view base/AudioPlaySource.h @ 490:c3fb8258e34d

* Make it possible to import an entire session from an RDF document.
  However, at the moment the timings of events appear to be constrained
  by how far the audio decoder has got through its audio file at the
  time the event is queried -- need to investigate.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    This file copyright 2006 Chris Cannam.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#ifndef _AUDIO_PLAY_SOURCE_H_
#define _AUDIO_PLAY_SOURCE_H_

struct Auditionable {
    virtual ~Auditionable() { }
};

/**
 * Simple interface for audio playback.  This should be all that the
 * ViewManager needs to know about to synchronise with playback by
 * sample frame, but it doesn't provide enough to determine what is
 * actually being played or how.  See the audioio directory for a
 * concrete subclass.
 */

class AudioPlaySource
{
public:
    virtual ~AudioPlaySource() { }

    /**
     * Start playing from the given frame.  If playback is already
     * under way, reseek to the given frame and continue.
     */
    virtual void play(size_t startFrame) = 0;

    /**
     * Stop playback.
     */
    virtual void stop() = 0;

    /**
     * Return whether playback is currently supposed to be happening.
     */
    virtual bool isPlaying() const = 0;

    /**
     * Return the frame number that is currently expected to be coming
     * out of the speakers.  (i.e. compensating for playback latency.)
     */
    virtual size_t getCurrentPlayingFrame() = 0;

    /**
     * Return the current (or thereabouts) output levels in the range
     * 0.0 -> 1.0, for metering purposes.
     */
    virtual bool getOutputLevels(float &left, float &right) = 0;

    /**
     * Return the sample rate of the source material -- any material
     * that wants to play at a different rate will sound wrong.
     */
    virtual size_t getSourceSampleRate() const = 0;

    /**
     * Return the sample rate set by the target audio device (or the
     * source sample rate if the target hasn't set one).  If the
     * source and target sample rates differ, resampling will occur.
     */
    virtual size_t getTargetSampleRate() const = 0;

    /**
     * Get the block size of the target audio device.  This may be an
     * estimate or upper bound, if the target has a variable block
     * size; the source should behave itself even if this value turns
     * out to be inaccurate.
     */
    virtual size_t getTargetBlockSize() const = 0;

    /**
     * Get the number of channels of audio that will be provided
     * to the play target.  This may be more than the source channel
     * count: for example, a mono source will provide 2 channels
     * after pan.
     */
    virtual size_t getTargetChannelCount() const = 0;

    /**
     * Set a plugin or other subclass of Auditionable as an
     * auditioning effect.
     */
    virtual void setAuditioningEffect(Auditionable *) = 0;

};

#endif