小程序中做一个canvas随着视频播放显示动画的效果，但是视频播放了，canvas中不会动。

queryVideo.fields({ context: true, size: true, rect: true, properties:['metadata'] }, videoRes => {
					const video = videoRes.context;
					const { width, height } = this.videoInfo;
					queryCvs.fields({ node: true, size: true }).exec(res => {
						const canvas = res[0].node;
						const ctx = canvas.getContext('2d');
						setInterval(() => {
							ctx.drawImage(video, 0, 0, width, height, 0, 0, canvas.width , canvas.height);
						}, 250

截图如下：上面的视频播放下面的canvas 一直定在第一帧不会动