问题
I am using video HTML tag. So far, if I am NOT specifying any poster, how one will be selected? Does it depend on video file format? Does it depend on video content (first frame etc)? Does it depend on a mobile browser version etc?
回答1:
So far I've only ever used MP4 files with the video tag and each time I've not specified a poster image. It has picked up the first frame by default.
I know this information doesn't have any concrete evidence for you and may not help but thought I would share my experience.
来源：https://stackoverflow.com/questions/14448797/video-poster-without-poster-attribute-mobile-browsers