Commit f91b54fbe3 for ffmpeg

commit f91b54fbe3fdbb4e9c5bb82735c329012d1fa27c
Author: Michael Niedermayer <michael@niedermayer.cc>
Date:   Fri Oct 16 22:21:59 2026 +0200

    avcodec/libaribcaption: make the default alpha values unsigned

    ARIBCC_MAKE_RGBA() shifts the alpha value left by 24 bits, which does
    not fit in an int for the defaults 0xFF and 0x80.

    Fixes: libavcodec/libaribcaption.c:650:37: runtime error: left shift of 255 by 24 places cannot be represented in type 'int'
    Fixes: undefined shift
    Undefined shift Replicated through UnModified FFmpeg with UBSAN

    Found during triage/review of the security report AISLE-2026-R0043 (AISLE-2026-0150-00333, 6vQDuOhjPDP6)

diff --git a/libavcodec/libaribcaption.c b/libavcodec/libaribcaption.c
index e8f7cada73..340e8866f8 100644
--- a/libavcodec/libaribcaption.c
+++ b/libavcodec/libaribcaption.c
@@ -39,8 +39,8 @@
 #define ARIBC_BPRINT_SIZE_INIT         64
 #define ARIBC_BPRINT_SIZE_MAX          (8 * 1024)
 #define ARIBC_ALPHA_MAX_NUM            4
-#define ARIBC_ALPHA_DEFAULT_FRONT      0xFF
-#define ARIBC_ALPHA_DEFAULT_BACK       0x80
+#define ARIBC_ALPHA_DEFAULT_FRONT      0xFFu
+#define ARIBC_ALPHA_DEFAULT_BACK       0x80u

 #define ARIBCC_COLOR_RGB(c)            ((c) & 0xFFFFFF)
 #define ARIBCC_COLOR_DIFF_RGB(c1,c2)   (((c1) ^ (c2)) & 0x00FFFFFF)