Transmuxing, short for transport stream multiplexing, is a process that changes the container format of a video without altering its underlying audio or video data. It is commonly used in video streaming to make content compatible with different devices and platforms, ensuring seamless playback.

Videos are made up of two main parts: the actual audio and video data (encoded using codecs like H.264 or AAC) and the container format (such as MP4, MKV, or MPEG-TS). The container acts like a wrapper, organizing the audio, video, and metadata into a single file.

Transmuxing involves taking the encoded audio and video data and placing it into a new container format. For example, an MP4 video can be transmuxed into an HLS (HTTP Live Streaming) or DASH (Dynamic Adaptive Streaming over HTTP) format. This process is fast because it doesn't require re-encoding the video, only repackaging it.