vtl: update ffmpeg option sameq/qscale
vtl: use avi/mjpeg (insted of mpeg4) for video proxy

 * average picture quality is worse
 * ..but seeking works accurately
   (no more PTS/DTS mess with Quicktime files)
 * ffmpeg transcode to mpeg4 retains PTS, DTS ( to mjpeg does not)
 * eventually harvid&xjadeo need to be
   updated to seek to non-monotonic PTS, DTS timestamps