This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

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 error 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.


var myMode = sourceBuffer.mode;

sourceBuffer.mode = 'sequence';


A DOMString.


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

Error 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.
Candidate Recommendation Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 50 25.0 (25.0)[1]
42.0 (42.0)
11[2] 15 8
Feature Android Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 4.4.4

No support

No support 11 30 No support

[1] Available after switching the about:config preference media.mediasource.enabled to true. In addition, support was limited to a whitelist of sites, for example YouTube, Netflix, and other popular streaming sites. The whitelist was removed and Media Source Extensions was enabled by default in 42+ for all sites.

[2] Only works on Windows 8+.

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Audio audio Experimental Media Source Extensions mode MSE Property Reference SourceBuffer video Video