I followed this a little deeper by building mkvextract from source and adding some debug statements. $ echo "113,0,Default,,0,0,0,,♪ ♪" > test.txt $ hexdump -n 180 test.txt # Verify this matches "31 31 33 2C 30 2C 44 65 66 61 75 6C 74 2C 2C 30 2C 30 2C 30 2C 2C C3 A2 E2 84 A2 C2 A...