diff --git a/doc/filters.texi b/doc/filters.texi index 2803c67fd2..158b74b3ae 100644 --- a/doc/filters.texi +++ b/doc/filters.texi @@ -3,10 +3,10 @@ Filtering in FFmpeg is enabled through the libavfilter library. -In libavfilter, it is possible for filters to have multiple inputs and -multiple outputs. -To illustrate the sorts of things that are possible, we can -use a complex filtergraph. For example, the following one: +In libavfilter, a filter can have multiple inputs and multiple +outputs. +To illustrate the sorts of things that are possible, we consider the +following filtergraph. @example input --> split ---------------------> overlay --> output @@ -15,25 +15,32 @@ input --> split ---------------------> overlay --> output +-----> crop --> vflip -------+ @end example -splits the stream in two streams, sends one stream through the crop filter -and the vflip filter before merging it back with the other stream by -overlaying it on top. You can use the following command to achieve this: +This filtergraph splits the input stream in two streams, sends one +stream through the crop filter and the vflip filter before merging it +back with the other stream by overlaying it on top. You can use the +following command to achieve this: @example -ffmpeg -i input -vf "[in] split [T1], [T2] overlay=0:H/2 [out]; [T1] crop=iw:ih/2:0:ih/2, vflip [T2]" output +ffmpeg -i INPUT -vf "split [main][tmp]; [tmp] crop=iw:ih/2:0:0, vflip [flip]; [main][flip] overlay=0:H/2" OUTPUT @end example The result will be that in output the top half of the video is mirrored onto the bottom half. -Filters are loaded using the @var{-vf} or @var{-af} option passed to -@command{ffmpeg} or to @command{ffplay}. Filters in the same linear -chain are separated by commas. In our example, @var{split, -overlay} are in one linear chain, and @var{crop, vflip} are in -another. The points where the linear chains join are labeled by names -enclosed in square brackets. In our example, that is @var{[T1]} and -@var{[T2]}. The special labels @var{[in]} and @var{[out]} are the points -where video is input and output. +Filters in the same linear chain are separated by commas, and distinct +linear chains of filters are separated by semicolons. In our example, +@var{crop,vflip} are in one linear chain, @var{split} and +@var{overlay} are separately in another. The points where the linear +chains join are labelled by names enclosed in square brackets. In the +example, the split filter generates two outputs that are associated to +the labels @var{[main]} and @var{[tmp]}. + +The stream sent to the second output of @var{split}, labelled as +@var{[tmp]}, is processed through the @var{crop} filter, which crops +away the lower half part of the video, and then vertically flipped. The +@var{overlay} filter takes in input the first unchanged output of the +split filter (which was labelled as @var{[main]}), and overlay on its +lower half the output generated by the @var{crop,vflip} filterchain. Some filters take in input a list of parameters: they are specified after the filter name and an equal sign, and are separated from each other