MediaTrackConstraints

TheMediaTrackConstraints dictionary is used to describe a set of media capabilities and the value or values each can take on.

A constraints dictionary is passed into theapplyConstraints() method of theMediaStreamTrack interface 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.

The most recently-requested set of custom constraints can be retrieved by callinggetConstraints().

Objects of this type may also be passed to:

TheMediaDevices.getUserMedia() method, to specify constraints on a media stream requested from hardware such as a camera or microphone.
TheMediaDevices.getDisplayMedia() method, to specify constraints on a media stream requested from a screen or window capture.

Constraints

The following types are used to specify a constraint for a property.They allow you to specify one or moreexact values from which one must be the parameter's value, or a set ofideal values which should be used if possible.You can also specify a single value (or an array of values) which the user agent will do its best to match once all more stringent constraints have been applied.

To learn more about how constraints work, seeCapabilities, constraints, and settings.

Note:min andexact values are not permitted in constraints used inMediaDevices.getDisplayMedia() calls — they produce aTypeError — but they are allowed in constraints used inMediaStreamTrack.applyConstraints() calls.

ConstrainBoolean

TheConstrainBoolean constraint type is used to specify a constraint for a property whose value is a Boolean value.Its value may either be set to a Boolean (true orfalse) or an object containing the following properties:

exact: A Boolean which must be the value of the property.If the property can't be set to this value, matching will fail.
ideal: A Boolean specifying an ideal value for the property.If possible, this value will be used, but if it's not possible, the user agent will use the closest possible match.

ConstrainBooleanOrDOMString

TheConstrainBooleanOrDOMString constraint type is used to specify a constraint for a property whose value is a Boolean or string value. It can take values as specified in theConstrainBoolean andConstrainDOMString sections.

ConstrainDouble

TheConstrainDouble constraint type is used to specify a constraint for a property whose value is a double-precision floating-point number.Its value may either be set to a number or an object containing the following properties:

max: A decimal number specifying the largest permissible value of the property it describes.If the value cannot remain equal to or less than this value, matching will fail.
min: A decimal number specifying the smallest permissible value of the property it describes.If the value cannot remain equal to or greater than this value, matching will fail.
exact: A decimal number specifying a specific, required, value the property must have to be considered acceptable.
ideal: A decimal number specifying an ideal value for the property.If possible, this value will be used, but if it's not possible, the user agent will use the closest possible match.

ConstrainDOMString

TheConstrainDOMString constraint type is used to specify a constraint for a property whose value is a string.Its value may either be set to a string, an array of strings, or an object containing the following properties:

exact: A string or an array of strings, one of which must be the value of the property.If the property can't be set to one of the listed values, matching will fail.
ideal: A string or an array of strings, specifying ideal values for the property.If possible, one of the listed values will be used, but if it's not possible, the user agent will use the closest possible match.

ConstrainULong

TheConstrainULong constraint type is used to specify a constraint for a property whose value is an integer.Its value may either be set to a number or an object containing the following properties:

max: An integer specifying the largest permissible value of the property it describes.If the value cannot remain equal to or less than this value, matching will fail.
min: An integer specifying the smallest permissible value of the property it describes.If the value cannot remain equal to or greater than this value, matching will fail.
exact: An integer specifying a specific, required, value the property must have to be considered acceptable.
ideal: An integer specifying an ideal value for the property.If possible, this value will be used, but if it's not possible, the user agent will use the closest possible match.

Instance properties

Some combination—but not necessarily all—of the following properties will exist on the object.This may be because a given browser doesn't support the property, or because it doesn't applyFor example, becauseRTP doesn't provide some of these values during negotiation of a WebRTC connection, a track associated with aRTCPeerConnection will not include certain values, such asfacingMode orgroupId.

Instance properties of all media tracks

deviceId: AConstrainDOMString object specifying a device ID or an array of device IDs which are acceptable and/or required.
groupId: AConstrainDOMString object specifying a group ID or an array of group IDs which are acceptable and/or required.

