FFmpeg shared-library source and rebuild instructions

This release uses FFmpeg 7.1.4 (LGPL version 2.1 or later), without GPL or
nonfree components. The upstream source archive is included here unchanged:
ffmpeg-7.1.4.tar.xz
SHA-256: 71f4aac3573ed9060489cb62526a6c7dda815ae10993789611acd7be9fa9fbf4
Upstream: https://ffmpeg.org/releases/ffmpeg-7.1.4.tar.xz

The exact Python recipe used for the included DLLs is build_ffmpeg_windows.py.
It extracts into a separate output directory, configures the minimal H.264,
ATRAC3/ATRAC3+ and swscale libraries, builds them and records hashes in build.json.
configuration.json records the actual configuration and binary hashes.

Install Python 3.12+ and obtain the official w64devkit x64 2.11.0 toolchain
(GCC 16.2.0). From this folder run, substituting your w64devkit bin directory:

  python build_ffmpeg_windows.py --archive ffmpeg-7.1.4.tar.xz --toolchain "C:\w64devkit\bin" --output rebuilt

The compatible replacement DLLs appear under rebuilt/install/bin/. Close the
game and replace avcodec-61.dll, avutil-59.dll and swscale-8.dll beside
Asphalt2.exe. Keep those ABI major versions and build for Windows x64.
The player imports the public FFmpeg API dynamically; no relink of the player
is required. Modifying/replacing FFmpeg for your own use and debugging such
modifications is permitted. No FFmpeg source modifications were made.

Full licenses are in ../licenses and inside the source archive. This package
includes the corresponding FFmpeg source directly, so no later source offer or
network access is needed to obtain it. Compiler binaries are not bundled.
