The reasons a dvd might not play in your home set-top player is multiple:
* Burnt at too high a speed, __ * Your player doesn't support DVD R disks, __ * Your player only supports DVD-R or DVD+R but not both, __ * you encoded the video & audio at too high an overall bit rate (max. should be kept below 9 Mbps), __ * your settings for burning were inapproprate (Data disk instead of video dvd (UDF format)), __ * the program you used to convert did a horrible job, __ * the brand of dvd disk you used is cheap & unreliable, __ * some dvd players are brand specific & don't perform well if at all with some brands of dvd disks, __ * your burner doesn't properly support a particular brand of disk.

There's probably more possible reasons but these are the ones I can think of off the top of my head.