I was given a DVD-RW that had 2 videos on it, which couldn't be read by ordinary DVD players, but I could see files on it when put in the Mac. My challenge was to get the videos playable on an ordinary DVD. Research in wikipedia showed it was written in DVD-VR format, which allows for changes in content once written, but isn't understood by most domestic players. Instead of VOB files, which can often be treated as MPEG-2 files by just changing their extension, it has a single VR_MANGR.IFO (small; metadata) and a VR_MOVIE.VRO (large; audio + video data) inside an DVD-RTAV directory.
Video is recorded as an MPEG-2 program stream. Video resolution depends on the recording quality and the video format used. Multiple audio encodings are allowed including MPEG Audio, Dolby AC3 and Linear PCM.
Not much video software appears to read this format: on the Mac iDVD and iMovie both don't, but MPEG Streamclip, AVS Video Converter, DVDxDV and VisualHub do. I tried MPEG Streamclip and it doesn't understand the IFO files, but it does read the VRO ones. It got me very confused for a while, as it was only finding one of the 2 videos, despite reporting the full 1.5GB worth of file. But some fiddling in the options to fix timecode breaks, made it possible to find the second file. However, exporting it out as an MPEG-2 file doesn't seem to work for iDVD, despite this being what DVD Video format uses. Humph. Next step is to try QuickTime, this being an Apple product. This produces 2.8 GB for 23 minutes. I also tried DV format (5GB). Shame since the MPEG-2 was only 700MB. And, as expected, there's a very long transcoding process (130 minutes elapsed for the 100 minutes of video). Frustrating!(For Windows machines, the DVD FAQ Q4.10 (~2005 vintage) notes: "use Heuris Extractor or Panasonic DVD-MovieAlbum to copy them to a hard disk in usable format. Alternatively you can use DVD disc creation software such as InterVideo WinDVD Creator, MedioStream neoDVD, or Sonic MyDVD can import from -VR discs and write out standard DVD-Video discs.")