We would need to see the settings that you use to create the MP4. Post a screenshot if you can. and then a Mediainfo report of one of the MP4s that will not play.
It's the default codec settings for an "internet" mp4 in every case.
And here's what Windows says is the resulting file:
It seems you don't have a Codec to play an MP4, which is odd, but I have seen odder. You might try downloading and installing VLC. It will play anything.
I did. It does. I also downloaded a codec pack and that fixed it. Not sure why there wasn't a codex there, but it is fixed now.
Time to change the title of this thread to "[Resolved]Can't make a working MP4 file".Isn't it cspvideo?
Just a reminder/warning regarding codec packs in this FAQ (item 12. Codec packs - last resort only).(Also here, 2nd paragraph)