AudioTrackList.length

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范例
规范
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只读 AudioTrackList property length returns the number of entries in the AudioTrackList , each of which is an AudioTrack representing one audio track in the media element. A value of 0 indicates that there are no audio tracks in the media.

句法

var trackCount = AudioTrackList.length;

值

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

范例

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

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

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

规范

规范	状态	注释
HTML 实时标准 The definition of 'AudioTrackList.length' in that specification.	实时标准
HTML5 The definition of 'AudioTrackList.length' in that specification.	推荐

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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浏览器兼容性

图例

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