DnevnoySwet friend, I believe the video was not inserted because it can cause problems on some PCs, since they are not a single platform like a raspberry Pi, which is always the same ...
However, as you want to test, I recommend watching videos on YouTube where you are taught how to put videos in the Recalbox / Batocera intro .....
I think you should just get the MP4 video that is here in the forum (or another of your choice) and insert it in the Boot folder, in the same place where the raspberry is ... there are videos on youtube showing this, but in fact I never tried ....