MediaTrackConstraints

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 .

特性

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 apply. For example, because RTP doesn't provide some of these values during negotiation of a WebRTC connection, a track associated with a RTCPeerConnection will not include certain values, such as facingMode or groupId .

Properties of all media tracks

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

Properties of audio tracks

autoGainControl
A ConstrainBoolean object which specifies whether automatic gain control is preferred and/or required.
channelCount
A ConstrainLong specifying the channel count or range of channel counts which are acceptable and/or required.
echoCancellation
A ConstrainBoolean object specifying whether or not echo cancellation is preferred and/or required.
latency
A ConstrainDouble specifying the latency or range of latencies which are acceptable and/or required.
noiseSuppression
A ConstrainBoolean which specifies whether noise suppression is preferred and/or required.
sampleRate
A ConstrainLong specifying the sample rate or range of sample rates which are acceptable and/or required.
sampleSize
A ConstrainLong specifying the sample size or range of sample sizes which are acceptable and/or required.
volume
A ConstrainDouble specifying the volume or range of volumes which are acceptable and/or required.

Properties of image tracks

whiteBalanceMode
A String specifying one of "none" , "manual" , "single-shot" ,或 "continuous" .
exposureMode
A String specifying one of "none" , "manual" , "single-shot" ,或 "continuous" .
focusMode
A String specifying one of "none" , "manual" , "single-shot" ,或 "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, where value is a double-precision integer.
exposureCompensation
A ConstrainDouble (a double-precision integer) specifying f-stop adjustment by up to ±3.
colorTemperature
A ConstrainDouble (a double-precision integer) specifying a desired color temperature in degrees kelvin.
iso
A ConstrainDouble (a double-precision integer) specifying a desired iso setting.
brightness
A ConstrainDouble (a double-precision integer) specifying a desired brightness setting.
contrast
A ConstrainDouble (a double-precision integer) specifying the degree of difference between light and dark.
saturation
A ConstrainDouble (a double-precision integer) specifying the degree of color intensity.
sharpness
A ConstrainDouble (a double-precision integer) specifying the intensity of edges.
focusDistance
A ConstrainDouble (a double-precision integer) specifying distance to a focused object.
zoom
A ConstrainDouble (a double-precision integer) specifying the desired focal length.
torch
A Boolean defining whether the fill light is continuously connected, meaning it stays on as long as the track is active.

Properties of video tracks

aspectRatio
A ConstrainDouble specifying the video aspect ratio or range of aspect ratios which are acceptable and/or required.
facingMode
A ConstrainDOMString object specifying a facing or an array of facings which are acceptable and/or required.
frameRate
A ConstrainDouble specifying the frame rate or range of frame rates which are acceptable and/or required.
height
A ConstrainLong specifying the video height or range of heights which are acceptable and/or required.
width
A ConstrainLong specifying the video width or range of widths which are acceptable and/or required.
resizeMode
A ConstrainDOMString object specifying a mode or an array of modes the UA can use to derive the resolution of a video track. Allowed values are none and crop-and-scale . none means that the user agent uses the resolution provided by the camera, its driver or the OS. crop-and-scale means that the user agent can use cropping and downscaling on the camera output  in order to satisfy other constraints that affect the resolution.

Properties of shared screen tracks

These constraints apply to MediaTrackConstraints objects specified as part of the DisplayMediaStreamConstraints object's video property when using getDisplayMedia() to obtain a stream for screen sharing.

cursor

A ConstrainDOMString which specifies whether or not to include the mouse cursor in the generated track, and if so, whether or not to hide it while not moving. The value may be a single one of the following strings, or an array of them to allow the browser flexibility in deciding what to do about the cursor.

always
The mouse is always visible in the video content of the {domxref("MediaStream"), unless the mouse has moved outside the area of the content.
motion
The mouse cursor is always included in the video if it's moving, and for a short time after it stops moving.
never
The mouse cursor is never included in the shared video.
displaySurface

A ConstrainDOMString 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:

application
The stream contains all of the windows of the application chosen by the user rendered into the one video track.
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
A ConstrainBoolean 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.

