Commit 1a2d690da2 for ffmpeg

commit 1a2d690da2f28b1177b56e2498a82de2db0efd8d
Author: Michael Niedermayer <michael@niedermayer.cc>
Date:   Sat Oct 10 05:23:52 2026 +0200

    avcodec/h264_cabac: do not adjust the CABAC mb_type of SI slices

    Undefined shift Replicated through API with UBSAN on i386

    Fixes: left shift of 1621233664 by 2 places cannot be represented in type 'int'
    Fixes: 538751135/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_H264_fuzzer-5842595151151104
    Fixes: 88lh9wyp3VpG

    Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
    Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

diff --git a/libavcodec/h264_cabac.c b/libavcodec/h264_cabac.c
index 703b27aa96..7fc4817634 100644
--- a/libavcodec/h264_cabac.c
+++ b/libavcodec/h264_cabac.c
@@ -2018,8 +2018,6 @@ int ff_h264_decode_mb_cabac(const H264Context *h, H264SliceContext *sl)
         }
     } else {
         mb_type = decode_cabac_intra_mb_type(sl, 3, 1);
-        if (sl->slice_type == AV_PICTURE_TYPE_SI && mb_type)
-            mb_type--;
         av_assert2(sl->slice_type_nos == AV_PICTURE_TYPE_I);
 decode_intra_mb:
         partition_count = 0;