Reland 10952007: Pass through small buffer sizes without FIFO on Linux

media/audio/linux/audio_manager_linux.cc

Index: media/audio/linux/audio_manager_linux.cc
diff --git a/media/audio/linux/audio_manager_linux.cc b/media/audio/linux/audio_manager_linux.cc
index b126ed1fdb4b3d699a05fa9bf403389f68864378..e7da9319a850627c67f96cb138c8e97ff6ae95a7 100644
--- a/media/audio/linux/audio_manager_linux.cc
+++ b/media/audio/linux/audio_manager_linux.cc
@@ -10,7 +10,9 @@
 #include "base/nix/xdg_util.h"
 #include "base/process_util.h"
 #include "base/stl_util.h"
+#include "media/audio/audio_parameters.h"
 #include "media/audio/audio_output_dispatcher.h"
+#include "media/audio/audio_util.h"
 #include "media/audio/linux/alsa_input.h"
 #include "media/audio/linux/alsa_output.h"
 #include "media/audio/linux/alsa_wrapper.h"
@@ -342,4 +344,22 @@ AudioManager* CreateAudioManager() {
   return new AudioManagerLinux();
 }
 
+AudioParameters AudioManagerLinux::GetPreferredLowLatencyOutputStreamParameters(
+    const AudioParameters& input_params) {
+  // Since Linux doesn't actually have a low latency path the hardware buffer
+  // size is quite large in order to prevent glitches with general usage.  Some
+  // clients, such as WebRTC, have a more limited use case and work acceptably
+  // with a smaller buffer size.  The check below allows clients which want to
+  // try a smaller buffer size on Linux to do so.
+  int buffer_size = std::min(
+      static_cast<size_t>(input_params.frames_per_buffer()),
+      GetAudioHardwareBufferSize());
+
+  // TODO(dalecurtis): This should include bits per channel and channel layout
+  // eventually.
+  return AudioParameters(
+      AudioParameters::AUDIO_PCM_LOW_LATENCY, input_params.channel_layout(),
+      GetAudioHardwareSampleRate(), 16, buffer_size);
+}
+
 }  // namespace media