MediaTrackConstraints: latency property

The MediaTrackConstraints dictionary's latency property is a ConstrainDouble describing the requested or mandatory constraints placed upon the value of the latency constrainable property.

If needed, you can determine whether or not this constraint is supported by checking the value of MediaTrackSupportedConstraints.latency as returned by a call to MediaDevices.getSupportedConstraints(). However, typically this is unnecessary since browsers will ignore any constraints they're unfamiliar with.

Because RTP doesn't include this information, tracks associated with a WebRTC RTCPeerConnection will never include this property.


A ConstrainDouble describing the acceptable or required value(s) for an audio track's latency, with values specified in seconds. In audio processing, latency is the time between the start of processing (when sound occurs in the real world, or is generated by a hardware device) and the data being made available to the next step in the audio input or output process. In most cases, low latency is desirable for performance and user experience purposes, but when power consumption is a concern, or delays are otherwise acceptable, higher latency might be acceptable.

If this property's value is a number, the user agent will attempt to obtain media whose latency tends to be as close as possible to this number given the capabilities of the hardware and the other constraints specified. Otherwise, the value of this ConstrainDouble will guide the user agent in its efforts to provide an exact match to the required latency (if exact is specified or both min and max are provided and have the same value) or to a best-possible value.

Note: Latency is always prone to some variation due to hardware usage demands, network constraints, and so forth, so even in an "exact" match, some variation should be expected.


See the Constraint exerciser example.


Media Capture and Streams
# dom-mediatrackconstraintset-latency

Browser compatibility

BCD tables only load in the browser

See also