Could you please try to explain exactly what happens ? Are the movie showing or not ? In a separate window or in the game ? Are you running the game fullscreen or windowed ? You say mpeg2dec "helped": in what way ? Was it not showing before and now it is ? You say it helped "until switching resolution": what worked differently after changing resolution ? What was the original (working) resolution and the later resolution that didn't work ? You know you can't change any setting, including resolution, while the game is running, right ?
WCP set to work in full-screen. "Standard" (non-DVD) movies showed fine, in full-screen, with both audio & video parts. Initial resolution for HiRes set to 1280x720. DVD movies resulted as silent full-screen black box, no video, no audio, with correct timing of original movie length, then game continue in set resolution. It look like that K-Lite codec pack has compatible ac3 codec, coz after its installation DVD movies resulted as still black box but having correct audio part. K-Lite has few switchable MPEG2 engines according to it information but it does not help to get video part of DVD movies, blank (black) screen instead of it. Manual installation of mpeg2dec solves the problem for period of time. DVD movies showed as expected - full-screen, video and audio, even with correct subtitles. But when I switch resolution for HiRes to 1920x1080 than video part of DVD movies are lost again, welcome back good old black box screen. Switching back to 1280x720 does not help anymore. Reinstalling mpeg2dec does not help anymore.
PS. Got Your tip for WCSO. Thanks.