Updated the modifications made in Sickbeard mp4 automator to the latest
version of python-video-converter in such a way that they are backwards
compatible with prior version unlike my last pull attempt.

Changes made here add the ability to output files with multiple audio
and subtitle tracks taking advantage of FFMPEGs -map function. Can pull
from multiple or single sources. to create complex files with different
tracks.

Options are presented as nested dictionaries now but previously used
style dictionaries are still compatible.

Tests will need to be updated

makes it more compliant with how the script functioned previously
(allows it to pass some of the tests)

reorganizes commands

for python 3 compatibility

-option to pass ffmpeg options before the inputfile and before the
output file when needed. Being used for things like `-fix_sub_duration`
and `-threads auto`. Defaults to none.
-unicodedecodeerror exception catching which can occur with certain
characters in file names breaking the script

-support for passing audio filters using the `filter` option
-bitrates violating the min or max are approximated to their closest
min/max value to avoid ffmpeg crashing due to absence of any bitrate
setting
-do not allow ac3 channels > 6. AC3 does not support any channel
settings greater than 5.1 and will cause ffmpeg to abort

includes the minimum bitrate

ffprobe read video level