[Bug 1323822] [NEW] Firefox can not play some WebM videos generated by avconv on Trusty

[Mossroy]

Public bug reported:

Steps to reproduce :
- Download the source H.264 video attached to this bug
- On a Trusty machine, convert this video to WebM with "avconv -i P5270914.MOV P5270914-trusty.webm". It should give the same result as attached
- Open this webm file in Totem or in VLC : it plays correctly
- Open this webm file in Firefox 29. When you click on play, it goes directly to the end and does not show anything
- Open this same webm file in Chromium (tested with version 34) : it plays correctly

If you generate the WebM file on Precise, with the same command-line, it plays correctly in Firefox (see attached P5270914-precise.webm).
So I suppose it comes from a difference in the way avconv does the conversion, that is not correctly supported by Firefox

All tests are made with Precise and Trusty amd64, with all current updates.
Firefox version 29.0 on both
avconv 9.13-0ubuntu0.14.04.1 on Trusty, and 0.8.10-0ubuntu0.12.04.1 on Precise

** Affects: firefox (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: trusty

** Attachment added: "Source video sample"
   https://bugs.launchpad.net/bugs/1323822/+attachment/4120893/+files/P5270914.MOV

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Title:
  Firefox can not play some WebM videos generated by avconv on Trusty

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