[TOC] ## MediaStream ***** 一些方法 ``` 流媒體里添加軌：MediaStream.addTrack() 流媒體里刪除軌：MediaStream.removeTrack() 在流媒體里獲取視頻軌：MediaStream.getVideoTracks() 所有音頻軌：MediaStream.getAudioTracks() ``` Media事件 ``` MediaStream.onaddtrack MediaStream.onremovetrack MediaStream.onended ``` ## 獲取視頻約束 創建一個div用來存放獲取到的視頻約束參數： ``` <div id="constraints" class="output"> </div> ``` 獲取該div元素 ``` var divConstraints = document.querySelector('div#constraints'); ``` 在gotMediaStream函數里添加 ``` function gotMediaStream(stream) { vidoeplay.srcObject = stream; var videoTrack = stream.getVideoTracks()[0]; var videoContraints = videoTrack.getSettings(); // 獲取video所有的約束 divConstraints.textContent = JSON.stringify(videoContraints, null, 2); return navigator.mediaDevices.enumerateDevices(); } ```