I'm just struggling with a similar problem. The QT API parts which are necessary to extract the audio data are simply not available to 64-bit applications. All relevant posts to get any audio data refer to MovieAudioExtractionFillBuffer and the like.
My solution will be an application and project split, thus I will have a 32-bit audio extractor process and a 64-bit main application process using some IPC memory transfer to get the audio data around.