callback
   // sequence using these combinations.
   if (mixing_sample_rate % 11025 == 0)
     // Use buffer size of ~10.15873 ms.
     return (112 * (mixing_sample_rate / 11025));
 
   if (mixing_sample_rate % 8000 == 0)
     // Use buffer size of 10ms.
     return (80 * (mixing_sample_rate / 8000));
 
+  // Ensure we always return a buffer size which is somewhat appropriate.
   LOG(ERROR) << "Unknown sample rate " << mixing_sample_rate << " detected.";
-  return (mixing_sample_rate / 100);
+  if (mixing_sample_rate > limits::kMinSampleRate)
+    return (mixing_sample_rate / 100);
+  return kFallbackBufferSize;

[Ami GONE FROM CHROMIUM, 2012/09/25 18:25:46]

any reason you're going to 2048 here from the 960 it was before the previous
change?

[DaleCurtis, 2012/09/25 18:39:30]

Most cases are now handled by the mixing_sample_rate / 100, in cases where we've
got a crazy sample rate < 8kHz, I think a larger buffer size is more prudent.

Although it doesn't really matter since the fallback code is going to say hell
no when it tries to verify the configuration and choose a high latency
appropriate buffer size via another algorithm.

 #else
   return 2048;

[Ami GONE FROM CHROMIUM, 2012/09/25 18:25:46]

constify

[DaleCurtis, 2012/09/25 18:39:30]

I intentionally skipped this because it's not in the #OS_WIN section but rather
the default buffer size for Linux, i.e. not a fallback buffer size :)

 #endif
 }
 
 ChannelLayout GetAudioInputHardwareChannelLayout(const std::string& device_id) {
   // TODO(henrika): add support for device selection on all platforms.
   // Only exists on Windows today.
 #if defined(OS_MACOSX)
   return CHANNEL_LAYOUT_MONO;
 #elif defined(OS_WIN)
   if (!IsWASAPISupported()) {
@@ skipping 54 matching lines @@
   //    out performance was degraded compared to XP.
   //  - The regression was fixed in Windows 7 and most configurations will work
   //    with 2, but some (e.g., some Sound Blasters) still need 3.
   //  - Some XP configurations (even multi-processor ones) also need 3.
   return (base::win::GetVersion() == base::win::VERSION_VISTA) ? 4 : 3;
 }
 
 #endif
 
 }  // namespace media