Classify ARM Chromebooks as high latency audio.

ppapi/shared_impl/ppb_audio_config_shared.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.
 
+#include "build/build_config.h"
 #include "ppapi/shared_impl/ppb_audio_config_shared.h"
 #include "ppapi/thunk/enter.h"
 #include "ppapi/thunk/ppb_instance_api.h"
 
 namespace ppapi {
 
 // Rounds up requested_size to the nearest multiple of minimum_size.
 static uint32_t CalculateMultipleOfSampleFrameCount(uint32_t minimum_size,
                                                     uint32_t requested_size) {
   const uint32_t multiple = (requested_size + minimum_size - 1) / minimum_size;
@@ skipping 59 matching lines @@
   // output stream on the browser side, so we can use whatever sample count the
   // client wants.
   if (!hardware_sample_frame_count || !hardware_sample_rate)
     return sample_frame_count;
 
   // Note: All the values below were determined through experimentation to
   // minimize jitter and back-to-back callbacks from the browser.  Please take
   // care when modifying these values as they impact a large number of users.
   // TODO(dalecurtis): Land jitter test and add documentation for updating this.
 
-  // If client is using same sample rate as audio hardware, then recommend a
-  // multiple of the audio hardware's sample frame count.
-  if (hardware_sample_rate == sample_rate) {
-    return CalculateMultipleOfSampleFrameCount(
-        hardware_sample_frame_count, sample_frame_count);
-  }
-
   // Should track the value reported by XP and ALSA backends.
   const uint32_t kHighLatencySampleFrameCount = 2048;
+#if defined(OS_CHROMEOS) && defined(ARCH_CPU_ARM_FAMILY)
+  // TODO(ihf): Remove this once ARM Chromebooks support low latency audio. For
+  // now we classify them as high latency. See crbug.com/289770. Note that
+  // Adobe Flash is affected but not HTML5, WebRTC and WebAudio (they are using
+  // real time threads).
+const bool kHighLatencyDevice = true;

[DaleCurtis, 2013/09/16 16:27:46]

indent is wrong.

[ilja, 2013/09/16 19:15:33]

Done.

+#else
+const bool kHighLatencyDevice = false;
+#endif
 
   // If the hardware requires a high latency buffer or we're at a low sample
   // rate w/ a buffer that's larger than 10ms, choose the nearest multiple of
   // the high latency sample frame count.  An example of too low and too large
   // is 16kHz and a sample frame count greater than 160 frames.
-  if (hardware_sample_frame_count >= kHighLatencySampleFrameCount ||
+  if (kHighLatencyDevice ||
+      hardware_sample_frame_count >= kHighLatencySampleFrameCount ||
       (hardware_sample_rate < 44100 &&
        hardware_sample_frame_count > hardware_sample_rate / 100u)) {
     return CalculateMultipleOfSampleFrameCount(
         sample_frame_count,
         std::max(kHighLatencySampleFrameCount, hardware_sample_frame_count));
   }
 
+  // If client is using same sample rate as audio hardware, then recommend a

[DaleCurtis, 2013/09/16 16:27:46]

This will result in a larger than necessary buffer size for clients with hw_rate
< 44.1kHz.  There aren't a lot of those and things will still work fine in the
Flash case, but its possible (future, currently non-existent) PPAPI clients may
see higher latency.

[ilja, 2013/09/16 19:15:33]

Thanks for clarifying!

+  // multiple of the audio hardware's sample frame count.
+  if (hardware_sample_rate == sample_rate) {
+    return CalculateMultipleOfSampleFrameCount(
+        hardware_sample_frame_count, sample_frame_count);
+  }
+
   // All low latency clients should be able to handle a 512 frame buffer with
   // resampling from 44.1kHz and 48kHz to higher sample rates.
   // TODO(dalecurtis): We may need to investigate making the callback thread
   // high priority to handle buffers at the absolute minimum w/o glitching.
   const uint32_t kLowLatencySampleFrameCount = 512;
 
   // Special case for 48kHz -> 44.1kHz and buffer sizes greater than 10ms.  In
   // testing most buffer sizes > 10ms led to glitching, so we choose a size we
   // know won't cause jitter.
   int min_sample_frame_count = kLowLatencySampleFrameCount;
@@ skipping 45 matching lines @@
   if (sample_frame_count > PP_AUDIOMAXSAMPLEFRAMECOUNT ||
       sample_frame_count < PP_AUDIOMINSAMPLEFRAMECOUNT)
     return false;
 
   sample_rate_ = sample_rate;
   sample_frame_count_ = sample_frame_count;
   return true;
 }
 
 }  // namespace ppapi