VidMaker static FFmpeg/ffprobe source and reconstruction materials

This companion covers only the exact helper hashes in MANIFEST.json. It
does not attest historical VidMaker binaries or contain proprietary app
objects. FFmpeg/ffprobe are separate executables invoked by VidMaker.

sources/upstream contains pinned FFmpeg 7.1.5 and OpenH264 2.6.0 source.
sources/distro contains each retained runtime/header package's exact Debian
source control file, upstream archive and distro patches; SOURCE-RECORD.json
records checksums. sdk contains relocatable static runtime archives, startup
objects and headers extracted from the recorded exact binary packages, not
compiler executables. INPUTS.json records all identities and compiler paths.

Prepare a Linux amd64 SDK with GCC/G++ 13, GNU binutils, make, nasm,
pkg-config, Python 3, curl, tar and xz. Windows builds additionally require
the recorded x86_64-w64-mingw32 GCC/G++ 13-win32 toolchain. These standard
compiler/OS build tools are prerequisites; no network is used to acquire
source or runtime material during reconstruction. build/static-source-builder.Dockerfile
in the VidMaker repository documents a compatible tool environment. Wine64
is used to execute Windows codec tests, not bundled with the helpers.

From the extracted companion, with a fresh output directory:

  JOBS=4 python3 scripts/static_source.py build \
    --material "$PWD" --work "$PWD/work" --output "$PWD/output"

The compiler wrappers use the supplied sdk for headers, static libraries
and startup objects. Link maps prove which objects were used. No VidMaker
source, object files, private keys or network access are required.

To modify FFmpeg, edit the extracted work/ffmpeg-7.1.5 source, then run
make -C work/build ffmpeg ffprobe (Windows: ffmpeg.exe ffprobe.exe). The
included source and runtime objects permit relinking the separate helpers.
To modify a runtime, extract its .dsc with dpkg-source -x, retain/apply the
included distro patches and rebuild using its supplied debian/rules and
matching build prerequisites; replace the affected sdk objects and relink.
GCC packaging contains the GCC upstream tarball plus distro patches; the
gcc-mingw-w64 packaging uses the exact underlying GCC source version recorded
in INPUTS.json, not the native compiler's newer source package.

FFmpeg libraries remain LGPL-2.1-or-later. Linux glibc remains LGPL under
its supplied terms; its corresponding source and startup objects are
included. zlib, OpenH264 and MinGW CRT/import stubs retain their supplied
per-file licenses. Windows system DLLs are not distributed here.
Linux glibc network/NSS features may load matching OS NSS modules even in a
static executable; the validated local PNG/H.264/AAC paths do not need them.
GCC runtime
objects/templates retain GCC Runtime Library Exception 3.1 where applicable;
the helpers use the stock GCC eligible compilation process, without a
proprietary compiler plugin. That exception does not waive FFmpeg/glibc
source obligations. Full matching GCC source/patches are retained anyway.
See licenses/*.copyright and all COPYING/LICENSE files in the source packages.

Any VidMaker restriction does not prohibit modification of these helpers
for the recipient's own use or reverse engineering to debug modifications
(LGPL-2.1 section 6). Source/relink material is provided under sections 4
and 6(a)/(d). Copy rebuilt helpers beside the packaged executable in a user-
controlled copy of the distribution. Preserve the original package and its
notices. Signing the original proprietary app is not required to rebuild the
helpers. These materials do not grant codec patent rights; retained codec
notices continue to apply.
