audio_io.h | Explore in Territory

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MEDIA_AUDIO_AUDIO_IO_H_
#define MEDIA_AUDIO_AUDIO_IO_H_

#include <stdint.h>

#include "base/time/time.h"
#include "media/base/audio_bus.h"
#include "media/base/audio_glitch_info.h"
#include "media/base/media_export.h"

// Low-level audio output support. To make sound there are 3 objects involved:
// - AudioSource : produces audio samples on a pull model. Implements
//   the AudioSourceCallback interface.
// - AudioOutputStream : uses the AudioSource to render audio on a given
//   channel, format and sample frequency configuration. Data from the
//   AudioSource is delivered in a 'pull' model.
// - AudioManager : factory for the AudioOutputStream objects, manager
//   of the hardware resources and mixer control.
//
// The number and configuration of AudioOutputStream does not need to match the
// physically available hardware resources. For example you can have:
//
//  MonoPCMSource1 --> MonoPCMStream1 --> |       | --> audio left channel
//  StereoPCMSource -> StereoPCMStream -> | mixer |
//  MonoPCMSource2 --> MonoPCMStream2 --> |       | --> audio right channel
//
// This facility's objective is mix and render audio with low overhead using
// the OS basic audio support, abstracting as much as possible the
// idiosyncrasies of each platform. Non-goals:
// - Positional, 3d audio
// - Dependence on non-default libraries such as DirectX 9, 10, XAudio
// - Digital signal processing or effects
// - Extra features if a specific hardware is installed (EAX, X-fi)
//
// The primary client of this facility is audio coming from several tabs.
// Specifically for this case we avoid supporting complex formats such as MP3
// or WMA. Complex format decoding should be done by the renderers.

// Models an audio stream that gets rendered to the audio hardware output.
// Because we support more audio streams than physically available channels
// a given AudioOutputStream might or might not talk directly to hardware.
// An audio stream allocates several buffers for audio data and calls
// AudioSourceCallback::OnMoreData() periodically to fill these buffers,
// as the data is written to the audio device. Size of each packet is determined
// by |samples_per_packet| specified in AudioParameters  when the stream is
// created.

namespace media {

class MEDIA_EXPORT AudioOutputStream { … };

// Models an audio sink receiving recorded audio from the audio driver.
class MEDIA_EXPORT AudioInputStream { … };

}  // namespace media

#endif  // MEDIA_AUDIO_AUDIO_IO_H_
chromium/media/audio/audio_io.h
