capture属性放input file文件上传控件上，可以给它一个值“user”或“environment”。user启用用户的后置摄像头和/或麦克风，environment启用用户的前置摄像头和/或麦克风。
<p>
<label for="soundFile">What does your voice sound like?:</label>
<input type="file" id="soundFile" capture="user" accept="audio/*" />
</p>
<p>
<label for="videoFile">Upload a video:</label>
<input type="file" id="videoFile" capture="environment" accept="video/*" />
</p>
<p>
<label for="imageFile">Upload a photo of yourself:</label>
<input type="file" id="imageFile" capture="user" accept="image/*" />
</p>
