Comment 15 for bug 1323822

Please note that this video has been generated with libav 9.13-0ubuntu0.14.04.1 on Ubuntu Trusty, by converting from a H.264 source video. It can be reproduced very easily with other source videos.
When converting with some other versions of libav (at least the one of Ubuntu Precise), or the latest version of ffmpeg, the generated video file can be played by Firefox.
See the details on Launchpad issue.

So it looks like a "misunderstanding" between this libav version and Firefox.
Maybe there is an issue in libav itself.
I created this issue on Buzilla because the video works on several other implementations, and because the issue is the same with Firefox on W7 (not ubuntu-specific)