VidMaker macOS FFmpeg/ffprobe source and replacement

These are separate executable helpers, not libraries linked into VidMaker.
Their FFmpeg 7.1.5 libraries are statically linked. The complete unmodified
FFmpeg source, including fftools, configure and upstream licenses, is in
sources/ffmpeg-7.1.5.tar.xz. MANIFEST.json records the exact configurations,
source hash and signature-independent helper payload hashes. Apple system
frameworks, libSystem and system libz are dynamic OS dependencies, not bundled
third-party static libraries. This companion covers macOS only.

Offline rebuild (Apple Silicon Mac, Xcode command-line tools, bash, make,
tar, shasum, lipo, otool and an SDK supporting macOS 13):

  FFMPEG_OFFLINE=1 FFMPEG_REBUILD=1 \
  FFMPEG_SOURCE_ARCHIVE="$PWD/sources/ffmpeg-7.1.5.tar.xz" \
  FFMPEG_BUILD_DIR="$PWD/work" FFMPEG_OUTPUT_DIR="$PWD/output" JOBS=4 \
    bash scripts/build-ffmpeg-macos.sh

FFMPEG_ARCHS=arm64 or FFMPEG_ARCHS=x86_64 selects one architecture. An Intel
Mac can build x86_64; the universal build needs an Apple Silicon host capable
of running the x86_64 configure checks. No download is needed. Output is
ffmpeg, ffprobe and the retained license/attribution files. Compiler/SDK
differences may change binary hashes; byte-identical signatures are not a
condition of rebuilding or using modified helpers.

To modify FFmpeg, extract the supplied source, make your changes, repackage
it, and update FFMPEG_SHA256 in your local copy of the included build script
to the new source archive hash. Set FFMPEG_SOURCE_ARCHIVE to that archive.
The recipe records no proprietary application objects because none are
needed to rebuild/relink the helpers from their complete source.

To use rebuilt helpers, work on a copy of VidMaker.app. Replace
Contents/Resources/bin/ffmpeg and ffprobe, preserving executable permissions.
On macOS, changes invalidate the original bundle signature: locally ad-hoc
sign each replacement with codesign --force --sign -, then ad-hoc sign the
copied app. The distributor's signing key or notarization is not required
to make a local modified copy. Keep the original signed application intact.

The FFmpeg helpers and their libraries remain under their upstream terms.
Any VidMaker restriction on modification or reverse engineering does not
restrict modification of these helpers for the recipient's own use or
reverse engineering for debugging such modifications (LGPL-2.1 section 6).
See COPYING.LGPLv2.1 and the license files retained inside the source archive.
The LGPL source/relink materials are provided under sections 4 and 6(a)/(d).