Instance properties of audio tracks

autoGainControl: AConstrainBoolean object which specifies whether automatic gain control is preferred and/or required.
channelCount: AConstrainULong specifying the channel count or range of channel counts which are acceptable and/or required.
echoCancellation: AConstrainBooleanOrDOMString object specifying whether or not echo cancellation is preferred and/or required, and if supported, what type.
latency: AConstrainDouble specifying the latency or range of latencies which are acceptable and/or required.
noiseSuppression: AConstrainBoolean which specifies whether noise suppression is preferred and/or required.
sampleRate: AConstrainULong specifying the sample rate or range of sample rates which are acceptable and/or required.
sampleSize: AConstrainULong specifying the sample size or range of sample sizes which are acceptable and/or required.
volumeDeprecated Non-standard: A ConstrainDouble specifying the volume or range of volumes which are acceptable and/or required.

Instance properties of image tracks

whiteBalanceMode: AString specifying one of"none","manual","single-shot", or"continuous".
exposureMode: AString specifying one of"none","manual","single-shot", or"continuous".
focusMode: AString specifying one of"none","manual","single-shot", or"continuous".
pointsOfInterest: The pixel coordinates on the sensor of one or more points of interest.This is either an object in the form { x:value, y:value } or an array of such objects, wherevalue is a double-precision integer.
exposureCompensation: AConstrainDouble (a double-precision integer) specifying f-stop adjustment by up to ±3.
colorTemperature: AConstrainDouble (a double-precision integer) specifying a desired color temperature in degrees kelvin.
iso: AConstrainDouble (a double-precision integer) specifying a desired iso setting.
brightness: AConstrainDouble (a double-precision integer) specifying a desired brightness setting.
contrast: AConstrainDouble (a double-precision integer) specifying the degree of difference between light and dark.
saturation: AConstrainDouble (a double-precision integer) specifying the degree of color intensity.
sharpness: AConstrainDouble (a double-precision integer) specifying the intensity of edges.
focusDistance: AConstrainDouble (a double-precision integer) specifying distance to a focused object.
zoom: AConstrainDouble (a double-precision integer) specifying the desired focal length.
torch: A boolean value defining whether the fill light is continuously connected, meaning it stays on as long as the track is active.

Instance properties of video tracks

aspectRatio

AConstrainDouble specifying the videoaspect ratio or range of aspect ratios which are acceptable and/or required.

facingMode

AConstrainDOMString object specifying a facing or an array of facings which are acceptable and/or required.

frameRate

AConstrainDouble specifying the frame rate or range of frame rates which are acceptable and/or required.

height

AConstrainULong specifying the video height or range of heights which are acceptable and/or required.

width

AConstrainULong specifying the video width or range of widths which are acceptable and/or required.

resizeMode

AConstrainDOMString object specifying a mode or an array of modes the UA can use to derive the resolution and frame rate of a video track.Allowed values are:

crop-and-scale: The user agent can use cropping and downscaling of resolution or frame rate on the raw output from the hardware/OS, in order to satisfy other constraints.This constraint allows developers to get a downscaled video even if the particular format indicated by their constraints is not natively supported by the hardware.
none: The user agent uses the resolution provided by the underlying hardware, such as a camera or its driver, or the OS.

IfresizeMode is unspecified the browser will choose a resolution based on afitness distance that considers the specified constraints andboth of the allowed values.

Instance properties of shared screen tracks

These constraints apply to thevideo property of the object passed intogetDisplayMedia() to obtain a stream for screen sharing.

displaySurface

AConstrainDOMString which specifies the types of display surface that may be selected by the user.This may be a single one of the following strings, or a list of them to allow multiple source surfaces:

browser: The stream contains the contents of a single browser tab selected by the user.
monitor: The stream's video track contains the entire contents of one or more of the user's screens.
window: The stream contains a single window selected by the user for sharing.

logicalSurface

AConstrainBoolean value which may contain a single Boolean value or a set of them, indicating whether or not to allow the user to choose source surfaces which do not directly correspond to display areas.These may include backing buffers for windows to allow capture of window contents that are hidden by other windows in front of them, or buffers containing larger documents that need to be scrolled through to see the entire contents in their windows.

suppressLocalAudioPlaybackExperimental

A ConstrainBoolean value describing the requested or mandatory constraints placed upon the value of thesuppressLocalAudioPlayback constrainable property.This property controls whether the audio playing in a tab will continue to be played out of a user's local speakers when the tab is captured.

restrictOwnAudioExperimental

A ConstrainBoolean value that specifies the requested or mandatory constraints placed on the value of therestrictOwnAudio constrainable property.This property controls whether the system audio originating from the capturing tab is filtered out of the screen capture.

Specifications

Specification
Media Capture and Streams # dom-mediatrackconstraints
Screen Capture # extensions-to-mediatrackconstraintset

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