Implement audio recording for Linux via ALSA.

media/audio/linux/alsa_input.h

+// Copyright (c) 2010 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_ALSA_INPUT_H_
+#define MEDIA_AUDIO_LINUX_ALSA_INPUT_H_
+
+#include <alsa/asoundlib.h>
+
+#include <string>
+
+#include "base/scoped_ptr.h"
+#include "base/task.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_parameters.h"
+
+class AlsaWrapper;
+
+// Provides an input stream for audio capture based on the ALSA PCM interface.
+// This object is not thread safe and all methods should be invoked in the
+// thread that created the object.
+class AlsaPcmInputStream : public AudioInputStream {
+ public:
+  // Pass this to the constructor if you want to attempt auto-selection
+  // of the audio recording device.
+  static const char* kAutoSelectDevice;
+
+  // Create a PCM Output stream for the ALSA device identified by
+  // |device_name|. If unsure of what to use for |device_name|, use
+  // |kAutoSelectDevice|.
+  AlsaPcmInputStream(const std::string& device_name,
+                     const AudioParameters& params,
+                     int samples_per_packet,
+                     AlsaWrapper* wrapper);
+
+  // Implementation of AudioOutputStream.
+  virtual bool Open();
+  virtual void Start(AudioInputCallback* callback);
+  virtual void Stop();
+  virtual void Close();
+
+ private:
+  // Logs the error and invokes any registered callbacks.
+  void HandleError(const char* method, int error);
+
+  // Reads one or more packets of audio from the device, passes on to the
+  // registered callback and schedules the next read.
+  void ReadAudio();
+
+  // Recovers from any device errors if possible.
+  bool Recover(int error);
+
+  std::string device_name_;
+  AudioParameters params_;
+  int samples_per_packet_;
+  int bytes_per_packet_;
+  AlsaWrapper* wrapper_;
+  int packet_duration_ms_;  // Length of each recorded packet in milliseconds.
+  AudioInputCallback* callback_;  // Valid during a recording session.
+  base::Time next_read_time_;  // Scheduled time for the next read callback.
+  snd_pcm_t* device_handle_;  // Handle to the ALSA PCM recording device.
+  ScopedRunnableMethodFactory<AlsaPcmInputStream> task_factory_;
+  scoped_ptr<uint8> audio_packet_;  // Data buffer used for reading audio data.
+
+  DISALLOW_COPY_AND_ASSIGN(AlsaPcmInputStream);
+};
+
+#endif  // MEDIA_AUDIO_LINUX_ALSA_INPUT_H_