Improved H.264 support and exit status

- H264 support is improved by adding video output quality options and
output video size adjustment.
- Updates ffmpeg call with [Create a video slideshow from
images](https://trac.ffmpeg.org/wiki/Create%20a%20video%20slideshow%20fr
om%20images)
- Exit status is captured enabling errors to be caught and potentially
executing cleanMP4 script.
Demo updated with H.264 MP4 support

- Updates demo with libx264 codec for MP4 output.
- Video output resolution is defined and set.