Storyline Video/,mp4 replacement - filename question...

Hi,

In order to maintain my required video quality, I was doing the Storyline "video replacement" switch - renaming the SL output .mp4 files to "xxx - old", and inserting replacements renamed to be the same. No videos worked when I played the course.... <BOO!>

I then noticed that the .mp4 file couplets had SLIGHTLY different naming conventions - I renamed all my files and everything worked as originally planned <HUZZAH!> I had created my batch earlier today, but had not changed the SL ones - but it decided to do a rename, changing all the "64s" to "128s".

I have (as yet) been unable to spot where these naming conventions are set, or why SL changes the name of something that I have not changed. Other slides had minor changes, but not the videos. So is it something that is changed at every publish. If so it is a bit of a surprise to me...

Please could someone explain any of this to me, as I need to think about workflow. It just seems to be an automatic process that I have no control over, but maybe I am missing something. The videos were all just .mov files converted to .mp4 using Freemake defaults.

Thanks