1. Put the .sdm file in your demos folder.
2. Run Soldat with the -demo parameter.
freecam (no/yes) - the user can freely change the camera (default no)
speed (0-...%)- how quick the playback will be specified in percents (default 100%)
notexts (no/yes) - no texts, menus or cursor will be displayed during playback (default no)
extract (no/yes) - extracts the demo to BMP files (default no). Later they can be used to make an AVI file in a program like "Bmp2Avi".
Where it says yes/no, replace with 1/0 respectively.
For instance, to extract a demo file, I would run soldat with the parameter
-demo 0 100 1 1
Then use BMP2AVI to make a movie file. You could also use Audacity to record the sound from it.