chore(ffmpeg): vendor macos-arm64 prebuilt tree (captured from CI artifact)

Companion to the already-committed libs/ffmpeg/macos-x86_64/. Captured
from CI run 26064600141 build-macos job (commit b58c97c — the one-shot
upload-artifact step). Together with macos-x86_64 this enables:

1. macOS universal builds: cmake/ffmpeg.cmake can lipo per-arch dylibs
   into a universal tree at build-time when CMAKE_OSX_ARCHITECTURES is
   a list, unblocking CI to ship a universal .app/.vst3/.au/.clap that
   runs on both Apple Silicon and Intel Macs. (Local Intel-only dev
   path unchanged — continues using libs/ffmpeg/macos-x86_64/ directly.)

2. Removing the "Vendor LGPL ffmpeg" step from mac CI: with both trees
   committed, the from-source ffmpeg rebuild on every CI invocation
   becomes redundant. 15-25 min per CI run → ~10 sec git checkout.
   Pattern extends to libs/ffmpeg/windows-x86_64/ + linux-x86_64/ as
   those CI lanes start producing valid trees.

3. Reproducibility: bit-exact same ffmpeg across CI runs and local
   builds (within an arch). The build script (scripts/build_ffmpeg_lgpl.sh)
   stays useful for bumping ffmpeg version + initial vendoring of new
   platforms — just no longer runs every CI invocation.

Tree contents (149 files, 5.5 MB):
- include/{libavcodec,libavformat,libavutil,libswscale,wels}/ — headers
  identical between arches (verified)
- lib/ — ffmpeg 7.1.2 + openh264 2.1.1 arm64 dylibs with the same
  versioned-canonical + symlink-alias layout as macos-x86_64

Symlinks recreated locally — actions/upload-artifact dereferences
symlinks during artifact transport, so the downloaded tree had three
1.5 MB copies of libavcodec.dylib instead of one canonical file + two
symlinks. Re-symlinked to match the macos-x86_64 tree layout (13 MB →
5.5 MB).

License compliance: libs/ffmpeg/LICENSE.LGPL.txt + LICENSE.openh264.txt
at the libs/ffmpeg/ root cover both per-arch trees uniformly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mkschulze

libs/ffmpeg/macos-arm64/include/libavcodec/ac3_parser.h

@@ -0,0 +1,36 @@
+/*
+ * AC-3 parser prototypes
+ * Copyright (c) 2003 Fabrice Bellard
+ * Copyright (c) 2003 Michael Niedermayer
+ *
+ * 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
+ */
+
+#ifndef AVCODEC_AC3_PARSER_H
+#define AVCODEC_AC3_PARSER_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+/**
+ * Extract the bitstream ID and the frame size from AC-3 data.
+ */
+int av_ac3_parse_header(const uint8_t *buf, size_t size,
+                        uint8_t *bitstream_id, uint16_t *frame_size);
+
+
+#endif /* AVCODEC_AC3_PARSER_H */

libs/ffmpeg/macos-arm64/include/libavcodec/adts_parser.h

@@ -0,0 +1,37 @@
+/*
+ * 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
+ */
+
+#ifndef AVCODEC_ADTS_PARSER_H
+#define AVCODEC_ADTS_PARSER_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#define AV_AAC_ADTS_HEADER_SIZE 7
+
+/**
+ * Extract the number of samples and frames from AAC data.
+ * @param[in]  buf     pointer to AAC data buffer
+ * @param[out] samples Pointer to where number of samples is written
+ * @param[out] frames  Pointer to where number of frames is written
+ * @return Returns 0 on success, error code on failure.
+ */
+int av_adts_header_parse(const uint8_t *buf, uint32_t *samples,
+                         uint8_t *frames);
+
+#endif /* AVCODEC_ADTS_PARSER_H */