In order to use HTML5 video and support all modern browsers, you need to serve (as of the time of writing) 2 different source encodings: mp4 and webm. The mp4 format is commonly used in desktop media, and can be easily be encoded with programs like Handbrake. The webm format is not as commonly found. I tried the free Mira video conversion software, however it doesn't allow you to tweak any settings. On the other end of the spectrum, ffmpeg is a command-line tool that gives you full control over everything (which can be a little overwhelming at first). Here's how I went about encoding my webm video file with ffmpeg.