The RTCRtpSynchronizationSource dictionary of the the WebRTC API is used by getSynchronizationSources() to describe a particular synchronization source (SSRC). A synchronization source is a single source that shares timing and sequence number space. Since RTCRtpSynchronizationSource implements RTCRtpContributingSource, its properties are also available.

The information provided is based on the last ten seconds of media received.

While the published specification describes this as an interface, it has since been changed to a dictionary in follow-up drafts.


Also implements the properties of RTCRtpContributingSource.

voiceActivityFlag Optional
A Boolean value indicating whether or not voice activity is included in the last RTP packet played from the source. If the peer has indicated that it's not supporting voice activity detection, this field is not provided.


Specification Status Comment
WebRTC 1.0: Real-time Communication Between Browsers
The definition of 'RTCRtpSynchronizationSource' in that specification.
Candidate Recommendation Initial definition.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support No ?591 No No ?
voiceActivityFlag No ?591 No No ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support No No ?591 No ? No
voiceActivityFlag No No ?591 No ? No

1. From version 59: this feature is behind the media.peerconnection.rtpsourcesapi.enable preference (needs to be set to true). To change preferences in Firefox, visit about:config.

Document Tags and Contributors

Contributors to this page: fscholz, Sheppy
Last updated by: fscholz,