[SUGGESTION] FFMPEG color space "legalization"

This feature will help all videomakers to "legalize" color space produced by their cameras for broadcast standard.

All started from [this discussion](https://video.stackexchange.com/questions/29699/canon-rgb-color-space-shift-to-broadcast-range-with-ffmpeg) started by me for solving the problem with "Canon HF100 colorspace".

After evaluating a clip, [Gyan](https://video.stackexchange.com/users/1871/gyan) (an FFMPEG maintainer) suggested me:

> You can use the geq filter to remap the pixel value ranges.
>
> `ffmpeg`
> `-i input`
> `-vf "geq=lum='(p(X,Y)-16)/(255-16)*(235-16)+16':cb='(p(X,Y)-16)/(255-16)*(240-16)+16'"`
> `-c:v libx264 -c:a copy out.mp4`
>
>The geq filter rescales the input luma from 16-255 to 16-235, and both the input chroma from 16-255 to 16-240, which is the legal range for broadcast 8-bit signals.

Hope that inspires !