I noticed the problem with the size calculation in nes_rom_extract.py. It should be app1.seek(romoffset+4) before the size calculation (missing +4). Otherwise you're reading the 'NES' string instead of the number of PRG and CHR banks. Also, I don't think any of the official ROMs will have the title footer, but I could be wrong. If they don't, the + 128 can be removed.
I noticed the problem with the size calculation in nes_rom_extract.py. It should be app1.seek(romoffset+4) before the size calculation (missing +4). Otherwise you're reading the 'NES' string instead of the number of PRG and CHR banks. Also, I don't think any of the official ROMs will have the title footer, but I could be wrong. If they don't, the + 128 can be removed.