A video filter is a software component that performs some operation on a multimedia stream.^[1] Multiple filters can be used in a chain, known as a filter graph, in which each filter receives input from its upstream filter, processes the input and outputs the processed video to its downstream filter.

With regards to video encoding three categories of filters can be distinguished:

• prefilters: used before encoding
• intrafilters: used while encoding (and are thus an integral part of a video codec)
• postfilters: used after decoding

Common prefilters include:

• denoising
• resizing (upsampling, downsampling)
• contrast enhancement
• deinterlacing (used to convert interlaced video to progressive video)
• deflicking

Common intrafilters include:

• deblocking

Common postfilters include:

• deinterlacing
• deblocking
• deringing

• Filter graph

• Bovik, Al (ed.). Handbook of Image and Video Processing. San Diego: Academic Press, 2000. ISBN 0-12-119790-5.
• Wang, Yao, Jörn Ostermann, and Ya-Qin Zhang. Video Processing and Communications. Signal Processing Series. Upper Saddle River, N.J.: Prentice Hall, 2002. ISBN 0-13-017547-1.