The height and wight attributes of the html5 video tag define the size of the video, but do not define the poster size passed?

  html5, question

If you define the height of video: 200pxwidth: 100%; The video is this size, but the picture is not this size. Is the picture size very irregular when the video is loaded?

Poster pictures are scaled according to the size of your video. Only the preload property needs to be changed to none. Without preloading the video, the poster picture will not know the size of the video you want to play and will not be scaled.