root/Source/modules/webaudio/MediaElementAudioSourceNode.cpp

DEFINITIONS

1. create
2. m_sourceSampleRate
3. setFormat
4. process
5. lock
6. unlock

/*
 * Copyright (C) 2011, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 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
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "modules/webaudio/MediaElementAudioSourceNode.h"

#include "core/html/HTMLMediaElement.h"
#include "modules/webaudio/AudioContext.h"
#include "modules/webaudio/AudioNodeOutput.h"
#include "platform/Logging.h"
#include "platform/graphics/media/MediaPlayer.h"
#include "wtf/Locker.h"

// These are somewhat arbitrary limits, but we need to do some kind of sanity-checking.
const unsigned minSampleRate = 8000;
const unsigned maxSampleRate = 192000;

namespace WebCore {

PassRefPtr<MediaElementAudioSourceNode> MediaElementAudioSourceNode::create(AudioContext* context, HTMLMediaElement* mediaElement)
{
    return adoptRef(new MediaElementAudioSourceNode(context, mediaElement));
}

MediaElementAudioSourceNode::MediaElementAudioSourceNode(AudioContext* context, HTMLMediaElement* mediaElement)
    : AudioSourceNode(context, context->sampleRate())
    , m_mediaElement(mediaElement)
    , m_sourceNumberOfChannels(0)
    , m_sourceSampleRate(0)
{
    ScriptWrappable::init(this);
    // Default to stereo. This could change depending on what the media element .src is set to.
    addOutput(adoptPtr(new AudioNodeOutput(this, 2)));

    setNodeType(NodeTypeMediaElementAudioSource);

    initialize();
}

MediaElementAudioSourceNode::~MediaElementAudioSourceNode()
{
    m_mediaElement->setAudioSourceNode(0);
    uninitialize();
}

void MediaElementAudioSourceNode::setFormat(size_t numberOfChannels, float sourceSampleRate)
{
    if (numberOfChannels != m_sourceNumberOfChannels || sourceSampleRate != m_sourceSampleRate) {
        if (!numberOfChannels || numberOfChannels > AudioContext::maxNumberOfChannels() || sourceSampleRate < minSampleRate || sourceSampleRate > maxSampleRate) {
            // process() will generate silence for these uninitialized values.
            WTF_LOG(Media, "MediaElementAudioSourceNode::setFormat(%u, %f) - unhandled format change", static_cast<unsigned>(numberOfChannels), sourceSampleRate);
            m_sourceNumberOfChannels = 0;
            m_sourceSampleRate = 0;
            return;
        }

        m_sourceNumberOfChannels = numberOfChannels;
        m_sourceSampleRate = sourceSampleRate;

        // Synchronize with process().
        Locker<MediaElementAudioSourceNode> locker(*this);

        if (sourceSampleRate != sampleRate()) {
            double scaleFactor = sourceSampleRate / sampleRate();
            m_multiChannelResampler = adoptPtr(new MultiChannelResampler(scaleFactor, numberOfChannels));
        } else {
            // Bypass resampling.
            m_multiChannelResampler.clear();
        }

        {
            // The context must be locked when changing the number of output channels.
            AudioContext::AutoLocker contextLocker(context());

            // Do any necesssary re-configuration to the output's number of channels.
            output(0)->setNumberOfChannels(numberOfChannels);
        }
    }
}

void MediaElementAudioSourceNode::process(size_t numberOfFrames)
{
    AudioBus* outputBus = output(0)->bus();

    if (!mediaElement() || !m_sourceNumberOfChannels || !m_sourceSampleRate) {
        outputBus->zero();
        return;
    }

    // Use a tryLock() to avoid contention in the real-time audio thread.
    // If we fail to acquire the lock then the HTMLMediaElement must be in the middle of
    // reconfiguring its playback engine, so we output silence in this case.
    MutexTryLocker tryLocker(m_processLock);
    if (tryLocker.locked()) {
        if (AudioSourceProvider* provider = mediaElement()->audioSourceProvider()) {
            if (m_multiChannelResampler.get()) {
                ASSERT(m_sourceSampleRate != sampleRate());
                m_multiChannelResampler->process(provider, outputBus, numberOfFrames);
            } else {
                // Bypass the resampler completely if the source is at the context's sample-rate.
                ASSERT(m_sourceSampleRate == sampleRate());
                provider->provideInput(outputBus, numberOfFrames);
            }
        } else {
            // Either this port doesn't yet support HTMLMediaElement audio stream access,
            // or the stream is not yet available.
            outputBus->zero();
        }
    } else {
        // We failed to acquire the lock.
        outputBus->zero();
    }
}

void MediaElementAudioSourceNode::lock()
{
    ref();
    m_processLock.lock();
}

void MediaElementAudioSourceNode::unlock()
{
    m_processLock.unlock();
    deref();
}

} // namespace WebCore

#endif // ENABLE(WEB_AUDIO)