transcoding

Transcoding is the process of converting digital media from one encoding to another. It can involve changing the video or audio codecs, the container format, the resolution, frame rate, or bitrate of a file or stream. Transcoding typically entails decoding the source media to an intermediate representation and then re-encoding it into the target format. The operation is common in media workflows that require compatibility or adaptation across devices and networks.

Transcoding is often contrasted with transmuxing, where the encoding is not changed but the container is reformatted, and with transrating, where the bitrate is adjusted without altering the codec or resolution. In practice, the term transcoding is sometimes used broadly to describe any conversion that involves re-encoding.

Applications include streaming services that deliver multiple renditions to accommodate varying bandwidth and device capabilities, on-the-fly transcoding in content delivery networks, archival workflows that standardize files for delivery, and publishing pipelines that prepare content for different platforms. Transcoding may be performed on premises with CPUs or GPUs or in cloud services that offer scalable media processing.

Quality considerations are important: re-encoding can introduce compression artifacts and quality loss, especially when reducing bitrate or changing codec settings. Computational costs, latency, and energy use depend on resolution, codec, and hardware acceleration. Metadata, timecodes, and subtitles must be preserved or remapped during the process.

Common codecs include H.264/AVC, H.265/HEVC, VP9, and AV1 for video, and AAC, MP3, and Opus for audio. Container formats such as MP4, MKV, and WebM can carry transcoded streams, while streaming protocols like HLS and MPEG-DASH describe delivery of multiple transcoded renditions.