The MediaTrackConstraints dictionary is used to describe a set of capabilities and the value or values each can take on. A constraints dictionary is passed into applyConstraints() to allow a script to establish a set of exact (required) values or ranges and/or preferred values or ranges of values for the track, and the most recently-requested set of custom constraints can be retrieved by calling getConstraints().
For each constraint, you can typically specify an exact value you need, an ideal value you want, a range of acceptable values, and/or a value which you'd like to be as close to as possible. The specifics vary somewhat depending on the type of the constrainable property.
To learn more about how constraints work, see Capabilities, constraints, and settings.
Properties
Some combination—but not necessarily all—of the following properties will exist on the object.
Properties of all media tracks
deviceId- A
ConstrainDOMStringobject specifying a device ID or an array of device IDs which are acceptable and/or required. groupId- A
ConstrainDOMStringobject specifying a group ID or an array of group IDs which are acceptable and/or required.
Properties of audio tracks
channelCount- A
ConstrainLongspecifying the channel count or range of channel counts which are acceptable and/or required. echoCancellation- A
ConstrainBooleanobject specifying whether or not echo cancellation is required or preferred and/or required. latency- A
ConstrainDoublespecifying the latency or range of latencies which are acceptable and/or required. sampleRate- A
ConstrainLongspecifying the sample rate or range of sample rates which are acceptable and/or required. sampleSize- A
ConstrainLongspecifying the sample size or range of sample sizes which are acceptable and/or required. volume- A
ConstrainDoublespecifying the volume or range of volumes which are acceptable and/or required.
Properties of video tracks
aspectRatio- A
ConstrainDoublespecifying the video aspect ratio or range of aspect ratios which are acceptable and/or required. facingMode- A
ConstrainDOMStringobject specifying a facing or an array of facings which are acceptable and/or required. frameRate- A
ConstrainDoublespecifying the frame rate or range of frame rates which are acceptable and/or required. height- A
ConstrainLongspecifying the video height or range of heights which are acceptable and/or required. width- A
ConstrainLongspecifying the video width or range of widths which are acceptable and/or required.