Add a unified audio I/O backend for ChromeOS.

media/audio/cras/cras_unified.h

+// Copyright 2013 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.
+//
+// Creates a unified stream based on the cras (ChromeOS audio server) interface.
+//
+// CrasUnifiedStream object is *not* thread-safe and should only be used
+// from the audio thread.
+
+#ifndef MEDIA_AUDIO_LINUX_CRAS_UNIFIED_H_
+#define MEDIA_AUDIO_LINUX_CRAS_UNIFIED_H_
+
+#include <alsa/asoundlib.h>
+#include <cras_client.h>
+
+#include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
+#include "media/audio/audio_io.h"
+
+namespace media {
+
+class AudioManagerCras;
+class AudioParameters;
+
+// Implementation of AudioOuputStream for Chrome OS using the Chrome OS audio
+// server.
+class MEDIA_EXPORT CrasUnifiedStream : public AudioOutputStream {
+ public:
+  // The ctor takes all the usual parameters, plus |manager| which is the
+  // audio manager who is creating this object.
+  CrasUnifiedStream(const AudioParameters& params, AudioManagerCras* manager);
+
+  // The dtor is typically called by the AudioManager only and it is usually
+  // triggered by calling AudioUnifiedStream::Close().
+  virtual ~CrasUnifiedStream();
+
+  // Implementation of AudioOutputStream.
+  virtual bool Open() OVERRIDE;
+  virtual void Close() OVERRIDE;
+  virtual void Start(AudioSourceCallback* callback) OVERRIDE;
+  virtual void Stop() OVERRIDE;
+  virtual void SetVolume(double volume) OVERRIDE;
+  virtual void GetVolume(double* volume) OVERRIDE;
+
+ private:
+  // Convert Latency in time to bytes.
+  unsigned int GetBytesLatency(const struct timespec& latency);
+
+  // Handles captured audio and fills the ouput with audio to be played.
+  static int UnifiedCallback(cras_client* client,
+                             cras_stream_id_t stream_id,
+                             uint8* input_samples,
+                             uint8* output_samples,
+                             unsigned int frames,
+                             const timespec* input_ts,
+                             const timespec* output_ts,
+                             void* arg);
+
+  // Handles notificaiton that there was an error with the playback stream.
+  static int StreamError(cras_client* client,
+                         cras_stream_id_t stream_id,
+                         int err,
+                         void* arg);
+
+  // Chooses the correct audio callback based on stream direction.
+  uint32 DispatchCalback(size_t frames,

[DaleCurtis, 2013/03/26 19:23:01]

Callback

+                         uint8* input_samples,
+                         uint8* output_samples,
+                         const timespec* input_ts,
+                         const timespec* output_ts);
+
+  // Receives input samples and write output samples for a unified I/O stream.
+  uint32 ReadWriteAudio(size_t frames,
+                        uint8* input_samples,
+                        uint8* output_samples,
+                        const timespec* input_ts,
+                        const timespec* output_ts);
+
+  // Writes audio for a playback stream.
+  uint32 WriteAudio(size_t frames, uint8* buffer, const timespec* sample_ts);
+
+  // Deals with an error that occured in the stream.  Called from StreamError().
+  void NotifyStreamError(int err);
+
+  // The client used to communicate with the audio server.
+  cras_client* client_;
+
+  // ID of the playing stream.
+  cras_stream_id_t stream_id_;
+
+  // Packet size in samples.
+  uint32 samples_per_packet_;
+
+  // Size of frame in bytes.
+  uint32 bytes_per_frame_;
+
+  // Rate in Hz.
+  size_t frame_rate_;
+
+  // Number of channels.
+  size_t output_channels_;
+
+  // PCM format for Alsa.
+  const snd_pcm_format_t pcm_format_;
+
+  // True if stream is playing.
+  bool is_playing_;
+
+  // Volume level from 0.0 to 1.0.
+  float volume_;
+
+  // Audio manager that created us.  Used to report that we've been closed.
+  AudioManagerCras* manager_;
+
+  // Callback to get audio samples.
+  AudioSourceCallback* source_callback_;
+
+  // Container for exchanging data with AudioSourceCallback::OnMoreIOData().
+  scoped_ptr<AudioBus> input_bus_;
+  scoped_ptr<AudioBus> output_bus_;
+
+  // Direciton of the stream.
+  CRAS_STREAM_DIRECTION stream_direction_;
+
+  DISALLOW_COPY_AND_ASSIGN(CrasUnifiedStream);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_LINUX_CRAS_UNIFIED_H_