ffmpeg_4: fix crash with clang 16

ffmpeg_4 crashes in `ff_seek_frame_binary` due to UB and optimizations
clang 16 performs. This is fixed upstream in ffmpeg_5, but the patch can
be made to apply to ffmpeg_4.

pkgs/development/libraries/ffmpeg/4.nix

@@ -7,5 +7,17 @@ import ./generic.nix rec {
       url = "https://git.ffmpeg.org/gitweb/ffmpeg.git/patch/031f1561cd286596cdb374da32f8aa816ce3b135";
       hash = "sha256-mSnmAkoNikDpxcN+A/hpB7mUbbtcMvm4tG6gZFuroe8=";
     }
+    # The upstream patch isn’t for ffmpeg 4, but it will apply with a few tweaks.
+    # Fixes a crash when built with clang 16 due to UB in ff_seek_frame_binary.
+    {
+      name = "utils-fix_crash_in_ff_seek_frame_binary.patch";
+      url = "https://git.ffmpeg.org/gitweb/ffmpeg.git/patch/ab792634197e364ca1bb194f9abe36836e42f12d";
+      hash = "sha256-UxZ4VneZpw+Q/UwkEUDNdb2nOx1QnMrZ40UagspNTxI=";
+      postFetch = ''
+        substituteInPlace "$out" \
+          --replace libavformat/seek.c libavformat/utils.c \
+          --replace 'const AVInputFormat *const ' 'const AVInputFormat *'
+      '';
+    }
   ];
 }