The
codec IDs in Matroska files are written as cleartext and can be read by using a
hex editor or by opening them (either Matroska or MP4) in
MkvToolNix. If you choose to remux the opened file, the status dialog box might show longer description of the "demultiplexer" and "output module" used for each stream.
In case of V_MS/VFW/FOURCC, this (a little obsolete) list of known FourCCs might be helpful. It is basically the same as the list of known video compression formats in GSpot:
http://abcavi.kibi.ru/fourcc.htm
In case of A_MS/ACM, you can also consult GSpot's list of known ACM codes (or use Google).