opencv_ffmpeg2413_64.dll gets loaded, VideoCapture still cannot open files

I'm compiling using VS 2015, and I can see in the debug log that the ffmpeg dll gets properly loaded, but when I try to open a file using `VideoCapture` (`VideoCapture::isOpened()` returns false). I do have ffmpeg and the K-Lite codec pack installed, and I'm trying to open a H.264 (mp4) or an XviD (avi) file, no dice. Thanks in advance!