You haven't posted all your code and it looks, to me, that you are starting the video through your method_play method, which is happening on the primary thread.

It looks like you are making you main thread sleep when you pause processing, and you end up hanging your UI. You need to have a separate thread for running your audio to text conversion code so that, you can pause that thread as an when required. (Hint: see System.ComponentModel.BackgroundWorker documentation) Please explain how your code works, may be then we will be able to help you better.