demuxing

Demuxing, short for demultiplexing, is the process of separating multiple synchronized data streams that were combined into a single multiplexed stream into their individual constituent streams. It is the inverse operation of multiplexing. Demuxing is used in digital broadcasting, file containers, and streaming to enable independent processing of each stream, such as video, audio, and subtitles, by respective decoders.

In practice, a demultiplexer reads a multiplexed source, identifies the stream types and boundaries using container metadata or transport headers, and outputs the elementary streams. It may preserve timing information (timestamps) to keep streams synchronized during playback. Demuxing can occur at different layers: hardware demultiplexers in set-top boxes or tuners, and software demuxers in media players and video editors. There is a distinction between demuxing container formats (parsing MP4, MKV, AVI, MPEG-TS) and demuxing raw multiplexed streams (for example MPEG-TS packets containing video and audio PES packets).

Common formats used in demuxing include MPEG-TS (transport stream) used in broadcasting, MP4 and MKV containers used for file storage, and WAV or AIFF for audio-only data. After demuxing, the separated streams are typically passed to dedicated decoders (video decoder, audio decoder) for reconstruction of the original media. Demuxing is a prerequisite step for playback, editing, and transcoding, and is designed to be lossless with respect to stream separation, though subsequent encoding/decoding may introduce quality changes.