From 2dd9d8338b6d1b3f0dccc6c45aa4ffc5681e6ede Mon Sep 17 00:00:00 2001
From: Goatman13 <101417270+Goatman13@users.noreply.github.com>
Date: Sun, 29 May 2022 18:48:39 +0200
Subject: [PATCH] IPU: Implement start code validation for BDEC/IDEC

According to MPEG specs when 8 "0" bits are found, we should check for 000001xxh. Recommended way is to check 24 bits (000001h), and if they won't match discard 8 bits and try again until valid code is found, or stream ends.
---
 pcsx2/IPU/mpeg2lib/Mpeg.cpp | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/pcsx2/IPU/mpeg2lib/Mpeg.cpp b/pcsx2/IPU/mpeg2lib/Mpeg.cpp
index c8b27176b2..2014b793ac 100644
--- a/pcsx2/IPU/mpeg2lib/Mpeg.cpp
+++ b/pcsx2/IPU/mpeg2lib/Mpeg.cpp
@@ -920,6 +920,7 @@ finish_idec:
 	case 3:
 	{
 		u8 bit8;
+		u32 start_check;
 		if (!getBits8((u8*)&bit8, 0))
 		{
 			ipu_cmd.pos[0] = 3;
@@ -929,7 +930,21 @@ finish_idec:
 		if (bit8 == 0)
 		{
 			g_BP.Align();
-			ipuRegs.ctrl.SCD = 1;
+			do
+			{
+				if (!g_BP.FillBuffer(24)) 
+				{
+					ipu_cmd.pos[0] = 3;
+					return false;
+				}
+				start_check = UBITS(24);
+				if (start_check == 1)
+				{
+					ipuRegs.ctrl.SCD = 1;
+					break;
+				}
+				DUMPBITS(8);
+			} while (start_check != 1);
 		}
 	}
 		[[fallthrough]];
@@ -1196,6 +1211,7 @@ __fi bool mpeg2_slice()
 	case 4:
 	{
 		u8 bit8;
+		u32 start_check;
 		if (!getBits8((u8*)&bit8, 0))
 		{
 			ipu_cmd.pos[0] = 4;
@@ -1205,7 +1221,21 @@ __fi bool mpeg2_slice()
 		if (bit8 == 0)
 		{
 			g_BP.Align();
-			ipuRegs.ctrl.SCD = 1;
+			do
+			{
+				if (!g_BP.FillBuffer(24)) 
+				{
+					ipu_cmd.pos[0] = 4;
+					return false;
+				}
+				start_check = UBITS(24);
+				if (start_check == 1)
+				{
+					ipuRegs.ctrl.SCD = 1;
+					break;
+				}
+				DUMPBITS(8);
+			} while (start_check != 1);
 		}
 	}
 		[[fallthrough]];