ffmpeg filter syntax

The general syntax of a filter is:-

"[incoming-feed] filtername=paramater1=value:param2=value [result-name]"

Filters may be chained together so the output of one feeds the input to the next, in this case the "[incoming-feed]" and "[result-name]" parts are removed as they are assumed, and the filters separated by a comma ","
Chains may be put together to form a "filtergraph". The chains are separated from each other by a semicolon ";". Because of the possibility for branching and merging (c.f the overlay filter) and to allow for complex filtering it is necessary to use the "[incoming-feed]" and "[result-name]" parts to join the relevant inputs and outputs. For example:-

-vf "movie=logo-rgb.png [logo] ; [logo] scale=100:100 [resized]; [in][resized] overlay [out]"


Since a graph may contain a single chain which contains a single filter the following are equivalent:-

-vf "[in] scale 720:576 [out]"

-vf "scale 720:576"

as are the slightly more complex, but trivial

-vf "[in] scale 720:576 [scaled] ; [scaled] null [out]"

-vf "scale 720:576 , null"