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in repository ffmpeg.

commit 8eecba02c79fc99a3f127704f8b5843a20e6012d
Author:     Michael Niedermayer <[email protected]>
AuthorDate: Wed Jan 21 02:31:51 2026 +0100
Commit:     Michael Niedermayer <[email protected]>
CommitDate: Tue Mar 3 00:47:21 2026 +0100

    avcodec/mpegvideo_enc: Restructure ff_h263_encode_gob_header() relation to 
update_mb_info()
    
    Fixes: out of array access
    
    Found-by: Zhenpeng (Leo) Lin from depthfirst
    Signed-off-by: Michael Niedermayer <[email protected]>
---
 libavcodec/mpegvideo_enc.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/libavcodec/mpegvideo_enc.c b/libavcodec/mpegvideo_enc.c
index aad78eed4a..90ff7bf1cb 100644
--- a/libavcodec/mpegvideo_enc.c
+++ b/libavcodec/mpegvideo_enc.c
@@ -2918,7 +2918,7 @@ static void write_mb_info(MPVEncContext *const s)
     bytestream_put_byte(&ptr, 0); /* vmv2 */
 }
 
-static void update_mb_info(MPVEncContext *const s, int startcode)
+static void update_mb_info(MPVEncContext *const s)
 {
     if (!s->mb_info)
         return;
@@ -2926,14 +2926,6 @@ static void update_mb_info(MPVEncContext *const s, int 
startcode)
         s->mb_info_size += 12;
         s->prev_mb_info = s->last_mb_info;
     }
-    if (startcode) {
-        s->prev_mb_info = put_bytes_count(&s->pb, 0);
-        /* This might have incremented mb_info_size above, and we return 
without
-         * actually writing any info into that slot yet. But in that case,
-         * this will be called again at the start of the after writing the
-         * start code, actually writing the mb info. */
-        return;
-    }
 
     s->last_mb_info = put_bytes_count(&s->pb, 0);
     if (!s->mb_info_size)
@@ -3147,8 +3139,11 @@ static int encode_thread(AVCodecContext *c, void *arg){
 #endif
                     case AV_CODEC_ID_H263:
                         if (CONFIG_H263_ENCODER) {
-                            update_mb_info(s, 1);
+                            if (s->mb_info && put_bytes_count(&s->pb, 0) - 
s->prev_mb_info >= s->mb_info)
+                                s->mb_info_size += 12;
+
                             ff_h263_encode_gob_header(s, mb_y);
+                            s->prev_mb_info = put_bits_count(&s->pb)/8;
                         }
                     break;
                     }
@@ -3173,7 +3168,7 @@ static int encode_thread(AVCodecContext *c, void *arg){
             s->c.mb_skipped = 0;
             s->dquant=0; //only for QP_RD
 
-            update_mb_info(s, 0);
+            update_mb_info(s);
 
             if (mb_type & (mb_type-1) || (s->mpv_flags & FF_MPV_FLAG_QP_RD)) { 
// more than 1 MB type possible or FF_MPV_FLAG_QP_RD
                 int next_block=0;

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