par2 requires block number when adding additional redundancy; could figure it out for itself

[gwern]

From the man page:

     The "-f" option is used when you create additional recovery data.

       e.g. If you have already created 10% and want another 5% then you migh
       use the following command:

         par2 create -s307200 -r5 -f300 test.mpg

       This specifies the same block size (which is a requirement for addi‐
       tional recovery files), 5% recovery data, and a first block number of
       300.

Spelling of 'migh' aside, having to calculate the exact block number is a hassle on the user. They need to find the last par2 file, calculate the sum, and then specify it (and it's unclear whether the argument should be the sum, or the sum+1; I still don't know).

If one is adding *additional* redundancy, then there must be existing par2 files; why cannot par2 look for the existing ones and figure out the next block number and appropriate parameters? It's quite mechanical and tedious on the part of the user, especially if they've misguessed the right percentage and need to add additional redundancy to multiple directories of par2 files.