From 27b080238526aa77099314808daeb838a350335a Mon Sep 17 00:00:00 2001
From: Chris Tallon <chris@vomp.tv>
Date: Thu, 12 Jun 2025 15:55:00 +0000
Subject: [PATCH] Fix ITV2 frame counting bug

---
 src/demuxer.cc | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/demuxer.cc b/src/demuxer.cc
index 2e7e793..1430131 100644
--- a/src/demuxer.cc
+++ b/src/demuxer.cc
@@ -451,7 +451,26 @@ u4 PESPacket::countPictureHeaders(bool h264, struct PictCountInfo& pinfo) const
 	  {
           pos++;
 		  pattern = (pattern << 8) | data[pos];
-          if (pattern==DEMUXER_PIC_HEAD) count++;
+          if (pattern==DEMUXER_PIC_HEAD)
+          {
+            count++;
+          }
+          // Now also search for EXT_START_CODE headers and if it's a Picture Coding Extension,
+          // and the picture structure is set to interlaced - bottom field (2), reverse the frame count by 1
+          else if (pattern == 0x000001b5) // EXT_START_CODE
+          {
+            u1 extbyte1 = data[pos+1];
+
+            if ((extbyte1 & 0xF0) == 0x80) // First 4 bits are 0001
+            {
+              u1 extbyte3 = data[pos+3];
+              u1 picstruct =  extbyte3 & 0x3;
+              if (picstruct == 2)
+              {
+                count--;
+              }
+            }
+          }
 	  }
 	  return count;
   }
-- 
2.39.5