This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The mode property of the SourceBuffer interface controls whether media segments can be appended to the SourceBuffer in any order, or in a strict sequence.

The two available values are:

  • segments: The media segment timestamps determine the order in which the segments are played. The segments can be appended to the SourceBuffer in any order.
  • sequence: The order in which the segments are appended to the SourceBuffer determines the order in which they are played. Segment timestamps are generated automatically for the segments that observe this order.

The mode value is initially set when the SourceBuffer is created using MediaSource.addSourceBuffer(). If timestamps already exist for the media segments, then the value will be set to segments; if they don't, then the value will be set to sequence.

If you try to set the mode property value to segments when the initial value is sequence, an exception will be thrown. The existing segment order must be maintained in sequence mode. You can, however, change the value from segments to sequence. It just means the play order will be fixed, and new timestamps generated to reflect this.

This property cannot be changed during while the SourceBuffer is processing either an appendBuffer() or remove() call.


var myMode = sourceBuffer.mode;

sourceBuffer.mode = 'sequence';


A DOMString.


The following exceptions may be thrown when setting a new value for this property.

Exception Explanation
InvalidAccessError An attempt was made to set the value to segments when the initial value is sequence.
InvalidStateError The SourceBuffer object is being updated (i.e. its SourceBuffer.updating property is currently true), the last media segment appended to this SourceBuffer is incomplete, or this SourceBuffer has been removed from the MediaSource.


This snippet sets the sourceBuffer mode to 'sequence' if it is currently set to 'segments', thus setting the play order to the sequence in which media segments are appended.

var curMode = sourceBuffer.mode;
if (curMode == 'segments') {
  sourceBuffer.mode = 'sequence';


Specification Status Comment
Media Source Extensions
The definition of 'mode' in that specification.
Recommendation Initial definition.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
modeChrome Full support 23Edge Full support 12Firefox Full support 42
Full support 42
No support 25 — 42
Notes Disabled
Notes Limited support to an allowed list of sites, for example YouTube, Netflix, and other popular streaming sites. The limitation was removed when Media Source Extensions was enabled by default in Firefox 42.
Disabled From version 25 until version 42 (exclusive): this feature is behind the media.mediasource.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE Full support 11
Full support 11
Notes Only works on Windows 8+.
Opera Full support 15Safari Full support 8WebView Android Full support 4.4.3Chrome Android Full support 33Firefox Android No support NoOpera Android Full support 14Safari iOS No support NoSamsung Internet Android Full support 3.0


Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also