12.04 LTS

It appears that ffmpeg no longer works properly in this release for converting recordmydesktop's .ogv recordings to WebM. As it is no longer maintained, it's recommended to use its replacement avconv instead, provided in the libav-tools package (which seems to be automatically installed if ffmpeg was installed).

The command needed to use avconv for conversions is not too much different than from ffmpeg:

avconv -i input.ogv output.webm

Thus, if anybody's facing the same issue of trying to use only free packages to convert from .ogv to .webm in 12.04 (or presumably later), this is how I resolved it. This should be helpful if you're making recordings to show new features or document issues using video.

Webm has to first be supported out the box in the correct gstreamer packages before it can be supported in Ubuntu out the box. The main reason it is not included as yet is because it is a rather "recent" format and code for supporting it is still a bit fresh.

You would have to wait for gstreamer to support it as part of their default set, since at the moment it's still a bit "experimental" in gstreamer.