changed:
-
The movie formats GEM can handle (still) depend on the platform you are using.

On Windoze you can read all AVI-files you have codecs for

On linux the readable formats depend on the libraries you had installed when you compiled GEM. 
Currently there is (optional) support for AVI, quicktime (*.MOV) and MPEG (*.MPG) files. 
Not all quicktime-formats are supported. This is unfortunate but is due to linux restrictions. 
I highly recommend that you install the mpeg3-library from Heroine because it is much more stable than mpeg1 (which comes with many linux-distributions). 
If you have compiled in support for libavifile, you will be able to open Micro$oft-AVI-files. 
If you have installed the proper codecs (libavifile supports a mechanism for loading codecs from windows-DLLs) you should be able to open almost any format. 
If you have serious problems, mail them to me. (Be ready to upload the movie-file that won't work) 

On Mac os-X, just any format supported by that platform (this is basically !QuickTime) should work fine.