If you've already successfully extracted them (that usually tends to be the biggest problem for me), try running 'em through Format Factory. It has a pretty high success rate with converting ancient formats.
CPK files shouldn't be reencoded, Windows can decode them natively, the only problem is that they are in a non-avi container.
ACPK2AVI works fine on my end (just tested it, also win7 64bit). It is command line only, but for CPK files you can just copy the cpk files into the same directory as the exe, and type in "acpk2avi.exe input.cpk output.avi" (minus quotes) at the explorer Title Bar.
I got it working, but it took some effort. For some reason I can only get it working by inputting the full dir locations e.g. "c:\acpk2avi.exe c:\test.cpk k:\test.avi". I've noticed the audio of the avi files has a clicking sound? video is fine.
I've also been messing about with FFMPEG which (supposedly) can also demux/remux sega film & cpk files. Again, this is a command line program so I'm having some difficulty getting it to run right on my system.
Now after many hours of faffing about I've been able to make 1 new CPK file, but now I need help putting the new file back into the game to test it.