The past 5 DVDs I've burnt work fine right until the end, and then, say the last .5GB of the disc, goes all blocky and won't play.
Would you guys say that the problem is my burner, or the DVDs I'm using?
Most likely your media.
What brand name/speed/and format?
How fast are you burning?
What programs are you using to rip/compress/and burn?
What is your burner name and model #?
Since these issues are at the end of your backup,Then reducing that backup target to about 4300 mbs should help.