Now we have a convenient way to convert multimedia in Ubuntu. It is Selene, a GUI tool to help us convert many audios and videos. Here some instructions about how to convert audio and then video with Selene. If you didn't have Selene yet, follow our how to install Selene article.
We will convert OGG to MP3. Open Selene > Add Files > select presets from Folder field > select MP3 Audio (.mp3) from Preset field > press Start button > wait until it is finished. We use OGG file from some audio resource/podcast sites.
We will convert OGV to MP4. Open Selene > Add Files > select presets from Folder field > select MP4 Video (mp4 h264 aac) > press Start button > wait until it is finished. We use OGV file from some Linux screencasting sites.