从摄像头获取stream对象并导入页面上的video元素这个过程并不简单，仅就这一话题就可以写一整本关于C或C++的书！--《Learning webrtc中文版》
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Document</title> </head> <body> <video id="v1" autoplay controls></video> </body> <script> function aaa() { var userMedia = navigator.mediaDevices.getUserMedia({ audio: false, video: true }).then(mediaStream => { console.log("coming in...") document.getElementById(‘v1‘).srcObject = mediaStream; }).catch(err => { console.log("coming in.4..") console.log(err) }) } window.onload = function () { aaa(); } </script> </html>
Here‘s an example of using navigator.mediaDevices.getUserMedia(), with a polyfill to cope with older browsers. Note that this polyfill does not correct for legacy differences in constraints syntax, which means constraints won‘t work well across browsers. It is recommended to use the adapter.js polyfill instead, which does handle constraints.
// Older browsers might not implement mediaDevices at all, so we set an empty object first
if (navigator.mediaDevices === undefined) {
navigator.mediaDevices = {};
}
// Some browsers partially implement mediaDevices. We can‘t just assign an object
// with getUserMedia as it would overwrite existing properties.
// Here, we will just add the getUserMedia property if it‘s missing.
if (navigator.mediaDevices.getUserMedia === undefined) {
navigator.mediaDevices.getUserMedia = function(constraints) {
// First get ahold of the legacy getUserMedia, if present
var getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
// Some browsers just don‘t implement it - return a rejected promise with an error
// to keep a consistent interface
if (!getUserMedia) {
return Promise.reject(new Error(‘getUserMedia is not implemented in this browser‘));
}
// Otherwise, wrap the call to the old navigator.getUserMedia with a Promise
return new Promise(function(resolve, reject) {
getUserMedia.call(navigator, constraints, resolve, reject);
});
}
}
navigator.mediaDevices.getUserMedia({ audio: true, video: true })
.then(function(stream) {
var video = document.querySelector(‘video‘);
// Older browsers may not have srcObject
if ("srcObject" in video) {
video.srcObject = stream;
} else {
// Avoid using this in new browsers, as it is going away.
video.src = window.URL.createObjectURL(stream);
}
video.onloadedmetadata = function(e) {
video.play();
};
})
.catch(function(err) {
console.log(err.name + ": " + err.message);
});
https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia
var promise = navigator.mediaDevices.getUserMedia(constraints);
constraintsA MediaStreamConstraints object specifying the types of media to request, along with any requirements for each type.
The constraints parameter is a MediaStreamConstraints object with two members: video and audio, describing the media types requested. Either or both must be specified. If the browser cannot find all media tracks with the specified types that meet the constraints given, then the returned promise is rejected with NotFoundError.
https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamConstraints
Some combination—but not necessarily all—of the following properties will exist on the object.
audioMediaTrackConstraints object providing the constraints which must be met by the audio track included in the returned MediaStream. If constraints are specified, an audio track is inherently requested.videoMediaTrackConstraints object providing the constraints which must be met by the video track included in the returned MediaStream. If constraints are specified, a video track is inherently requested.
video的选项
https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamConstraints/video
var videoConstraints = true | false | MediaTrackConstraints;
MediaTrackConstraints的选项
https://developer.mozilla.org/en-US/docs/Web/API/MediaTrackConstraints
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.
Some combination—but not necessarily all—of the following properties will exist on the object.
deviceIdConstrainDOMString object specifying a device ID or an array of device IDs which are acceptable and/or required.groupIdConstrainDOMString object specifying a group ID or an array of group IDs which are acceptable and/or required.autoGainControlConstrainBoolean object which specifies whether automatic gain control is preferred and/or required.channelCountConstrainLong specifying the channel count or range of channel counts which are acceptable and/or required.echoCancellationConstrainBoolean object specifying whether or not echo cancellation is preferred and/or required.latencyConstrainDouble specifying the latency or range of latencies which are acceptable and/or required.noiseSuppressionConstrainBoolean which specifies whether noise suppression is preferred and/or required.sampleRateConstrainLong specifying the sample rate or range of sample rates which are acceptable and/or required.sampleSizeConstrainLong specifying the sample size or range of sample sizes which are acceptable and/or required.volumeConstrainDouble specifying the volume or range of volumes which are acceptable and/or required.whiteBalanceModeString specifying one of "none", "manual", "single-shot", or "continuous".exposureModeString specifying one of "none", "manual", "single-shot", or "continuous".focusModeString specifying one of "none", "manual", "single-shot", or "continuous".pointsOfInterestexposureCompensationConstrainDouble (a double-precision integer) specifying f-stop adjustment by up to ±3. colorTemperatureConstrainDouble (a double-precision integer) specifying a desired color temperature in degrees kelvin.isoConstrainDouble (a double-precision integer) specifying a desired iso setting.brightnessConstrainDouble (a double-precision integer) specifying a desired brightness setting.contrastConstrainDouble (a double-precision integer) specifying the degree of difference between light and dark.saturationConstrainDouble (a double-precision integer) specifying the degree of color intensity.sharpnessConstrainDouble (a double-precision integer) specifying the intensity of edges.focusDistanceConstrainDouble (a double-precision integer) specifying distance to a focused object.zoomConstrainDouble (a double-precision integer) specifying the desired focal length.torchBoolean defining whether the fill light is continuously connected, meaning it stays on as long as the track is active.aspectRatioConstrainDouble specifying the video aspect ratio or range of aspect ratios which are acceptable and/or required.facingModeConstrainDOMString object specifying a facing or an array of facings which are acceptable and/or required.frameRateConstrainDouble specifying the frame rate or range of frame rates which are acceptable and/or required.heightConstrainLong specifying the video height or range of heights which are acceptable and/or required.widthConstrainLong specifying the video width or range of widths which are acceptable and/or required.resizeModeConstrainDOMString 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. nonemeans 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.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.
cursorA 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.
alwaysmotionneverdisplaySurfaceA 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:
applicationbrowsermonitorwindowlogicalSurfaceConstrainBoolean 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.| Specification | Status | Comment |
|---|---|---|
| Media Capture and Streams | Candidate Recommendation | Initial definition. |
| MediaStream Image Capture | Working Draft | Adds image constraints. |
| Unknown | Unknown | Added properties for screen sharing. |
原文：https://www.cnblogs.com/yasepix/p/10929931.html