I recently tried it on another file and it worked as well.
On another note, I'm not sure whether it's appropriate or not to ask this here but here I go anyways:
The mp4 files obs generates still have very strange/obvious audio/video desync issues (almost 1 second delay on the audio). I tried playing it back in windows media player, vlc, sony vegas and uploaded a clip onto youtube and the problem was present everywhere. I thought it might fit in here since the topic is faulty mp4 files but I can open another thread if it doesn't make much sense, too.
So even files remuxed with FFmpeg are failing? I'm beginning to suspect something might be going on with VLC, though I'm not entirely sure. However, if FFmpeg-muxed files don't work then it's definitely indicative of something wrong with the player, though I just couldn't say for sure yet.
There really should be nothing wrong with the files that would cause it to happen, outside of the files just being very large and requiring large integers. Again, if you are not using VLC 64bit you will run in to problems.
mp4 is a pain. I recommend use mkv with FFmpeg. MP4 conversion can be added as a tool in OBS. Also using matroska container allows to add more format for audio like lossless code FLAC or ALAC. Of course all is for local recordings.
I could not play some long files with anything, the one i had a problem with today was ~600MB, but a bit over an hour and a half long from doing a stream (540p30, x264 med preset, 750kbit cbr on video, + audio) for a friend. 64 bit of VLC plays it fine, thanks (: