Media Source Extensions

This specification extends HTMLMediaElement [HTML ] to allow JavaScript to generate media streams for playback. Allowing JavaScript to generate streams facilitates a variety of use cases like adaptive streaming and time shifting live streams. This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C standards and drafts index . For a full list of changes made since the previous version, see the commits . The working group maintains a list of all bug reports that the editors have not yet tried to address . Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should track the GitHub repository and take part in the discussions. This document was published by the Media Working Group as a Working Draft using the Recommendation track . Publication as a Working Draft does not imply endorsement by W3C and its Members. This document was produced by a group operating under the W3C Patent Policy . W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent that the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy . This specification allows JavaScript to dynamically construct media streams for and . It defines a MediaSource object that can serve as a source of media data for an HTMLMediaElement. MediaSource objects have one or more SourceBuffer objects. Applications append data segments to the SourceBuffer objects, and can adapt the quality of appended data based on system performance and other factors. Data from the SourceBuffer objects is managed as track buffers for audio, video and text data that is decoded and played. Byte stream specifications used with these extensions are available in the byte stream format registry [MSE-REGISTRY ]. Allow JavaScript to construct media streams independent of how the media is fetched. Define a splicing and buffering model that facilitates use cases like adaptive streaming, ad-insertion, time-shifting, and video editing. Minimize the need for media parsing in JavaScript. Leverage the browser cache as much as possible. Provide requirements for byte stream format specifications. Not require support for any particular media format or codec. Normative behavior for user agents to enable interoperability between user agents and web applications when processing media data. Normative requirements to enable other specifications to define media formats to be used within this specification. The track buffers that provide coded frames for the enabled audioTracks , the selected videoTracks , and the "showing" or "hidden" textTracks . All these tracks are associated with SourceBuffer objects in the activeSourceBuffers list. A presentation timestamp range used to filter out coded frames while appending. The append window represents a single continuous time range with a single start time and end time. Coded frames with presentation timestamp within this range are allowed to be appended to the SourceBuffer while coded frames outside this range are filtered out. The append window start and end times are controlled by the appendWindowStart and appendWindowEnd attributes respectively. The duration of a coded frame . For video and text, the duration indicates how long the video frame or text SHOULD be displayed. For audio, the duration represents the sum of all the samples contained within the coded frame. For example, if an audio frame contained 441 samples @44100