With titles like this in the meta data:
The Four Seasons (Il quattro stagione), concertos (4) for violin, strings & continuo ("Il cimento" Nos. 1-4) , Op. 8/1 - 4: No. 1 In E Major, RV 269 "La primavera"~Movement 3, Allegro
It seems the aac encoder gets stuck (I tried waiting for 5 minutes, all the CoreEncoder processes seemed to be stuck.

I tried changing just the ~, but that made no difference. Removing the double quotes seemed to fix the issue.

I guess some parsing has trouble with escaping/quoting ...