FFmpeg 7.1 + cuframes input demuxer

Snapshot FFmpeg n7.1 (release tag) с применённым patch'ем для cuframes
input format. Используется как FFMPEG_REPO_OVERRIDE в NickM-27/FFmpeg-Builds
fork для статической сборки patched binary под Frigate (Debian 12 / glibc 2.36).

Apply changes:
  + libavformat/cuframesdec.c (новый — реализация демуксера)
  M libavformat/Makefile (CONFIG_CUFRAMES_DEMUXER target)
  M libavformat/allformats.c (extern declaration)
  M configure (--enable-libcuframes option + dep check)

Patch source: https://git.goldix.org/gx/cuframes (filter/ffmpeg-7.1-cuframes-demuxer.patch)

History сброшена (snapshot вместо fork) потому что upstream shallow clone
не позволял push в gitea. Полная история FFmpeg — на github.com/FFmpeg/FFmpeg n7.1.

libavcodec/startcode.c

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2003-2010 Michael Niedermayer <michaelni@gmx.at>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * Accelerated start code search function for start codes common to
+ * MPEG-1/2/4 video, VC-1, H.264/5
+ * @author Michael Niedermayer <michaelni@gmx.at>
+ */
+
+#include "libavutil/intreadwrite.h"
+#include "startcode.h"
+#include "config.h"
+
+int ff_startcode_find_candidate_c(const uint8_t *buf, int size)
+{
+    int i = 0;
+#if HAVE_FAST_UNALIGNED
+    /* we check i < size instead of i + 3 / 7 because it is
+     * simpler and there must be AV_INPUT_BUFFER_PADDING_SIZE
+     * bytes at the end.
+     */
+#if HAVE_FAST_64BIT
+    while (i < size &&
+            !((~AV_RN64(buf + i) &
+                    (AV_RN64(buf + i) - 0x0101010101010101ULL)) &
+                    0x8080808080808080ULL))
+        i += 8;
+#else
+    while (i < size &&
+            !((~AV_RN32(buf + i) &
+                    (AV_RN32(buf + i) - 0x01010101U)) &
+                    0x80808080U))
+        i += 4;
+#endif
+#endif
+    for (; i < size; i++)
+        if (!buf[i])
+            break;
+    return i;
+}