* add more supported file types to our media processor that ffmpeg supports, update supported mime type lists
* add code comments to the supported mime types slice
* don't check for zero value string, just parse
* remove some unneeded consts which make the code a bit harder to read
* fix test expected instance media mime types, use compact ffprobe json, simple media processing by type
* final tweaks to media processing code
* don't use safe divide where we don't need to
