New installation of Suse 11.3, with a new build of the git repository Cinelerra-CV 4.1 from the http://cinelerra.org web site instructions.

Loaded a 5 second mpg file into Cinelerra, and then tried to play it back in both the viewer and the main window. It does decode the video and play it back, however, the playback speed is not smooth. It jumps, in what look like 1 second intervals, and then it gets really slow towards the end of the playback. By jumps, I mean that it is like the speed of playback is on a curve with bumps on each second. Since this is a new installtion of Cinelerra, it could be some settings that are off, as it has been some time since using Cinelerra.

For comparison, the same mpg file plays back fine in Kdenlive, although Kdenlive uses a much smaller playback screen...but it is nice and smooth in terms of playback speed. It also plays fine in Banshee.

I did take a look at the Cinelerra html manual, and there was a section on system adjustments that you can make...although I would like to find out what is causing it, and if it is a feature of the Cinelerra build?

Cinelerra have many bugs, it is one of them. Try to go the the preferences menu and switch to OpenGL, if it is OpenGL, then try something else. It may solve the problem, but cinelerra have hard time decoding big files. Mpeg2 are normally fine, bug DV and Raw suffer badly from this problem. It is why Cinelerra-CV is almost dead now (cleanup commit only in the past several months). The team is currently rewriting it completely, but it will take years.

Rewriting Cinelerra? Years?

I tried a small mpg file of about 10 seconds that plays in Totem fine without any jumps or stalls or any problems.