Here's a sample SHP, pure black (with unittem, no bg), 2 frames:

00 00 08 00 08 00 02 00

00 00 00 00 08 00 08 00 00 00 00 00 00 00 07 00 00 00 00 00 38 00 00 00
00 00 00 00 08 00 08 00 00 00 00 00 00 00 00 00 00 00 00 00 78 00 00 00

0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C

0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C
0C 0C 0C 0C 0C 0C 0C 0C

Hope that displays properly.

I've gotten everything down except for part of the 2nd & 3rd lines. Eg, the 2nd line:

00 00 00 00 08 00 08 00 00 00 00 00 00 00 07 00 00 00 00 00 38 00 00 00

The first 20 bytes I understand (not fully, but enough).
Concerning the last 4: bytes 21 & 22 seem to be critical. Messing with them will mess up the SHP, and they're always non-zero (except for a blank SHP). They seem to follow some vague patterns, and depend on the total number of frames and other factors.

What are they? How are they calculated?

The last two bytes are sometimes non-zero but they seem to be arbitrary. Correct?

BTW, I typed this twice. The first time the page refreshed automatically. The second time I typed faster.

meselfs himself!