libavfilter

libavfilter is the filtering library component of FFmpeg, providing a generic framework for applying visual and audio filters to multimedia streams. It implements a graph-based model in which filters are nodes connected by input and output pads, enabling flexible chaining, mixing, and routing of data from sources to sinks.

The core concepts include AVFilter, which defines a filter’s behavior; AVFilterContext, which represents an instantiated filter; and AVFilterGraph, which describes a network of filters. Special filters such as buffersrc (a source that feeds frames into a graph) and buffersink (a sink that retrieves filtered frames) are used to connect a program’s data stream into and out of the graph. Filter graphs can be built programmatically or described as textual graphs used with the -filter_complex or -filter options in FFmpeg tooling.

libavfilter supports a wide range of built-in filters for both video and audio processing. Video filters cover scaling, cropping, colorspace conversion, rotation, overlays, drawing text, deinterlacing, and more. Audio filters include volume control, tempo and pitch adjustments, equalization, delays, and various effects. Complex pipelines can combine multiple filters, branch data through fan-out paths, and mix inputs.

In typical usage, an application creates and configures a filter graph, feeds frames into buffersrc, advances the graph, and retrieves results from buffersink. It integrates with other FFmpeg libraries (libavutil, libavcodec) to handle decoding, encoding, and buffer management, and is accessible from both command-line tools and custom software.