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// Copyright (c) 2012 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.
#include <stdint.h>
#include "base/atomic_ref_count.h"
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/threading/thread_checker.h"
#include "base/timer/timer.h"
#include "build/build_config.h"
#include "media/audio/audio_io.h"
#include "media/audio/audio_manager.h"
#include "media/audio/audio_power_monitor.h"
#include "media/audio/audio_source_diverter.h"
#include "media/audio/simple_sources.h"
#include "media/base/media_export.h"
// An AudioOutputController controls an AudioOutputStream and provides data
// to this output stream. It has an important function that it executes
// audio operations like play, pause, stop, etc. on a separate thread,
// namely the audio manager thread.
// All the public methods of AudioOutputController are non-blocking.
// The actual operations are performed on the audio manager thread.
// Here is a state transition diagram for the AudioOutputController:
// *[ Empty ] --> [ Created ] --> [ Playing ] -------.
// | | | ^ |
// | | | | |
// | | | | v
// | | | `----- [ Paused ]
// | | | |
// | v v |
// `-----------> [ Closed ] <-----------'
// * Initial state
// At any time after reaching the Created state but before Closed, the
// AudioOutputController may be notified of a device change via
// OnDeviceChange(). As the OnDeviceChange() is processed, state transitions
// will occur, ultimately ending up in an equivalent pre-call state. E.g., if
// the state was Paused, the new state will be Created, since these states are
// all functionally equivalent and require a Play() call to continue to the next
// state.
// The AudioOutputStream can request data from the AudioOutputController via the
// AudioSourceCallback interface. AudioOutputController uses the SyncReader
// passed to it via construction to synchronously fulfill this read request.
namespace media {
class MEDIA_EXPORT AudioOutputController
: public base::RefCountedThreadSafe<AudioOutputController>,
public AudioOutputStream::AudioSourceCallback,
public AudioSourceDiverter,
NON_EXPORTED_BASE(public AudioManager::AudioDeviceListener) {
// An event handler that receives events from the AudioOutputController. The
// following methods are called on the audio manager thread.
class MEDIA_EXPORT EventHandler {
virtual void OnCreated() = 0;
virtual void OnPlaying() = 0;
virtual void OnPaused() = 0;
virtual void OnError() = 0;
virtual ~EventHandler() {}
// A synchronous reader interface used by AudioOutputController for
// synchronous reading.
// TODO(crogers): find a better name for this class and the Read() method
// now that it can handle synchronized I/O.
class SyncReader {
virtual ~SyncReader() {}
// Notify the synchronous reader the number of bytes in the
// AudioOutputController not yet played. This is used by SyncReader to
// prepare more data and perform synchronization. Also inform about if any
// frames has been skipped by the renderer (typically the OS). The renderer
// source can handle this appropriately depending on the type of source. An
// ordinary file playout would ignore this.
virtual void UpdatePendingBytes(uint32_t bytes,
uint32_t frames_skipped) = 0;
// Attempts to completely fill |dest|, zeroing |dest| if the request can not
// be fulfilled (due to timeout).
virtual void Read(AudioBus* dest) = 0;
// Close this synchronous reader.
virtual void Close() = 0;
// Factory method for creating an AudioOutputController.
// This also creates and opens an AudioOutputStream on the audio manager
// thread, and if this is successful, the |event_handler| will receive an
// OnCreated() call from the same audio manager thread. |audio_manager| must
// outlive AudioOutputController.
// The |output_device_id| can be either empty (default device) or specify a
// specific hardware device for audio output.
static scoped_refptr<AudioOutputController> Create(
AudioManager* audio_manager, EventHandler* event_handler,
const AudioParameters& params, const std::string& output_device_id,
SyncReader* sync_reader);
// Indicates whether audio power level analysis will be performed. If false,
// ReadCurrentPowerAndClip() can not be called.
static bool will_monitor_audio_levels() {
#if defined(OS_ANDROID) || defined(OS_IOS)
return false;
return true;
// Methods to control playback of the stream.
// Starts the playback of this audio output stream.
void Play();
// Pause this audio output stream.
void Pause();
// Closes the audio output stream. The state is changed and the resources
// are freed on the audio manager thread. closed_task is executed after that.
