After every encode of a track, I get the message
on the command line several times.
My guess is that it has to do with my changing the encoding of ID3v2 tags to ISO_8859_1. The guess is supported by this snippet from id3.c
/* Always encode pretending it is ascii */
I found ISO_8859_1 in the docs somewhere, but a
% grep -i iso .grip*
Be careful: my guessing could be completely misleading.
P.S.: Grip is just right. Whenever I thought it should be able to do this or that, I found the feature already. Great software.