SourceBuffer

Available in workers

The SourceBuffer interface represents a chunk of media to be passed into an HTMLMediaElement and played, via a MediaSource object. This can be made up of one or several media segments.

Instance properties

• appendWindowEnd
  • : Controls the timestamp for the end of the append window.
• appendWindowStart
  • : Controls the timestamp for the start of the append window. This is a timestamp range that can be used to filter what media data is appended to the SourceBuffer. Coded media frames with timestamps within this range will be appended, whereas those outside the range will be filtered out.
• audioTracks Read only
  • : A list of the audio tracks currently contained inside the SourceBuffer.
• buffered Read only
  • : Returns the time ranges that are currently buffered in the SourceBuffer.
• mode
  • : Controls how the order of media segments in the SourceBuffer is handled, in terms of whether they can be appended in any order, or they have to be kept in a strict sequence.
• textTracks Read only Experimental
  • : A list of the text tracks currently contained inside the SourceBuffer.
• timestampOffset
  • : Controls the offset applied to timestamps inside media segments that are subsequently appended to the SourceBuffer.
• updating Read only
  • : A boolean indicating whether the SourceBuffer is currently being updated — i.e., whether an appendBuffer() or remove() operation is currently in progress.
• videoTracks Read only
  • : A list of the video tracks currently contained inside the SourceBuffer.

Instance methods

Inherits methods from its parent interface, EventTarget.

• abort()
  • : Aborts the current segment and resets the segment parser.
• appendBuffer()
  • : Appends media segment data from an ArrayBuffer, a TypedArray or a DataView object to the SourceBuffer.
• appendBufferAsync() Experimental
  • : Starts the process of asynchronously appending the specified buffer to the SourceBuffer. Returns a Promise which is fulfilled once the buffer has been appended.
• changeType()
  • : Changes the MIME type that future calls to appendBuffer() will expect the new data to conform to.
• remove()
  • : Removes media segments within a specific time range from the SourceBuffer.
• removeAsync() Experimental
  • : Starts the process of asynchronously removing media segments in the specified range from the SourceBuffer. Returns a Promise which is fulfilled once all matching segments have been removed.

Events

• abort
  • : Fired when the buffer appending is aborted, because the abort() or removeSourceBuffer() method is called while the appendBuffer() algorithm is still running. updating changes from true to false.
• error
  • : Fired when an error occurs during the processing of an appendBuffer() operation. updating changes from true to false.
• update
  • : Fired whenever appendBuffer() or remove() completes. updating changes from true to false.
• updateend
  • : Fired after the (not necessarily successful) completion of an appendBuffer() or remove() operation. This event is fired after the update, error, or abort events.
• updatestart
  • : Fired when an appendBuffer() or remove() operation begins. updating changes from false to true.

Examples

Loading a video chunk by chunk

The following example loads a video chunk by chunk as fast as possible, playing it as soon as it can.

You can see the complete code at https://github.com/mdn/dom-examples/tree/main/sourcebuffer and try the demo live at https://mdn.github.io/dom-examples/sourcebuffer/.

const video = document.querySelector("video");

const assetURL = "frag_bunny.mp4";
// Need to be specific for Blink regarding codecs
const mimeCodec = 'video/mp4; codecs="avc1.42E01E, mp4a.40.2"';

function loadVideo() {
  if (MediaSource.isTypeSupported(mimeCodec)) {
    const mediaSource = new MediaSource();
    console.log(mediaSource.readyState); // closed
    video.src = URL.createObjectURL(mediaSource);
    mediaSource.addEventListener("sourceopen", sourceOpen);
  } else {
    console.error("Unsupported MIME type or codec: ", mimeCodec);
  }
}

async function sourceOpen() {
  console.log(this.readyState); // open
  const sourceBuffer = this.addSourceBuffer(mimeCodec);
  const response = await fetch(assetURL);
  const buffer = await response.arrayBuffer();
  sourceBuffer.addEventListener("updateend", () => {
    this.endOfStream();
    video.play();
    console.log(this.readyState); // ended
  });
  sourceBuffer.appendBuffer(buffer);
}

const load = document.querySelector("#load");
load.addEventListener("click", loadVideo);

Specifications

Browser compatibility

See also

• MediaSource
• SourceBufferList