PulseAudio Sound Playback on Linux

media/audio/linux/pulse_output.h

+// Copyright (c) 2011 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.
+
+#ifndef MEDIA_AUDIO_LINUX_PULSE_OUTPUT_H_
+#define MEDIA_AUDIO_LINUX_PULSE_OUTPUT_H_
+
+#include <pulse/pulseaudio.h>
+
+#include <string>
+
+#include "base/message_loop.h"
+#include "base/memory/scoped_ptr.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_parameters.h"
+
+namespace media {
+class SeekableBuffer;
+}
+
+class AudioManagerLinux;
+
+class PulseAudioOutputStream : public AudioOutputStream {

[vrk (LEFT CHROMIUM), 2011/08/12 23:16:51]

Comment on what this class does.

Things to include:
 - threading (basically, you assume all AudioOutputStream methods will be called
on same thread that created this object)
 - BIG WARNING saying that this implementation blocks the audio thread to wait
for PulseAudio callbacks. (It's just one Write callback instead of all
callbacks, but still something that is worth warning about.)
 - Comment that you must Close() before delete

[slock, 2011/08/15 20:35:06]

Done.

+ public:
+  PulseAudioOutputStream(const AudioParameters& params,
+                         AudioManagerLinux* manager,
+                         MessageLoop* message_loop);
+
+  virtual ~PulseAudioOutputStream();
+
+  // Implementation of AudioOutputStream.
+  virtual bool Open();
+  virtual void Close();
+  virtual void Start(AudioSourceCallback* callback);
+  virtual void Stop();
+  virtual void SetVolume(double volume);
+  virtual void GetVolume(double* volume);
+
+ private:
+  // PulseAudio mainloop iteration loop task function; used to avoid blocking
+  // the audio thread.
+  void MainloopIterateTask();
+
+  // PulseAudio Callbacks.
+  static void ContextStateCallback(pa_context* context, void* userdata);
+  static void WriteCallback(pa_stream* stream, size_t length, void* userdata);
+
+  // Function to get another packet from the data source and write it into the
+  // client buffer.
+  void BufferPacketInClient();
+
+  // API for Proxying calls to the AudioSourceCallback provided during Start().
+  uint32 RunDataCallback(uint8* dest, uint32 max_size,
+                         AudioBuffersState buffers_state);
+
+  // Configuration constants from the constructor.  Referencable by all threads
+  // since they are constants.
+  const ChannelLayout channel_layout_;
+  const pa_sample_format_t sample_format_;
+  const uint32 sample_rate_;
+  const uint32 bytes_per_frame_;
+
+  // Device configuration data.  Populated after OpenTask() completes.
+  uint32 packet_size_;
+  uint32 frames_per_packet_;
+
+  // Flag indicating the code should stop reading from the data source or
+  // writing to the PulseAudio server.  This is set because the device has
+  // entered an unrecoverable error state, or the Close() has executed.
+  bool stream_stopped_;
+
+  // Audio manager that created us.  Used to report that we've closed.
+  AudioManagerLinux* manager_;
+
+  // PulseAudio API structs.
+  pa_context* pa_context_;
+  pa_mainloop* pa_mainloop_;
+  pa_mainloop_api* pa_mainloop_api_; // Owned by pa_mainloop_.
+
+  // PulseAudio attribute and specification structs.
+  pa_sample_spec pa_sample_specs_;
+  pa_buffer_attr pa_buffer_attributes_;
+
+  // Handle to the actual PulseAudio playback stream.
+  pa_stream* playback_handle_;
+
+  // Whether or not PulseAudio has called the WriteCallback for the most recent
+  // set of pa_mainloop iterations.
+  bool pa_write_has_calledback_;
+
+  // Internal buffer.
+  scoped_ptr<media::SeekableBuffer> client_buffer_;
+  bool source_exhausted_;

[vrk (LEFT CHROMIUM), 2011/08/12 23:16:51]

nit: comment this field and ones below (don't forget to mention ownership on
pointers)

[slock, 2011/08/15 20:35:06]

Done.

+
+  float volume_;
+
+  AudioSourceCallback* source_callback_;
+
+  MessageLoop* message_loop_;
+
+  ScopedRunnableMethodFactory<PulseAudioOutputStream> method_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(PulseAudioOutputStream);
+};
+
+#endif  // MEDIA_AUDIO_LINUX_PULSE_OUTPUT_H_