在此页

• 特性
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

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

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

groupId

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

Properties of audio tracks

autoGainControl

ConstrainBoolean object which specifies whether automatic gain control is preferred and/or required.

channelCount

ConstrainLong specifying the channel count or range of channel counts which are acceptable and/or required.

echoCancellation

ConstrainBoolean object specifying whether or not echo cancellation is preferred and/or required.

latency

ConstrainDouble specifying the latency or range of latencies which are acceptable and/or required.

noiseSuppression

ConstrainBoolean which specifies whether noise suppression is preferred and/or required.

sampleRate

ConstrainLong specifying the sample rate or range of sample rates which are acceptable and/or required.

sampleSize

ConstrainLong specifying the sample size or range of sample sizes which are acceptable and/or required.

volume

ConstrainDouble specifying the volume or range of volumes which are acceptable and/or required.

Properties of image tracks

whiteBalanceMode

字符串 specifying one of "none" , "manual" , "single-shot" ，或 "continuous" .

exposureMode

字符串 specifying one of "none" , "manual" , "single-shot" ，或 "continuous" .

focusMode

字符串 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

ConstrainDouble (a double-precision integer) specifying f-stop adjustment by up to ±3.

colorTemperature

ConstrainDouble (a double-precision integer) specifying a desired color temperature in degrees kelvin.

iso

ConstrainDouble (a double-precision integer) specifying a desired iso setting.

brightness

ConstrainDouble (a double-precision integer) specifying a desired brightness setting.

contrast

ConstrainDouble (a double-precision integer) specifying the degree of difference between light and dark.

saturation

ConstrainDouble (a double-precision integer) specifying the degree of color intensity.

sharpness

ConstrainDouble (a double-precision integer) specifying the intensity of edges.

focusDistance

ConstrainDouble (a double-precision integer) specifying distance to a focused object.

zoom

ConstrainDouble (a double-precision integer) specifying the desired focal length.

torch

布尔 defining whether the fill light is continuously connected, meaning it stays on as long as the track is active.

Properties of video tracks

aspectRatio

ConstrainDouble specifying the video aspect ratio or range of aspect ratios which are acceptable and/or required.

facingMode

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

frameRate

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

height

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

width

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

resizeMode

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 对象的 视频 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.

浏览器

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

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	注释
媒体捕获和流	候选推荐	初始定义。
MediaStream 图像捕获	工作草案	Adds image constraints.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	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

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

元数据

• 最后修改： Dec 23, 2019

相关话题

1. Media Streams API
2. MediaTrackConstraints
3. 特性

   1. aspectRatio
   2. autoGainControl
   3. channelCount
   4. cursor
   5. deviceId
   6. displaySurface
   7. echoCancellation
   8. facingMode
   9. frameRate
   10. groupId
   11. height
   12. latency
   13. logicalSurface
   14. noiseSuppression
   15. sampleRate
   16. sampleSize
   17. volume
   18. width
4. Related pages for Media Capture and Streams

   1. AudioStreamTrack
   2. BlobEvent
   3. CanvasCaptureMediaStream
   4. ConstrainBoolean
   5. ConstrainDOMString
   6. ConstrainDouble
   7. ConstrainLong
   8. DoubleRange
   9. HTMLCanvasElement.captureStream()
   10. LongRange
   11. MediaDevices
   12. MediaStream
   13. MediaStreamTrack
   14. MediaStreamTrackEvent
   15. MediaTrackCapabilities
   16. MediaTrackSettings
   17. MediaTrackSupportedConstraints
   18. Navigator.mediaDevices
   19. NavigatorUserMedia
   20. NavigatorUserMediaError
   21. VideoStreamTrack
   22. navigator.mediaDevices.getUserMedia()