dvd burning problem. Burner or Media?

[spigen]

I dont really know, but i recently bought some more blank Ritek DVDs and starting to burn my movies like usually. Well tonight i noticed on the writing side after i burned a movie these weird circular marks, like it burned to deep or something. so i looked at the rest of the movies i burned in the past couple weeks and they all have these weird marks. So then i take a pile of movies and put them in the dvd player. Some load up and some don't. Some play but freeze i guess once they reach the areas with the weird marks.

Note:
- the marks are not scratches
- no errors
- burn completes

So my question, since i have burned over 800 dvds plus who knows how many cd on my Plextor PX-708A burner...is it going bad. Or is the 50 bundle of Ritek blank dvds defective?