Yeah, but the article is already quite long so I omit the "details" on that... Basically, it's just to specify a complex filtergraph: in the case of -vf you're

Yeah, but the article is already quite long so I omit the "details" on that... Basically, it's just to specify a complex filtergraph: in the case of -vf you're just passing one video stream which gets filtered by successive filters. In the case of -lavfi (or -filter_complex if you prefer) you can feed multiple inputs (and get multiple outputs). In this case, the second input is the palette image. You can find more information on http://ffmpeg.org/ffmpeg-filters.html#Filtering-Introduction http://ffmpeg.org/ffmpeg-filters.html#Filtering-Introduction