I'm converting mp4 videos to webm with the following command: avconv -i INPUT.mp4 -c:v libvpx -qmin 10 -qmax 42 -maxrate 500k -bufsize 1000k -threads 2 -c:a libvorbis OUTPUT.webm Am I doing something wrong? Should I use all of these parameters? I just want to make the videos compatible with all the browsers/devices. The videos are not working on Firefox on most devices and on Chrome in a specific Android device that I have. EDIT: When i play the embeded videos on firefox, on any android device, it goes straight to the end and doesn't play. It only plays if i click in the progress bar. If i open the videos on firefox without embedding them in a html page, they seem to have a bigger width box outside then, while the video is inside it. I uploaded a video that i converted. Try it in firefox: https://mega.co.nz/#!cg9FVZJD!CpC6X3NXH8rAVdBiS9ZqqwyITdyPb_qkKAKsvQXRpzI This is a comparison between the videos, after and before the conversion: ![Image here]: http://i.imgur.com/V2FijCQ.jpg