Does not properly support -ss, -to or -t ffmpeg options

[Alexey-Akishin]

Progress bar does not work as expected if only portion of input file is used because of -ss and -to or -t options.

[solonovamax]

To add on (not different enough to warrant its own issue): It will break when using a filter like: ffmpeg -i input.mkv -c:v libx264 -crf 0 -filter_complex "[0:v]setpts=4.0*PTS[v];[0:a]atempo=0.5,atempo=0.5[a]".

When the bar goes past the number of estimated frames, it will just disappear. (Eg. if ffpb guesses the output will have 600 frames and it goes to 660, then the output will look like this: input.mkv: 780 frames [05:48, 2.17 frames/s]