An OGM file is a container. Inside it can contain a video track (codified with any codec) and one or more audio tracks (with their respective codec).
It's like an AVI: AVI is not a compression codec, it's a container. It can have inside some video on Xvid, DivX, MPEG, MJPEG, Theora, Indeo, etc., and sound on MP3, PCM, Vorbis, etc. It can even have no sound. So, OGM is the same type of thing as AVI, but it's better and is a free and open format, too.
Although you can use any codec, it's very common to distribute OGM files using these ones:
Video: Theora
Audio: Vorbis
Furthermore, OGM can contain subtitles and more; see the Wikipedia: OGM.
On Linux, almost any player works. Mplayer, xine, vlc, ...
On Windows, I'm not sure. vlc should work, it can open almost any type of file. And it's said that bsplayer opens them too.
On MacOS, I'm not sure. But surely vlc will also work.
On BSD, vlc too.
I have recorded some videos with my digital camera BENQ DC S40, which creates them in ASF format and with a very low quality. ASF is not an open format (and that DOES matter) and is difficult to play and handle.
I convert the videos to OGM Theora+Vorbis, which are free/open codecs and technically very good and easy to handle. Being free allows any programmer to support them on their programs without any problem.
To convert an ASF to OGM I use the vlc player
(Video Lan Client), which opens a wide range of formats, and also transforms and does streaming from files.
It can be done under the menu File -> Open,
but I use this command (Linux):
vlc source_file.asf --sout
"#transcode{vcodec=theo,vb=1024,scale=1, acodec=vorb,ab=192,channels=2}
:duplicate{dst=std{access=file, mux=ogg,url='/home/usuario/destination.ogm'}}"My videos have extremely poor quality (the camera is not a good one, and they come from an ASF), but on the Internet you will find normal OGMs with very good quality and small file size. Search also on eDonkey or P2P networks.
If you have audio files on MP3, try compressing them with the Vorbis codec (it produces files with OGG extension). The file size will be almost half the original one, without losing quality. I have all of them like this.
24-1-2005 Daniel Clemente Laboreo. http://www.danielclemente.com/ , n142857_at_gmail.com