What files or folders must be present on a blu-ray recorded disc, in order for it to work in a blu-ray player.
What exactly are you asking? The folders needed to make a Blu-ray disc compliant are BDMV and CERTIFICATE.
How come even though you put a BDMV and a CERTIFICATE folder on a DVD it shows as AVCHD and not BDMV with the BD disc? (PS3)
Blu-ray was built upon the AVCHD standard. AVCHD is a format largely developed by Sony for HD Camcorders. Blu-ray is an extension of that format which allows for things like subtitles, DTS audio etc. The PS3 simply tags it as an AVCHD as they are almost identical in structure, except that AVCHD was made to be put onto regular DVD optical media.