MP4 Video tags? (super slow)

I have an external drive with thousands of MP3 audio files. I can make changes to any of the tags on those files nearly instantly. I also have 300 MP4 movies on that same drive. The movies do not currently have any tag information filled out, which makes it a challenge when I want to watch a movie on my movie player, so I thought I would try using MP3Tag to add the title field. The movies are all relatively large - ranging in size from 125MB to 4GB.

When I tried adding a title tag, it took close to 5 minutes for it to save the change. I saw in the FAQ that it can be very slow when writing ID3V2, so I unchecked ID3V2 in the Options dialog and tried again in the hopes that it would only change the ID3V1 (I only need the Title Tag for these files).

It's just as slow (5:14 for the most recent change). Is there a trick to doing MP4 movies so that they save at a reasonable speed? Am I asking too much from MP3Tag? Right now I'm basically making a change to a single movie and walking away from the computer. At this rate it will take a month to add a title to all the movies.

AFAIK: As the tags have to be added to the file (in the front) and some housekeeping has to be done the file has to be rewritten - at least twice.
So if you treat a 4GB file, at least 8GB have to be transferred to and from your external drive....
How long does it take to copy such amounts of data? About 5 minutes?

Yes, anywhere from 3 to 7 minutes. If I run a batch convert on the whole directory overnight - something meaningless like filename to title, would I be able to edit these rapidly afterwards, or does it still have to rewrite the entire file?

I can't promise you anything. If the padding is big enough, then it may be possible just to write the tag bits.
And no: you can't set the padding.

I had this very same problem, i've got 400odd films on a NAS and although not ideal i have just begun moving them all to my laptop whilst i am at work and then when i get home i will do a batch run of them all (thanks to those that helped me with the scripting) and leave that running. for me i have then got to get my IMDB source working to get genre etc... for you, you could just move back, might be quicker to do that than do all the writing on the network drive?