Web/API/MediaTrackConstraints/latency

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 simply 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.

Syntax

var constraintsObject = { latency: constraint };

constraintsObject.latency = constraint;

Value

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.

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.

Example

See Example: Constraint exerciser in Capabilities, constraints, and settings for an example.

Specifications

Specification	Status	Comment
Media Capture and StreamsThe definition of 'latency' in that specification.	Candidate Recommendation	Initial specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`latency`	Chrome Full support 59	Edge Full support ≤79	Firefox Full support 50	IE No support No	Opera Full support Yes	Safari ?	WebView Android Full support 59	Chrome Android Full support 59	Firefox Android Full support 50	Opera Android ?	Safari iOS ?	Samsung Internet Android Full support 7.0

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown