Function handleSourceOpen

src/core/background.ts:88–92

(event)

 * 调用MediaSourceBuffer::addSourceBuffer方法来   ==>  构建一个存放视频数据的Buffer；
 */
function handleSourceOpen(event) {
    trace('MediaSource opened！');
    sourceBuffer = mediaSource.addSourceBuffer("video/webm;codecs='vp8'");
    trace(sourceBuffer);
}

/* 这里把每10ms获取的数据放入recordedBlobs */
function handleDataAvailable(event) {