Enabled mono playback support for Linux.

media/audio/linux/alsa_output.cc

 // Copyright (c) 2009 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.
 //
 // THREAD SAFETY
 //
 // The AlsaPcmOutputStream object's internal state is accessed by two threads:
 //
 //   client thread - creates the object and calls the public APIs.
 //   message loop thread - executes all the internal tasks including querying
@@ skipping 149 matching lines @@
       bytes_per_frame_(channels_ * bits_per_sample / 8),
       stop_stream_(false),
       wrapper_(wrapper),
       playback_handle_(NULL),
       source_callback_(NULL),
       frames_per_packet_(0),
       client_thread_loop_(MessageLoop::current()),
       message_loop_(message_loop) {
 
   // Sanity check input values.
-  // TODO(ajwong): Just try what happens if we allow non 2-channel audio.
-  if (channels_ != 2) {
-    LOG(WARNING) << "Only 2-channel audio is supported right now.";
+  //
+  // TODO(scherkus): ALSA works fine if you pass in multichannel audio, however
+  // it seems to be mapped to the wrong channels.  We may have to do some
+  // channel swizzling from decoder output to ALSA's preferred multichannel
+  // format.
+  if (channels_ != 1 && channels_ != 2) {
+    LOG(WARNING) << "Only 1 and 2 channel audio is supported right now.";
     shared_data_.TransitionTo(kInError);
   }
 
   if (AudioManager::AUDIO_PCM_LINEAR != format) {
     LOG(WARNING) << "Only linear PCM supported.";
     shared_data_.TransitionTo(kInError);
   }
 
   if (pcm_format_ == SND_PCM_FORMAT_UNKNOWN) {
     LOG(WARNING) << "Unsupported bits per sample: " << bits_per_sample;
@@ skipping 414 matching lines @@
 
 float AlsaPcmOutputStream::SharedData::volume() {
   AutoLock l(lock_);
   return volume_;
 }
 
 void AlsaPcmOutputStream::SharedData::set_volume(float v) {
   AutoLock l(lock_);
   volume_ = v;
 }