const video = document.getElementById('video');
const canvas = document.createElement("canvas");
const canvasCtx = canvas.getContext("2d")

const ratio = window.devicePixelRatio || 1;
canvasCtx.scale(ratio, ratio);

// canvas大小与图片大小保持一致，截图没有多余
canvas.width = video.offsetWidth * ratio;
canvas.height = video.offsetHeight * ratio;

canvasCtx.drawImage(video, 0, 0, canvas.width, canvas.height)
const imgBase64 = canvas.toDataURL("image/png");