Allow mp4 processor - allow external mp4 files.

[ferzu13]

not all mp4 files are encoded similarly, allow for mp4 not made from our recorder

- we can only process .mp4 and only 1 type of encoding H264
- can not pass fractional fps less than 1 #5 
- this is related to web capture and upload, standalone processor CLI accepting files not created with it.

currently we are using mini-mp4 > solution get rid of that and use ffmpeg directly