The Invalid Selector Message

The auval test itself is predicated on two things:

• An Audio Unit of type kAudioUnitType_Effect ('aufx') does NOT support the MIDI selectors.

• If an Audio Unit of type kAudioUnitType_Effect ('aufx') does support MIDI selectors (which is incorrect according to the Audio Unit Specification), there is no way to determine if the Audio Unit actually implements the selectors or not.

Therefore, to clarify this ambiguity from the Audio Unit host's perspective, auval will now perform this test and fail an Audio Unit it is propagating this ambiguity.

The noErr Message

When auval gets back a noErr from an Audio Unit in this case, the unit must be supporting the kMusicDeviceMIDIEventSelect selector somewhere in the Component Dispatch function.

If the Audio Unit is a subclass of AUBase or AUEffectBase then by default it would not have support for the MIDI selectors. If it is a subclass of AUMIDIBase however, then the entry point is overridden and can be found in AUMIDIBase.cpp:

Listing 1  

ComponentResult AUMIDIBase::ComponentEntryDispatch(ComponentParameters *params, AUMIDIBase *This)
{
    if (This == NULL) return paramErr;

    ComponentResult result;

    switch (params->what) {
    case kMusicDeviceMIDIEventSelect:
        {
            PARAM(UInt32, pbinStatus, 0, 4);
            PARAM(UInt32, pbinData1, 1, 4);
            PARAM(UInt32, pbinData2, 2, 4);
            PARAM(UInt32, pbinOffsetSampleFrame, 3, 4);
            result = This->MIDIEvent(pbinStatus, pbinData1, pbinData2, pbinOffsetSampleFrame);
        }
        break;
    case kMusicDeviceSysExSelect:
        {
            PARAM(const UInt8 *, pbinData, 0, 2);
            PARAM(UInt32, pbinLength, 1, 2);
            result = This->SysEx(pbinData, pbinLength);
        }
        break;

    default:
        result = badComponentSelector;
        break;
    }

    return result;
}

Search for kMusicDeviceMIDIEventSelect and kMusicDeviceSysExSelect as the dispatch code must be accepting these as valid selectors.