规范

规范 状态 Comment
媒体捕获和流 候选推荐 初始定义。
MediaStream Image Capture 工作草案 Adds image constraints.

浏览器兼容性

更新 GitHub 上的兼容性数据
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
MediaTrackConstraints Chrome 59 Edge ≤18 Firefox Yes IE ? Opera 46 Safari ? WebView Android 59 Chrome Android Yes Firefox Android Yes Opera Android 43 Safari iOS ? Samsung Internet Android Yes
aspectRatio Chrome 59 Edge ≤79 Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 29 Opera Android ? Safari iOS ? Samsung Internet Android 7.0
autoGainControl Chrome Yes Edge ≤79 Firefox 55
55
46
Prefixed
Prefixed Implemented with the vendor prefix: moz
IE 不支持 No Opera Yes Safari ? WebView Android Yes Chrome Android Yes Firefox Android 55
55
46
Prefixed
Prefixed Implemented with the vendor prefix: moz
Opera Android ? Safari iOS ? Samsung Internet Android Yes
channelCount Chrome 59 Edge ≤79 Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 7.0
cursor Chrome 不支持 No Edge 不支持 No Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 不支持 No Chrome Android 不支持 No Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 不支持 No
deviceId Chrome 59 Edge ≤79 Firefox 36
注意事项
36
注意事项
Prior to Firefox 69, Firefox only supported deviceId in constraints passed into getUserMedia() .
IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 36
注意事项
36
注意事项
Firefox for Android only supports deviceId when used in constraints passed into getUserMedia() .
Opera Android ? Safari iOS ? Samsung Internet Android 7.0
displaySurface Chrome 不支持 No Edge 不支持 No Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 不支持 No Chrome Android 不支持 No Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 不支持 No
echoCancellation Chrome 59 Edge ≤79 Firefox 50 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 50 Opera Android ? Safari iOS ? Samsung Internet Android 7.0
facingMode Chrome 59 Edge ≤79 Firefox 50 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 50 Opera Android ? Safari iOS ? Samsung Internet Android 7.0
frameRate Chrome 59 Edge ≤79 Firefox 50 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 50 Opera Android ? Safari iOS ? Samsung Internet Android 7.0
groupId Chrome 59 Edge ≤79 Firefox 70 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 7.0
height Chrome 59 Edge ≤79 Firefox 50 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 50 Opera Android ? Safari iOS ? Samsung Internet Android 7.0
latency Chrome 59 Edge ≤79 Firefox 50 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 50 Opera Android ? Safari iOS ? Samsung Internet Android 7.0
logicalSurface Chrome 不支持 No Edge 不支持 No Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 不支持 No Chrome Android 不支持 No Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 不支持 No
noiseSuppression Chrome Yes Edge ≤79 Firefox 55
55
46
Prefixed
Prefixed Implemented with the vendor prefix: moz
IE 不支持 No Opera Yes Safari ? WebView Android Yes Chrome Android Yes Firefox Android 55
55
46
Prefixed
Prefixed Implemented with the vendor prefix: moz
Opera Android ? Safari iOS ? Samsung Internet Android Yes
sampleRate Chrome 59 Edge ≤79 Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 7.0
sampleSize Chrome 59 Edge ≤79 Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 7.0
volume
弃用 非标
Chrome 59 Edge ≤79 Firefox 不支持 No IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 不支持 No Opera Android ? Safari iOS ? Samsung Internet Android 7.0
width Chrome 59 Edge ≤79 Firefox 50 IE 不支持 No Opera Yes Safari ? WebView Android 59 Chrome Android 59 Firefox Android 50 Opera Android ? Safari iOS ? Samsung Internet Android 7.0

图例

完整支持
完整支持
不支持
不支持
兼容性未知
兼容性未知
非标。预期跨浏览器支持较差。
弃用。不要用于新网站。
弃用。不要用于新网站。
见实现注意事项。
要求使用供应商前缀或不同名称。
要求使用供应商前缀或不同名称。

另请参阅