Source/WebCore/platform/audio/AudioDestination.h

/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
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 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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#ifndef AudioDestination_h
#define AudioDestination_h

#include <memory>
#include <wtf/text/WTFString.h>

namespace WebCore {

class AudioIOCallback;

// AudioDestination is an abstraction for audio hardware I/O.
// The audio hardware periodically calls the AudioIOCallback render() method asking it to render/output the next render quantum of audio.
// It optionally will pass in local/live audio input when it calls render().

class AudioDestination {
    WTF_MAKE_FAST_ALLOCATED;
public:
    // Pass in (numberOfInputChannels > 0) if live/local audio input is desired.
    // Port-specific device identification information for live/local input streams can be passed in the inputDeviceId.
    static std::unique_ptr<AudioDestination> create(AudioIOCallback&, const String& inputDeviceId, unsigned numberOfInputChannels, unsigned numberOfOutputChannels, float sampleRate);

    virtual ~AudioDestination() = default;

    virtual void start() = 0;
    virtual void stop() = 0;
    virtual bool isPlaying() = 0;

    // Sample-rate conversion may happen in AudioDestination to the hardware sample-rate
    virtual float sampleRate() const = 0;
    static float hardwareSampleRate();

    // maxChannelCount() returns the total number of output channels of the audio hardware.
    // A value of 0 indicates that the number of channels cannot be configured and
    // that only stereo (2-channel) destinations can be created.
    // The numberOfOutputChannels parameter of AudioDestination::create() is allowed to
    // be a value: 1 <= numberOfOutputChannels <= maxChannelCount(),
    // or if maxChannelCount() equals 0, then numberOfOutputChannels must be 2.
    static unsigned long maxChannelCount();
};

} // namespace WebCore

#endif // AudioDestination_h