Similar to what delt31 said, I ran into a few issues immediately upon implementing a single video change in JP 1.02 (using PB 7.56). The file I was importing was an H.264 .mp4 converted from a .mov file. All I did was add some overlay text/graphics to the existing video that I had exported from PB to edit, then bounced that version of the video to a new .mp4.
Issue 1: Video did not seem to import when testing on my JP pin. The stock video was still playing.
Cause: In the Videos tab I located the video I wanted to replace. There were two nearly identical locations JawsIntroToIsland_Title and JawsIntroToIsland_Title_NoText. The issue is that PB wasn't actually honoring the video location I was at. I would type in and let PB autofill the location name and hit enter. While it appeared I was at that video location (which are 0x60 and 0x61), it kept showing that I was at location 0x0. So when I was importing manually I was unknowingly importing my video to the 0x0 location over and over again.
Solution: Start over with a fresh code version. Then I kept having to quit and restart PB to make sure that when I hit enter, I was actually looking at and importing to the right location. I can consistently reproduce this. Here's a screenshot. Note that it shows 0x0 when it should be showing 0x60. Trying to select another location from the dropdown list also results in me staying at 0x0 BTW.
Issue 2: Videos tab > Import Video option appears to be broken. Any time I use that option to import a video file I get a nasty null reference exception (sorry I don't have a screenshot of that as reproing it corrupts the firmware file = Issue 3).
Solution: Only use the Import file (no conversion) option instead. However, this also resulted in an error if I tried to import the same .mp4 file to the other location JawsIntroToIsland_Title_NoText after I had just imported it without error to JawsIntroToIsland_Title.
Issue 3: Upon any given, seemingly successful flash of the new firmware the pin wouldn't load up. Instead it would show the JP logo, then say "game restarting..." over and over in a loop.
Cause: Not entirely sure. I feel like each time this happened was after I got some kind of Issue 2 error in PB which was corrupting the firmware.
Solution: Start over and try again. If you don't get any errors upon importing video files the resulting firmware should load up correctly.
Perhaps, overall the safer bet is to use macros instead of manual UI importing for videos? Not trying to knock this feature whatsoever, it's amazing. Just wanted to provide some input for possible bug fixes and to help others running into the same.