Resolves "Huge increase in audio latency on Windows following r192046"

media/audio/win/audio_manager_win.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 "media/audio/audio_io.h"
 
 #include <windows.h>
 #include <objbase.h>  // This has to be before initguid.h
 #include <initguid.h>
 #include <mmsystem.h>
@@ skipping 332 matching lines @@
     // Fall back to Windows Wave implementation on Windows XP or lower.
     DVLOG(1) << "Using WaveIn since WASAPI requires at least Vista.";
     stream = CreatePCMWaveInAudioInputStream(params, device_id);
   } else {
     stream = new WASAPIAudioInputStream(this, params, device_id);
   }
 
   return stream;
 }
 
 AudioParameters AudioManagerWin::GetPreferredOutputStreamParameters(

[DaleCurtis, 2013/04/15 18:08:57]

Ugh, not your fault, but this whole function is really hard to follow :(  Feel
free to take a stab at rewriting the whole damn thing :)

I think we should just have multiple return sections instead of trying to funnel
all the parameters down into a single return.

[henrika (OOO until Aug 14), 2013/04/15 20:28:28]

I agree, it sucks. Wonder who has written most parts of it ;-)

I can give it a try but I felt that I might as well add stuff to avoid
introducing andy mistakes.

[DaleCurtis, 2013/04/15 20:31:07]

I don't know what you're talking about!! :p  I'll take a stab at it when I have
some time.

     const AudioParameters& input_params) {
   const CommandLine* cmd_line = CommandLine::ForCurrentProcess();
   ChannelLayout channel_layout = CHANNEL_LAYOUT_STEREO;
   int sample_rate = 48000;
   int buffer_size = kFallbackBufferSize;
   int bits_per_sample = 16;
   int input_channels = 0;
   bool use_input_params = !CoreAudioUtil::IsSupported();
   if (cmd_line->HasSwitch(switches::kEnableExclusiveAudio)) {
     // TODO(crogers): tune these values for best possible WebAudio performance.
@@ skipping 19 matching lines @@
     // TODO(henrika): Figure out the right thing to do here.
     if (hw_sample_rate && hw_buffer_size) {
       sample_rate = hw_sample_rate;
       buffer_size = hw_buffer_size;
     } else {
       use_input_params = true;
     }
   }
 
   if (input_params.IsValid()) {
-    if (CoreAudioUtil::IsSupported() &&
-        CoreAudioUtil::IsChannelLayoutSupported(eRender, eConsole,
-            input_params.channel_layout())) {
-      // Open up using the same channel layout as the source if it is
-      // supported by the hardware.
-      channel_layout = input_params.channel_layout();
-      VLOG(1) << "Hardware channel layout is not used; using same "
-              << "layout as the source instead (" << channel_layout << ")";
+    if (CoreAudioUtil::IsSupported()) {
+        // Check if it is possible to open up at the specified input channel

[DaleCurtis, 2013/04/15 18:08:57]

Indent is wrong; should be 2 spaces.

[henrika (OOO until Aug 14), 2013/04/15 20:28:28]

Will fix.

[henrika (OOO until Aug 14), 2013/04/16 09:04:35]

Done.

+        // layout but avoid checking if the specified layout is the same as the
+        // hardware (preferred) layout. We do this extra check to avoid the
+        // CoreAudioUtil::IsChannelLayoutSupported() overhead in most cases.
+        if (input_params.channel_layout() != channel_layout) {

[DaleCurtis, 2013/04/15 18:08:57]

In the Exclusive mode case, channel_layout won't be set yet, so you'll end up
making an extra check here.

[henrika (OOO until Aug 14), 2013/04/15 20:28:28]

Can you elaborate. Do you want me to add a flag-check and do what if the flag is
enabled? I assume you want to always open at input layout in exclusive mode.

[DaleCurtis, 2013/04/15 20:31:07]

In the HasSwitch() block above, I'd just add a:

if (input_params.IsValid())
  channel_layout = input_params.channel_layout();

[henrika (OOO until Aug 14), 2013/04/16 09:04:35]

Done.

+          if (CoreAudioUtil::IsChannelLayoutSupported(eRender, eConsole,
+                  input_params.channel_layout())) {

[DaleCurtis, 2013/04/15 18:08:57]

Wrong indent; you can't partially wrap some of the parameters and not others. 
It's either all or nothing.

[henrika (OOO until Aug 14), 2013/04/15 20:28:28]

Will fix.

[henrika (OOO until Aug 14), 2013/04/16 09:04:35]

Done.

+            // Open up using the same channel layout as the source if it is
+            // supported by the hardware.
+            channel_layout = input_params.channel_layout();
+            VLOG(1) << "Hardware channel layout is not used; using same layout"
+                    << " as the source instead (" << channel_layout << ")";
+        }
+      }
     }
     input_channels = input_params.input_channels();
     if (use_input_params) {
       // If WASAPI isn't supported we'll fallback to WaveOut, which will take
       // care of resampling and bits per sample changes.  By setting these
       // equal to the input values, AudioOutputResampler will skip resampling
       // and bit per sample differences (since the input parameters will match
       // the output parameters).
       sample_rate = input_params.sample_rate();
       bits_per_sample = input_params.bits_per_sample();
@@ skipping 28 matching lines @@
   return new PCMWaveInAudioInputStream(this, params, kNumInputBuffers,
                                        xp_device_id);
 }
 
 /// static
 AudioManager* CreateAudioManager() {
   return new AudioManagerWin();
 }
 
 }  // namespace media