The UK TV station "Dave" has, after many years, resurrected the Sci Fi comedy show "Red Dwarf" for three special episodes. I tried to record the first episode on my set top DVD recorder. Unfortunately the blank disk I used appeared to be faulty, and upon trying to finalise the disk it failed miserably, and I was left with an apparently unreadable disk.

 Some research on the internet lead me to this web page :-
 http://riplinton.blogspot.com/2008/04/using-gnulinux-tools-to-recover-dvd.html

I'll cut-n-paste bits from that web page, and add a few more notes of my own to show the steps I used to recover video from my failed DVD recording. I skipped a few bits and my results were not perfect, but it did work ! I would recommend reading the original web page for the full procedure.

The first step is to use a program that was new to me, but one I had heard of previously. It is called dvdisaster, and it seems to be e highly useful bit of software that can read raw data of a CD or DVD disk, and store the result in one .iso file on your hard disk. As dvdisaster slowly, sometime very slowly, reads through the disk it gives a crude graphical representation of which bits of disk it has succesfully read, and which bits have too many errors.

 I was very surprised as to how many errors were on my disk. It could have been faulty blank media, but I strongly suspect my Technika (Tesco own brand) DVD recorder has a failing DVD writer. I may investigate replacing either the burner itself (probably a fairly standard computer part), or replacing the entire unit someday.

 After dvdisaster had finished reading my faulty disk I moved the resulting session.iso file into a directory on it's own. (I used the default output name and directory when I first used dvdisaster, and with hindsight I realise I could have had the ouput file sent anywhere I liked).

 Now it was time for the magic to start, and to do this it was time to drop down to the command line.  I had things fairly easy at this point. I was using the KDE file manager konqueror, and a simple mouse click opens up a terminal with the path to the working directory already set. I then issued the following command :-
split -a6 -b1048576 -d session.iso dvd
 This uses the bash shell split command to split the big session.iso file into 1 MB numbered files, and prefix the file names with dvd.

 Now comes the clever bit. Leaving the terminal open to do some more command line stuff later, it's back to konqueror which (maybe after a refresh) now shows hundreds of small 1 MB files. Most of them konqueror identifies as mpeg files, and although very short, it is possible to play them using kaffeine, or something similar. By clicking on the column called "filetype" in konqueror it's possible to sort the files into different types. I then deleted all the files whose names were prefixed with dvd, and were not identified as mpeg files. These files are just blank, or corrupt, data that dvdisaster has included to pad out the iso file.

 Next I clicked on the file name column in konqueror to reshuffle the files back into numerical order. This step is not strictly neccesary because it actually only affects the way konqueror displays the file names, and does nothing to the real file structure. Now it's back to the terminal and another command to type in :-
cat dvd* > vin.mpg
The cat command reads all the files prefixed by dvd and stores the entire result into the file called vin.mpg. The name vin.mpg was taken directly from the web page I originally referenced, but could have been anything I wanted. I subsequently renamed it to red_dwarf.mpg.

 My red-dwarf.mpg file seemed to play OK so I departed from the procedure detailed on the web site here. It is possible that was a mistake because the next few steps, as described, would appear to correct some defects in the video. What I did next was to open my file using Avidemux. Using that I was able to cut the adverts from the beginning and end of the programme, and save the result as an xvid encoded avi file.

 My final file did play with a few glitches, and many of these contributed to lip-sync problems. By the end of the programme these small delays between sound and picture added up to about half a second. It doesn't sound much, but is very obvious. It is possible that had I followed all the steps detailed on that web page this problem might have been reduced, and maybe even eliminated, but for now I am very happy to have recovered a watchable video file from an otherwise totally unreadable disk.

 Sometime later I may try the additional recommended steps to recover the video, but there is also another method I might try. That involves using bittorrents and is a bit of a legal grey area, but hey, I am only getting another back-up to a recording I have already made !