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>
Media Converter
A free and open-source media converter for Android — batch video transcoding and compression, audio extraction and conversion, GIF and frame export, and file merging.
Android 13+ (API 33). Built with Jetpack Compose and Material 3.
Status: early development. The project scaffold and UI shell exist; the conversion pipeline is being built out. Not yet usable.
Licensing at a glance
- Source code: MIT
- Distributed APK: GPL-3.0 — because it bundles FFmpeg built with x264/x265
That split is deliberate, not an oversight. See LICENSES/README.md
for the reasoning and the corresponding-source obligations.
Architecture
Two conversion engines behind an explicit router, because neither one covers the job alone.
AndroidX Media3 Transformer — the hardware path
Handles the common cases: MP4/MOV in and out, H.264/HEVC, resolution and frame-rate changes, rotation, overlays, audio to AAC, and stream-copy transmuxing. Fully hardware accelerated end to end — MediaCodec decodes to a GL surface and MediaCodec re-encodes, so frames never round-trip through the CPU. Roughly 7–8× realtime on 720p.
FFmpeg — the long tail
Everything Media3 structurally cannot do:
- Containers outside MP4/WebM/Ogg/WAV/AAC — MKV, AVI, FLV, MPEG-TS
- MP3 output — Android has no MP3 encoder at any version; this is a platform gap
- GIF and image sequences
- Input codecs with no platform decoder on the device
- CRF and 2-pass rate control, for the quality tier
Quality tiers
The router is surfaced to users as a quality choice rather than hidden:
| Tier | Engine | Rate control | Trade-off |
|---|---|---|---|
| Fast (default) | Media3 / MediaCodec | bitrate-targeted | ~7–8× realtime, low battery cost |
| Best quality | FFmpeg + x264/x265 | CRF or 2-pass | ~realtime or slower, better quality per byte |
A note on "GPU acceleration"
Android has no GPU video codec path. There are three distinct tiers, and conflating them causes a lot of confusion:
- Fixed-function video codec silicon — reached through
MediaCodec. This is what "hardware accelerated" means for encode and decode. It is not the GPU. - GPU shader cores — genuinely used, but only for filters, scaling, and color effects on already-decoded frames, via OpenGL ES. Never for entropy coding.
- CPU — x264, x265, and software decoders.
FFmpeg's -hwaccel is meaningful on Android only as mediacodec, and even then it
targets direct-to-Surface playback rather than file-to-file transcoding. Vulkan Video
exists in FFmpeg 8.0+ but no shipping Android GPU driver exposes it — no VK_KHR_video_*
extension appears in any Android Vulkan Profile tier.
So this app is hardware accelerated via MediaCodec, and GPU accelerated for effects via GL shaders. Both are real; neither is "the GPU decoding video."
Building
Requires JDK 17+ and the Android SDK with API 37.
./gradlew :app:assembleDebug
The FFmpeg native library is built separately from source; that build is not yet wired into this repository.
Contributing
Contributions are welcome. Note that contributions to the source are under MIT, while
the distributed binary remains GPL-3.0 for the reasons described in LICENSES/README.md.