RPCS3 could not read the encrypted sectors of MGS4. Dumping the game was difficult, and even with a valid IRD, the emulator lacked the CPU/SPU accuracy to process the game's instructions.
In RPCS3 Config:
The introduction of IRD patched ISOs was a watershed moment for MGS4 emulation. It solved the notorious Chapter 4/Act 4 crashes that halted progress for years. mgs4 ird file patched
However, it came with a caveat: File Size. MGS4 is a massive game. To apply an IRD patch, users often had to decrypt the entire game to the hard drive (taking up ~50GB+), rebuild it, and then play it. This required significant storage space and processing time. Furthermore, while IRD patching fixed loading crashes, it initially introduced severe stuttering. Because the emulator had to decrypt massive amounts of data on the fly using the IRD keys, the CPU load was immense. RPCS3 could not read the encrypted sectors of MGS4
Eventually, the community moved toward "Decrypted Folder" dumps (running the game from a folder rather than an ISO), which offered similar stability benefits without the overhead of reading a monolithic ISO file. It solved the notorious Chapter 4/Act 4 crashes