@dankcushions thank you for your suggestions and you're right. I've tried to change the gpu_mem but it still crash, just after a different number of exiting game.
So if there's no solution I tried a workaround, hope this could be useful to someone else. Not using Omxplayer I had that problem with some video preview that got sound but not video. As I told you before I noticed the problem was the codec profile. The lucky thing is that on W10 the thumbnails of videos (associated to VLC program) that have this issue show the VLC icon instead of the screenshot preview of the video so they were easily recognizable. I used a program (WinXHDVideoConverterDeluxe) to convert manually those videos (they were more than one thousand but the program runs fast e you can upload and launch them all togheter and just wait, the only boring thing was to select them all manually). I replaced the codec profile corrected videos and everything works fine. I made two tests of almost 4 hours and exactly 250 exiting game (but who counts, I'm going crazy, I know) each one and the issue didn't occurred.
The only thing that I noticed is that shutting down the system it took about 20 seconds of black screen before starting the power off process, technically why? Did I stress to much the system? And what do you thing, should I expect another crash somehow or maybe I'm safe?
Thank you so much.