We rendered out several videos from After Effects using the MPEG-4 preset. The resulting files do not play in Quicktime (Mountain Lion) or other QT-based apps like iTunes; they only play properly in apps like VLC, MPlayer, Streamclip, etc. They also play fine in Quicktime on a PC.
What is it with these mp4s that makes them incompatible with Quicktime? Or is this a Quicktime bug?
Tell you what: find a machine that does NOT have QT X installed on it. Try for a machine with QT 7 installed. Try playing the file on it and see what happens.
QTX was definitely NOT Apple's premiere effort in the media container world. It pretty much stinks.
Yes they will play in QT7 (though not full res – they look awful) but that doesn't help me here. Client has QTX, have to make that work.
Then render out in a Lossless codec like QT's PNG codec (not the image sequence), and then spend 35 bucks to get QT Pro for that God-Awful X version. Export to something within it.