MediaTrackSupportedConstraints - Web APIs 编辑

The MediaTrackSupportedConstraints dictionary establishes the list of constrainable properties recognized by the user agent or browser in its implementation of the MediaStreamTrack object. An object conforming to MediaTrackSupportedConstraints is returned by MediaDevices.getSupportedConstraints().

Because of the way interface definitions in WebIDL work, if a constraint is requested but not supported, no error will occur. Instead, the specified constraints will be applied, with any unrecognized constraints stripped from the request.That can lead to confusing and hard to debug errors, so be sure to use getSupportedConstraints() to retrieve this information before attempting to establish constraints if you need to know the difference between silently ignoring a constraint and a constraint being accepted.

An actual constraint set is described using an object based on the MediaTrackConstraints dictionary.

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.

autoGainControl

A Boolean whose value is true if the autoGainControl constraint is supported in the current environment.

width

A Boolean value whose value is true if the width constraint is supported in the current environment.

height

A Boolean value whose value is true if the height constraint is supported in the current environment.

aspectRatio

A Boolean value whose value is true if the aspectRatio constraint is supported in the current environment.

frameRate

A Boolean value whose value is true if the frameRate constraint is supported in the current environment.

facingMode

A Boolean value whose value is true if the facingMode constraint is supported in the current environment.

resizeMode

A Boolean value whose value is true if the resizeMode constraint is supported in the current environment.

volume

A Boolean value whose value is true if the volume constraint is supported in the current environment.

sampleRate

A Boolean value whose value is true if the sampleRate constraint is supported in the current environment.

sampleSize

A Boolean value whose value is true if the sampleSize constraint is supported in the current environment.

echoCancellation

A Boolean value whose value is true if the echoCancellation constraint is supported in the current environment.

latency

A Boolean value whose value is true if the latency constraint is supported in the current environment.

noiseSuppression

A Boolean whose value is true if the noiseSuppression constraint is supported in the current environment.

channelCount

A Boolean value whose value is true if the channelCount constraint is supported in the current environment.

deviceId

A Boolean value whose value is true if the deviceId constraint is supported in the current environment.

groupId

A Boolean value whose value is true if the groupId constraint is supported in the current environment.

Properties specific to shared screen tracks

For tracks containing video sources from the user's screen contents, the following additional properties are may be included in addition to those available for video tracks.

cursor

A Boolean value which is true if the cursor constraint is supported in the current environment.

displaySurface

A Boolean value which is true if the cursor constraint is supported in the current environment.

logicalSurface

A Boolean value which is true if the logicalSurface constraint is supported in the current environment.

Browser compatibility

BCD tables only load in the browser

See also

• Media Capture and Streams API
• Capabilities, constraints, and settings
• Screen Capture API
• Using the Screen Capture API
• MediaTrackConstraints
• MediaDevices.getUserMedia()
• MediaStreamTrack.getConstraints()
• MediaStreamTrack.applyConstraints()
• MediaStreamTrack.getSettings()