.mkv vs .mp4 file tag write speed

I have been using ffmpeg to change the video container from .mkv to .mp4 format. But today I left them as .mkv files and i was amazed how fast MP3TAG wrote the filename to title tag. I mean it would take minutes to write a few tags to taking a few seconds to write 26 tags out.

Is it normal for the .mp4 formated files to take so long and .mkv to write out so fast. This was all on the same SSD drive so no difference in I/O performance.

Thanks, Bill

It depends on the size of the file and how much free space is available in the file to perform the changes. If the file is large and a rewrite is necessary, it usually takes a while.