I have a dvd that was burned from a cam recording of a play we did. The guy was supposed to burn it to a single dvd. It’s on 5. It’s only about 2 1/2 hours. When I tried to watch them on my computer and it says “Windows Media Player cannot play this DVD because a compatible DVD decoder is not installed on your computer”. Also, I want to convert these files so they will all fit on one dvd. Any help here? The files are video_ts.bup, .vob, and .ifo. Thanks. 
Here is the solution for you.
1. Convert these DVDs to MPEG files with Alive DVD Ripper.
http://www.alivemedia.net/dvd-ripper/index.htm
2. Join the converted MPEG files into one large MPEG file with Alive Video Joiner.
http://www.alivemedia.net/videojoiner/index.htm
3. Burn the large MPEG into a DVD
If you means you have DVD folder contain AUDIO_TS and VIDEO_TS folder,and VIDEO_TS folder contail .vob,two bup and two ifo file,why don’t you burn to dvd disc directly?
But I guess it’s a codec problem.Good luck