ARA Demo Plugin is broken

Audio Plugins
1

The way ARA Audio readers are being used does not align with the requirements.

See ARA docs: ARA::PlugIn::HostAudioAccessController::createAudioReaderForSource

To stop shooting myself into the foot, I added simple stacktrace validation for debug builds:

    void validateStackTrace()
    {
#ifndef JUCE_DEBUG
        return;
#endif

        const auto backtrace = SystemStats::getStackBacktrace();
        StringArray validMethods {
            "doCreateAudioSource",
            "doDestroyAudioSource",
            "willUpdateAudioSourceProperties",
            "didUpdateAudioSourceProperties",
            "doUpdateAudioSourceContent",
            "willEnableAudioSourceSamplesAccess",
            "didEnableAudioSourceSamplesAccess",
            "willDeactivateAudioSourceForUndoHistory",
            "didDeactivateAudioSourceForUndoHistory",
            "didAddAudioModificationToAudioSource",
            "willRemoveAudioModificationFromAudioSource",
            "willDestroyAudioSource",
            "didEndEditing"
        };

        for (const auto& method : validMethods)
        {
            if(backtrace.contains(method))
                return;
        }

        /*
         * The ARA::PlugIn::HostAudioReader (hostReader member) can only be created or destroyed during audio source management hooks in the document controller.
         * It wraps ARAAudioAccessControllerInterface, so see ARAAudioAccessControllerInterface::createAudioReaderForSource and ARAAudioAccessControllerInterface::destroyAudioReader for documentation.
         */
        jassertfalse;
    }

ARAAudioSourceReader::ARAAudioSourceReader (ARAAudioSource* audioSource)
    : AudioFormatReader (nullptr, "ARAAudioSourceReader"),
      audioSourceBeingRead (audioSource)
{
    jassert (audioSourceBeingRead != nullptr);

    bitsPerSample = 32;
    usesFloatingPointData = true;
    sampleRate = audioSourceBeingRead->getSampleRate();
    numChannels = (unsigned int) audioSourceBeingRead->getChannelCount();
    lengthInSamples = audioSourceBeingRead->getSampleCount();
    tmpPtrs.resize (numChannels);

    audioSourceBeingRead->addListener (this);

    validateStackTrace();
    if (audioSourceBeingRead->isSampleAccessEnabled())
        hostReader.reset (new ARA::PlugIn::HostAudioReader (audioSourceBeingRead));
}

In practice this does cause issues in some hosts, from the top of my head I remember Cubase and Nuendo.

2

Just to clarify — are you saying that a plugin shouldn’t request audio source readers from the host on the GUI thread (or at arbitrary times)?

3

The plugin must create readers from the gui thread, only during the audio source management ara hooks, or endEditing.

ARA Docs:

Create audio reader instance to access sample data in an audio source. The format of the data is matching the format of the audio source, with a choice of reading samples as 32 bit or 64 bit (hosts must support both formats). Similar to the rules for creating content readers, the plug-in may call these functions only from calls in the “Audio Source Management” section of ARADocumentControllerInterface for the particular audio source the call is referring to, or from ARADocumentControllerInterface::endEditing() for any audio source. Contrary to content readers, audio readers are long-living objects that are not bound to a certain stack frame.

1 Like