Here is a method to compress multi track dreamcast games, to shrink the size.
So you have a game with a Track03 then some Audio and a final Data Track. Often Track03 is pretty big. Well here is a way to shrink your multi track games.
First optimize your gdi dump, this converts 2352 to 2048, and reduces size a bit.
So here is the trick, Trac03.iso if you look at it is 99% blank basically a dummy file.
I found out some of the track03.iso files do have some data past the first few hundred sectors, often their is a bit of data at the end of track03 as well, so here is the trick (I use Total Commander to do it).
What you do is this.
I create an empty folder and call it track03 split. Then split track03, using Total Commander into pieces with a file size of 1048576, then I search the folder for duplicate files with the same size and same contents, it will find all the files the exactly the same and send it to your list box, you then delete all those files, then go to your track03 split folder and see what's left, usually it leaves the first file and a couple at the end, be sure to delete the crc file it creates, then just rename the extensions so they are continuous 001, 002, 003 etc... etc. and then join the files into a track03 again then add the iso extension.
What you have then is a smaller track03.iso, something like 2-3 megabytes.
I did find one game that their was a load of data in track03, so I left this game as it was, I think it was Conflict Zone (Europe), but apart from that game, nearly all the others I have done work great, and they all work fine.
Then just run the multi track gdi game with your stripped Track03.iso.
Its not actually compression but its the next best thing.
Here is a link to some Track03.iso files I have already shrunk, if anyone wants to use them make sure the other Tracks you use are from the same game.
The rar contains 39 Track03.iso files all reduced in size...
https://mega.nz/#!Fs4hQJAI!Nfs8DOvOyDDJh...PuDOJeRR5s