Extends the Media Source Extensions API (MSE) to enable buffering containerless WebCodecs encoded media chunks with MSE for low-latency buffering and seekable playback.


MSE requires applications to provide fragments of containerized media (such as fragmented MP4, WebM, or MP3) to be able to buffer and play that media. If the application already has the media in a parsed and structured form, it can cost extra latency and code complexity to package that media into a container and feed it to MSE. As the web platform is evolving to give applications lower-level abstractions for efficiently encoding and decoding media via the WebCodecs API, MSE can use WebCodecs media structures to let applications more efficiently feed their media to MSE. Use cases include simplifying and improving performance of transmuxing HLS-TS into fMP4 for buffering with MSE, and low-latency streaming with a seekable buffer.




Specification link

Specification currently under development in a Working Group

Status in Chromium


Origin trial (tracking bug)

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.


Intent to Prototype url

Intent to Prototype thread

Search tags

MSE, MediaSource, MediaSourceExtensions, WebCodecs, MSE4WC,

Last updated on 2022-02-27