For this to be resolved in Ubuntu 12.04 LTS, an appropriate fix needs to be written for libav 0.8. Updating to a newer libav isn't an option as the API has changed and that would break compatibility with all the software using libav in the archive. Once a fix has been written, Mozilla would then need to unblock libav in Firefox.
This is unlikely to happen before 12.04.5 LTS reaches end of life in a few weeks.
I recommend updating to a newer Ubuntu release, such as 14.04 LTS, or preferably 16.04 LTS now if this is an important issue rather than waiting until the end of life of 12.04 LTS in a few weeks.
For this to be resolved in Ubuntu 12.04 LTS, an appropriate fix needs to be written for libav 0.8. Updating to a newer libav isn't an option as the API has changed and that would break compatibility with all the software using libav in the archive. Once a fix has been written, Mozilla would then need to unblock libav in Firefox.
This is unlikely to happen before 12.04.5 LTS reaches end of life in a few weeks.
I recommend updating to a newer Ubuntu release, such as 14.04 LTS, or preferably 16.04 LTS now if this is an important issue rather than waiting until the end of life of 12.04 LTS in a few weeks.