git pack-objects input list

Hi,

While playing around with git-pack-objects, it seemed to me that the
input it can take is not a simple list of object SHA1s. Unfortunately,
the man page is not very verbose about that. While I'd happily send a
patch for that, I'd prefer to actually know what kind of input it can
take, and what it uses it for.

AFAICT, it can take the output of git-rev-list --all --objects (so,
SHA1s followed by file names for blobs), which seems to be the same as
what git-pack-objects --revs does internally, but it seems to have a
string impact on how deltas are calculated (not giving file names makes
it create a smaller pack in some cases, a bigger one in other cases).

Could someone knowing the delta calculation internals enlighten me ?

Thanks

Mike