Rolling back to video conversion, back to alpha

An untested bug in the audio-only conversion process removes video data
from video files. Audio-only conversion will be removed for now.
Since the program is now video-only, the phase is back to alpha.
Removed beta in credits to alpha.
Rollback to alpha-goodbye audio only

Audio-only conversion renders video conversion useless. While a fix is
being carried out, restoring to alpha. Current version: (0.2 Alpha-Video
only)