The problem of setting? You didn't say the specific model, and you can't specify it.

Go and see if there are any settings. There are settings to save the progress. Look carefully.

If not, I suggest that you divide the document into several or more than ten copies when copying to mp4 in the future.

So you can see the difference next time you watch it.

It's convenient for the computer to divide files, just cut and paste them.