MediaTrackSettings: latency property
  The MediaTrackSettings dictionary's
  latency property is a double-precision floating-point
  number indicating the estimated latency (specified in seconds) of the
  MediaStreamTrack as currently configured. This lets you determine what
  value was selected to comply with your specified constraints for this property's value
  as described in the MediaTrackConstraints.latency property you provided
  when calling either getUserMedia() or
  MediaStreamTrack.applyConstraints().
This is, of course, an approximation, since latency can vary for many reasons including CPU, transmission, and storage overhead.
  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.
Value
A double-precision floating-point number indicating the estimated latency, in seconds, of the audio track as currently configured.
Examples
See the Constraint exerciser example.
Specifications
| Specification | 
|---|
| Media Capture and Streams # dom-mediatrackconstraintset-latency | 
Browser compatibility
BCD tables only load in the browser