VideoTrackList.length

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句法
范例
规范
浏览器兼容性
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只读 VideoTrackList property length returns the number of entries in the VideoTrackList , each of which is a VideoTrack representing one video track in the media element. A value of 0 indicates that there are no video tracks in the media.

句法

var trackCount = VideoTrackList.length;

值

A number indicating how many video tracks are included in the VideoTrackList . Each track can be accessed by treating the VideoTrackList as an array of objects of type VideoTrack .

范例

This snippet gets the number of video tracks in the first <video> element found in the DOM by querySelector() .

var videoElem = document.querySelector("video");
var numVideoTracks = 0;
if (videoElem.videoTracks) {
  numVideoTracks = videoElem.videoTracks.length;
}

Note that this sample checks to be sure HTMLMediaElement.videoTracks is defined, to avoid failing on browsers without support for VideoTrack .

规范

规范	状态	注释
HTML 实时标准 The definition of 'VideoTrackList: length' in that specification.	实时标准

浏览器兼容性

The compatibility table in 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
`length`	Chrome 45 Disabled 45 Disabled Disabled From version 45: this feature is behind the `enable-experimental-web-platform-features` preference (needs to be set to `enabled` ). To change preferences in Chrome, visit chrome://flags.	Edge 79 Disabled 79 Disabled Disabled From version 79: this feature is behind the `enable-experimental-web-platform-features` preference (needs to be set to `enabled` ). 不支持 12 — 79	Firefox 33	IE 10	Opera 32 Disabled 32 Disabled Disabled From version 32: this feature is behind the `enable-experimental-web-platform-features` preference (needs to be set to `enabled` ).	Safari 6.1	WebView Android 45	Chrome Android 45 Disabled 45 Disabled Disabled From version 45: this feature is behind the `enable-experimental-web-platform-features` preference (needs to be set to `enabled` ). To change preferences in Chrome, visit chrome://flags.	Firefox Android 33	Opera Android 32 Disabled 32 Disabled Disabled From version 32: this feature is behind the `enable-experimental-web-platform-features` preference (needs to be set to `enabled` ).	Safari iOS 7	Samsung Internet Android No

图例

完整支持
不支持
用户必须明确启用此特征。

元数据

最后修改： Mar 18, 2019

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句法

值

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规范

浏览器兼容性

图例

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