There are so-called source filters that do not take video input, and we expect that some sink filters will not have video output, at some point in the future. Some filters take a list of parameters: they are specified after the filter name and an equal sign, and are separated by a semicolon. The magic labels and are the points where video is input and output. The points where the linear chains join are labeled by names enclosed in square brackets. In our example, split, fifo, and overlay are in one linear chain, and fifo, crop, and vflip are in another. Filters in the same linear chain are separated by commas. Video filters are loaded using the -vf option passed to avconv or to avplay. The result will be that the top half of the video is mirrored onto the bottom half of the output video. avconv -i input -vf " split, fifo, overlay=0:H/2 fifo, crop=iw:ih/2:0:ih/2, vflip " output You can use the following command to achieve this: Splits the stream in two streams, then sends one stream through the crop filter and the vflip filter, before merging it back with the other stream by overlaying it on top.
Input -> split -> fifo -> overlay -> output To illustrate the sorts of things that are possible, we can use a complex filter graph. In libavfilter, it is possible for filters to have multiple inputs and multiple outputs.
Note that there may still be serious bugs in the code and its API and ABI should not be considered stable yet! It replaces ’vhooks’, and started as a Google Summer of Code project.
Libavfilter is the filtering API of Libav.
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