A media framework is a library, or a family of libraries, that handles the reading, decoding, processing, and output of audio and video. Instead of implementing dozens of codecs and container formats by hand, a developer builds on a framework and concentrates on what their own application does with the media.
Pipeline graphs: filters and sinks
Most media frameworks organize work as a pipeline: a chain of processing steps that media data flows through, like an assembly line. Each step is a filter that does one job, such as decoding a video stream, converting audio between formats, resizing frames, or mixing tracks. At the end of the chain is a sink, the destination for the finished media, such as a display, an audio device, or a file on disk.
Thinking in pipelines pays off. A pipeline can be inspected step by step, reordered, or rerouted to a different sink, and individual filters can be swapped without touching the rest of the chain.
Why frameworks matter
Codecs are complex. A single video codec involves years of specification work and careful optimization, and applications routinely need to support many of them across many platforms. A media framework absorbs that complexity and offers one interface, which makes programs smaller, more portable, and much easier to maintain.
Established open-source examples
Several open-source frameworks have been part of the field for many years. FFmpeg is a widely used set of libraries and command-line tools for reading, writing, and converting audio and video; its libraries are embedded in many other applications. GStreamer takes a plug-in approach, letting developers assemble custom pipelines from many small elements, and is common in desktop environments and embedded devices. MLT focuses on non-linear media editing and powers several video editors, giving scripts fine control over clips, transitions, and timelines.
These are described here as established projects, not as recommendations; the right tool depends on your project and learning goals.
Choosing a framework by learning goals
The best way to choose is to ask what you want to learn. If you want to understand formats and conversions directly, working with FFmpeg from the command line teaches quickly. If you want to learn pipeline thinking, GStreamer's graph of elements makes the concept visible. If your goal is programmatic video editing, MLT's timeline model fits. Start with the framework that matches the concept you are studying, and the others will be easier to pick up later.