JMR-devandClaude Opus 5
b082cea889
There is no usable prebuilt FFmpeg for Android any more. arthenica/ffmpeg-kit is archived and its binaries were deleted from Maven Central, so every com.arthenica:ffmpeg-kit-* coordinate 404s and all of its release tags have zero assets. Maven Central's search index still lists the old versions, which misleads; the files behind those entries are gone. The successor, ffmpeg-kit-next, is source-only by design. Building it ourselves is the only remaining option, not a preference. ffmpeg-kit-next is Nix-only -- there is no plain android.sh, only nix-android.sh and a flake -- so the toolchain lives in a container rather than on the developer's machine. The recipe doubles as the reproducibility artifact F-Droid expects and as the GPL corresponding-source obligation. Four problems this path hits, none of them documented upstream: - The nixos/nix base image already ships bash, coreutils and git; installing them collides with the existing profile entries and fails the image build. - Upstream scripts use #!/bin/bash but the image provides only /bin/sh, so start-android.sh dies with "cannot execute: required file not found" after the entire toolchain has been built. - Gradle's AAPT2 comes from Maven as a prebuilt binary linked against FHS paths that do not exist under Nix, failing with "Daemon startup failed" after the whole native build succeeds. Nixpkgs' Android SDK ships an already-patched aapt2, so Gradle is pointed at that. - A bare '*.aar' find also collects every AAR Gradle unpacked into its own caches, so the copy is scoped to the ffmpeg-kit outputs. The NDK stays at r27d as the flake pins it. Do not "upgrade" to r28+: android/jni/Android.mk applies -Wl,-z,max-page-size=16384 manually precisely because r27 predates automatic alignment, and the result is verified 16 KB compliant as-is. Verified against the produced artifact: every .so on both ABIs reports LOAD align 0x4000, libraries are separate rather than a static monolith as the GPL relinking obligation requires, and the embedded configure line confirms --enable-gpl --enable-version3 with x264, x265, SVT-AV1, LAME, libass and the MediaCodec wrappers. Note that --enable-small and --enable-lto internalize symbols, so absence from strings output proves nothing; check the configure line instead. The 35 MB AAR itself is gitignored. F-Droid strips checked-in prebuilt native libraries, and the recipe is the artifact of record. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
5.6 KiB
FFmpeg build
Builds ffmpeg-kit-next into an Android
AAR that the app consumes.
Why this exists
arthenica/ffmpeg-kit — the library nearly every Android FFmpeg tutorial still points at
— was archived, and its binaries were deleted from Maven Central. Every
com.arthenica:ffmpeg-kit-* coordinate now returns 404, and all of its GitHub release
tags have zero attached assets. Maven Central's search index still lists the old
versions, which is misleading; the files behind those entries are gone.
Its successor, ffmpeg-kit-next, is source-only by design and publishes no
prebuilt packages. So building FFmpeg ourselves is not a preference, it is the only
remaining option.
Community forks publishing prebuilt 16 KB-aligned AARs do exist, but each fails on license, ABI coverage, or publisher credibility — and at least one redistributes a non-free FDK-AAC build, which FFmpeg states is unredistributable.
Why a container
ffmpeg-kit-next is Nix-only. There is no plain android.sh; the repository ships
nix-android.sh plus a flake, and the flake pins the entire toolchain including
Android NDK 27.3.13750724 (r27d).
Rather than install Nix on a developer machine, the toolchain lives in a container image. That keeps the host clean and doubles as the reproducibility artifact F-Droid wants.
Note the NDK version: do not "helpfully" upgrade to r28+. The flake pins r27d and
android/jni/Android.mk applies -Wl,-z,max-page-size=16384 manually for arm64-v8a
and x86_64 precisely because r27 predates automatic 16 KB alignment. The output is
16 KB compliant as-is.
Usage
podman build -t ffmpeg-kit-builder:local -f Containerfile .
mkdir -p out
podman run --name ffmpeg-build -v "$PWD/out":/work/out:Z \
localhost/ffmpeg-kit-builder:local full
Two modes:
| Mode | Libraries | Purpose |
|---|---|---|
spike |
minimal | Validates the toolchain end to end without waiting on x264/x265/SVT-AV1 |
full |
shipping set | The GPL configuration that ships |
The run deliberately omits --rm: the container's writable layer retains the several
gigabytes of Nix store contents (Android SDK and NDK), so subsequent builds skip the
download. Reuse it with podman start -a ffmpeg-build.
Only arm64-v8a and x86_64 are built, matching the app's abiFilters. Dropping the
32-bit ABIs roughly halves both build time and APK size, and Play does not require them.
Library selection
Flag names come from get_library_name() in the upstream scripts/function.sh. Two
that are easy to get wrong:
- It is
--enable-lame, not--enable-libmp3lame. - It is
--enable-libsvtav1for SVT-AV1.
MP3 deserves a note: Android has no MP3 encoder at any API level. That is a platform
gap, not a Media3 limitation, so --enable-lame is the only way the app can output MP3.
--enable-android-media-codec gives FFmpeg the h264_mediacodec / hevc_mediacodec
wrappers (added in FFmpeg 6.0). These act as a fallback-within-the-fallback: hardware
encode from the FFmpeg side when a job was routed away from Media3 for container reasons
but still wants hardware speed.
Licensing
The full build passes --enable-gpl with x264 and x265, which makes the
distributed binary GPL-3.0. This is deliberate — see ../../LICENSES/README.md.
Worth recording, because it is widely misunderstood: libass is ISC licensed, not GPL, so subtitle burn-in does not require the GPL flag. The only things GPL genuinely buys are x264/x265 software encode (and with them CRF and 2-pass rate control), vidstab, and the GPL filter set.
Never build with --enable-nonfree. FFmpeg states it renders the binary
unredistributable.
Verified build output (2026-08-19, ffmpeg-kit-next v8.1.1 / FFmpeg 8.1.2)
The full build produced a 35 MB AAR with 10 shared libraries per ABI for arm64-v8a
and x86_64. Confirmed against the artifact rather than assumed:
- 16 KB page alignment: every
.soon both ABIs reportsLOAD align 0x4000(readelf -lW). This is the hard Play gate. - Separate shared libraries, not a static monolith — which is what the LGPL/GPL relinking obligation requires.
- Embedded configure line (from
strings libavutil.so):--enable-gpl --enable-version3 --enable-libx264 --enable-libx265 --enable-libsvtav1 --enable-libvpx --enable-libmp3lame --enable-libopus --enable-libdav1d --enable-libass --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-mediacodec --enable-jni --enable-shared --enable-small --enable-lto - Present and verified:
libx264(with an x264 core banner, so genuinely linked),libx265,libsvtav1,libmp3lame,h264_mediacodec,hevc_mediacodec,libopus,libdav1d, the GIF encoder and muxer, libass internals (ass_shaper_new), and thesubtitles,scale,palettegen,paletteuseandconcatfilters.
Note --enable-version3: combined with --enable-gpl this makes the binary GPL-3.0,
which is what LICENSES/README.md states.
A caution on verifying this yourself: the build uses --enable-small and --enable-lto,
so internal symbols like ff_libx264_encoder do not appear in strings output.
Their absence proves nothing. Check the configure line and the registered codec names
instead.
Release checklist
GPL-3.0 requires corresponding source alongside the binary. For each release, attach to the GitHub Release next to the APK:
- the exact
ffmpeg-kit-nexttag and FFmpeg version used, - the full configure line (printed in this script's build log), and
- any patches applied.