.mp4 Video

Sorry if this is a dumb question (I didn't find anything with a quick search, which may be my answer).

I have a Canon sx280 IS that records movie files as .mp4. When saved in a folder with photos, or uploaded to a photo service, they do not sort correctly. It appears the camera does not assign a Media Created date. I have tried many EXIF editors for photos, none work.

Is it possible to alter tag data in a .mp4 movie file with MP3Tag? Any recommendations?

Thanks

Have you tried it?
MP4 files are loaded by MP3tag - and it should be possible to modify tags.
Here you find a list of possible fields: http://help.mp3tag.de/main_tags.html

Yes, I tried. Does anyone know if this is possible?

I don't really understand the question: if you have tried to modify tags of MP4 files with MP3tag, you should see the effect immediately. Some MP4 files have a special structure and they don't work.
Perhaps a look at also this thread sheds more light on it: /t/14151/1