// Callbacks (EventHandler and SyncReader) must exist until closed_task is
// called.
// It is safe to call this method more than once. Calls after the first one
// will have no effect.
void Close(const base::Closure& closed_task);
// Sets the volume of the audio output stream.
void SetVolume(double volume);
// Calls |callback| (on the caller's thread) with the current output
// device ID.
void GetOutputDeviceId(
base::Callback<void(const std::string&)> callback) const;
// Changes which output device to use. If desired, you can provide a
// callback that will be notified (on the thread you called from)
// when the function has completed execution.
// Changing the output device causes the controller to go through
// the same state transition back to the current state as a call to
// OnDeviceChange (unless it is currently diverting, see
// Start/StopDiverting below, in which case the state transition
// will happen when StopDiverting is called).
void SwitchOutputDevice(const std::string& output_device_id,
const base::Closure& callback);
// AudioSourceCallback implementation.
int OnMoreData(AudioBus* dest,
uint32_t total_bytes_delay,
uint32_t frames_skipped) override;
void OnError(AudioOutputStream* stream) override;
// AudioDeviceListener implementation. When called AudioOutputController will
// shutdown the existing |stream_|, transition to the kRecreating state,
// create a new stream, and then transition back to an equivalent state prior
// to being called.
void OnDeviceChange() override;
// AudioSourceDiverter implementation.
const AudioParameters& GetAudioParameters() override;
void StartDiverting(AudioOutputStream* to_stream) override;
void StopDiverting() override;
// Accessor for AudioPowerMonitor::ReadCurrentPowerAndClip(). See comments in
// audio_power_monitor.h for usage. This may be called on any thread.
std::pair<float, bool> ReadCurrentPowerAndClip();
// Internal state of the source.
enum State {
// Time constant for AudioPowerMonitor. See AudioPowerMonitor ctor comments
// for semantics. This value was arbitrarily chosen, but seems to work well.
enum { kPowerMeasurementTimeConstantMillis = 10 };
friend class base::RefCountedThreadSafe<AudioOutputController>;
~AudioOutputController() override;
AudioOutputController(AudioManager* audio_manager, EventHandler* handler,
const AudioParameters& params,
const std::string& output_device_id,
SyncReader* sync_reader);
// The following methods are executed on the audio manager thread.
void DoCreate(bool is_for_device_change);
void DoPlay();
void DoPause();
void DoClose();
void DoSetVolume(double volume);
std::string DoGetOutputDeviceId() const;
void DoSwitchOutputDevice(const std::string& output_device_id);
void DoReportError();
void DoStartDiverting(AudioOutputStream* to_stream);
void DoStopDiverting();
// Helper method that stops the physical stream.
void StopStream();
// Helper method that stops, closes, and NULLs |*stream_|.
void DoStopCloseAndClearStream();
// Checks if a stream was started successfully but never calls OnMoreData().
void WedgeCheck();
AudioManager* const audio_manager_;
const AudioParameters params_;
EventHandler* const handler_;
// Specifies the device id of the output device to open or empty for the
// default output device.
std::string output_device_id_;
AudioOutputStream* stream_;
// When non-NULL, audio is being diverted to this stream.
AudioOutputStream* diverting_to_stream_;
// The current volume of the audio stream.
double volume_;
// |state_| may only be used on the audio manager thread.
State state_;
// SyncReader is used only in low latency mode for synchronous reading.
SyncReader* const sync_reader_;
// The message loop of audio manager thread that this object runs on.
const scoped_refptr<base::SingleThreadTaskRunner> message_loop_;
// Scans audio samples from OnMoreData() as input to compute power levels.
AudioPowerMonitor power_monitor_;
// Flags when we've asked for a stream to start but it never did.
base::AtomicRefCount on_more_io_data_called_;
scoped_ptr<base::OneShotTimer> wedge_timer_;
// Flag which indicates errors received during Stop/Close should be ignored.
// These errors are generally harmless since a fresh stream is about to be
// recreated, but if forwarded, renderer side clients may consider them
// catastrophic and abort their operations.
// If |stream_| is started then |ignore_errors_during_stop_close_| must only
// be accessed while |error_lock_| is held.
bool ignore_errors_during_stop_close_;
base::Lock error_lock_;
} // namespace media