I'm rather new with AE but I've managed to create a really cool looking sun and I wanted it animated as my desktop background. I understand .MWV and .MPEG is the standard formats for dreamscenes however I can't for the life of me get MPEG to render and .MWV comes out way too pixelated. How the heck do I get MPEG to render?! I have the composition set to 1920/1080P at 29.97 frame rate. I use these same settings in the rendering but it still says It doesn't match.
If you're on CS3 or CS4 first be sure your composition is set to HDTV 1920x1080 29.97fps by selecting the "HDTV 1080 29.97" preset in the Composition Settings.
Then for the render open the Output Module settings and choose the "MPEG2 Blu-ray" preset. It will render out 4 files: the movie, the audio and two other files you probably won't need. If you just need the video then you can delete the other files including the audio.
I'm not familiar with Dreamscapes but if it doesn't like the MPEG Blu-ray file then you may have to change the extension to .mpg instead of the default .m2v. Our broadcast server likes the files, just not the .m2v extension, so we always change it to .mpg and it works fine.