[Feature] Advanced support for filter chaining (filtergraph)

[belgattitude]

FFMpeg support filtergraph notation:

Do we support it ?

Supporting it will make the API more verbose... and we can always create an 'handmade' filter:

<?php
$myComplexFilter = new class interface FFMpegVideoFilterInterface {
   public function getFFmpegCLIValue(): string
    {
        return '[in]yadif=0:0:0[middle];[middle]scale=iw/2:-1[out]';
    }
}

I think we should not and document instead.

Any thoughts ?

See : https://trac.ffmpeg.org/wiki/FilteringGuide and http://ffmpeg.org/ffmpeg-filters.html#Filtergraph-description

[belgattitude]

Linked to #9