I used to be able to render to H.264 fine, but ever since I made a video with an mp3 as the soundtrack, H.264 (and even mp4) render in HORRIBLE quality. All the titles and video are super pixelated. Anyone know what could of caused this or what I can do to fix it? Thanks!

it's libx264 bug
http://kdenlive.org/forum/h264-renders-unusually-slowly-unusually-large-file-size-and-echo-078-ubuntu-1010

it should be fixed in the latest version, just update your system ;)

I'm guessing you mean just do an update through the update manager? I did that and I still get the same problem. I tried rendering in openshot and the it came out fine. The files aren't large and it's not unreasonably slow, it just looks super pixelated and bad.