Videos
It's 2016, MPEG-4/H.264 video format has won the battle, you can drop webm and ogv http://caniuse.com/#feat=mpeg4
Convert with AWS Elastic transcoder
The best way to do is integrate any player(like jwplayer) as the video tags are not supported by all browsers and convert all videos in one common format at time of upload as per your player support using any library like ffmpeg lib.
http://www.w3schools.com/html/html5_video.asp
Hello my client says their ad video must be in HTML5 format what does that mean? Is that a executable file only in browser or it's just a WebM format which can easily converted in third-party softwares. They send me a infographic video so I'm little confused is they're wanted a vector animated video which runs on website (like flash ad) or it's just a gif which we exporting as HTML format, Please help.