导航器。媒体设备。getUserMedia视频质量和面临的模式约束

navigator.mediaDevices.getUserMedia({ audio: true, video: getConstraints(1280, 720) });

function getConstraints(videowidth, videoheight) {
    constraints = {
        facingMode: { exact: "environment" },
        width: { min: videowidth, ideal: videowidth, max: videowidth },
        height: { min: videoheight, ideal: videoheight, max: videoheight },
        frameRate: { min: 5, max: 8 }
    };
    return constraints;
}