I have a number of mp4 files to put on a DVD using architect. Some files drop right onto the timeline and others tell me it's the wrong format. I've rendered some in several sizes from 806x480 way down to 404x240 and still they don't drop in to the timeline. The files do play on my laptop so they are not corrupt.
These files were old Youtube videos I downloaded. I have a conversion program called "HD Converter Factory" and I found that if I converted the youtube files to mpg files and Architect accepts them. It's another stop but at least it works.