JMR-devandClaude Opus 5
fa10d94192
publish deletes a destination it could not write to -- D4's fix, so a failed save does not leave a truncated file at the name the user chose -- but only when that destination was positively zero bytes first. destinationIsKnownEmpty is careful that "I could not tell" never authorises a delete, which makes the precondition load-bearing. Until now that precondition was asserted only against a fake built to match it: OutputPublisherPublishTest writes ByteArray(0) into FakeSafProvider before each case, under a comment stating this is how CreateDocument behaves. If it were false in production, D4's fix would be inert and every existing test would still pass. It is not false. Measured on an API 34 emulator against the real dialog: the document SAF hands back is a document URI and reports a size of exactly zero before anything writes to it. RecordingPublisher reads both at the moment publish sees them, through the ConversionDependencies seam, then lets the real copy proceed so the bytes are checked too. This has to go through the picker, and through the app, and both are platform constraints rather than choices. E7 in docs/e2e-read-findings.md records the first: a DocumentsProvider is reachable only through a picker-issued grant. The second was measured here -- a host Activity in this source set owning its own CreateDocument launcher cannot be started at all, because instrumentation runs in the target app's process and ActivityScenario refuses with "Intent in process org.libremediaconverter resolved to different process org.libremediaconverter.test". So #226 has no cheap half, which is what its comment now says. Three things the flow needed, each measured rather than guessed: Both taps scroll first. On Ready the screen carries a file card, five pickers and then the button, so Convert is below the fold; performClick on an off-screen node dispatches where nothing is and throws nothing, while assertIsEnabled passes either way. The first version sat waiting for a Converted that could never come. The format stays at its default. FixtureDocumentsProvider advertises video/mp4 so the picker's MIME filter has a mutation with a shape, and DocumentsUI honours that on the save side too: choosing MP3 makes the destination audio/mpeg and the fixture root is filtered out of the save dialog entirely. The notification dialog is dismissed rather than pre-granted. Convert converts from the permission callback whichever way the answer goes, so denying is a real user's path and enough. Granting programmatically did not take -- GrantPermissionsActivity appeared anyway and swallowed the tap. The provider gains create, write and delete support, which it needs to be a save target at all. It carries @FailsOnEmulatorApi37 because anything that puts DocumentsUI on screen aborts system_server on that image, as #245 established for the other two; baseline 5 -> 6. Verified on a local API 34 emulator: three full-suite runs at 70/0/0/3, and a publish that writes no bytes fails it with "array lengths differed, expected.length=58677 actual.length=0". Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
LibreMediaConverter
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: working, unreleased. Both conversion engines, the router, the background job queue and the join flow are implemented and building. The FFmpeg format tests run green on a physical Pixel 10 Pro XL (API 37) and on local emulators at API 33–36, and CI runs the instrumented suite at API 33–36 on every pull request.
Correction (R18 / #27, 2026-08-22): this line used to say the FFmpeg format tests had "been
written but not yet executed on a device" — true when written, false from the first device pass,
and never updated. FFmpegEngineTest's nine format tests were in every run named above and none
of them failed; the runs are recorded under "Verified on real API 37 hardware" in
docs/api-37-emulator-crash.md and "The sweep, run" in
docs/local-emulator.md. API 37 has no CI row — that emulator image is
broken — so it stays a manual Pixel check before each release.
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: H.264/HEVC, resolution and frame-rate changes, rotation, overlays, and audio to AAC. 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.
It writes MP4 and nothing else. media3-muxer ships WebM, Ogg, WAV and AAC muxers too,
but none can be driven by Transformer — they throw from addMetadataEntry, which the muxer
wrapper calls for every metadata entry a real recording carries. It reads far more than it
writes, Matroska included, which is what makes MKV → MP4 a hardware remux.
FFmpeg — the long tail
Everything Media3 structurally cannot do:
- Containers outside MP4/WebM/Ogg/WAV/AAC — MKV, MOV, AVI, FLV, MPEG-TS, WMV/ASF
- 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
- Codecs Media3's muxers decline even on a stream copy — its MP4 muxer carries AAC, Opus, Vorbis and PCM, but neither MP3 nor FLAC
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."
Remuxing
Changing the container without touching the streams. Copying an H.264 track from MKV into MP4 moves the same samples into a different wrapper: it finishes in seconds instead of minutes, costs no quality, and needs no encoder — which is why it stays on the hardware path even on a device that cannot encode the codec in question.
Copy is a codec choice like any other, so it can be mixed: copy the video and re-encode
only the audio, or the reverse. Picking a codec the source already uses is upgraded to a
copy automatically when the container is changing — if container and codec both already
match, the only reason to run the job is to re-encode it, so it does.
A copy is never attempted on a stream whose codec could not be identified. A needless re-encode costs time; a wrong stream copy costs a file that will not play.
Features
| Formats | |
|---|---|
| Video out | MP4, MOV, MKV, WebM, MPEG-TS, AVI, FLV, WMV/ASF |
| Video codecs | H.264, H.265, VP9, or copy the source stream |
| Audio out | MP3, AAC/M4A, FLAC, Opus, WAV, MKA |
| Audio codecs | AAC, Opus, MP3, FLAC, PCM, or copy the source stream |
| Images | GIF, PNG frame sequences |
| Other | Remux without re-encoding; join several files into one |
Presets cover the common combinations in one tap. The Advanced picker exposes the full container × codec matrix — including combinations that cannot work, which it explains and offers alternatives for rather than hiding.
Conversions run as durable background work, so they survive leaving the app and are restored when you reopen it.
One case is not restored, and it is worth knowing about. If Android refuses to let a job restart in the background, it is retried on an exponential backoff for about eight and a half hours and then given up on — and a job that has been given up on does not come back when you reopen the app. Reopening the app is what grants permission to run, so a conversion that has stalled this way is best started again from the app rather than waited on.
Building
Requires the Android SDK with API 37. Do not pick a JDK — the repo does.
gradle/gradle-daemon-jvm.properties pins the daemon to Java 25 and carries foojay
download URLs per platform, so Gradle finds an installed Java 25 or downloads one on the
first build, whatever JAVA_HOME points at. JAVA_HOME only chooses the launcher, which
Gradle 9.7.1 will run on Java 8 or newer. Everything the build actually compiles is Java 25,
the app's own bytecode included. ./gradlew --version prints the launcher and the daemon
separately, and they routinely differ.
FFmpeg is committed as a prebuilt archive under bin/, so a clone
builds without a cross-compile. That is deliberate: rebuilding it per CI run made test
results ambiguous, because a red build could mean broken code or a build that hiccuped.
See bin/README.md for its provenance and how to regenerate it.
./gradlew :app:assembleDebug # debug APK
./gradlew :app:testDebugUnitTest # JVM tests
./gradlew :app:connectedDebugAndroidTest # device tests, needs a running device
./gradlew :app:assembleRelease # R8-minified release
See tools/ffmpeg/README.md for why the build is
containerised and which flags matter. That recipe remains the authority — the committed
archive is its output, and is also what satisfies the GPL corresponding-source
obligation.
Testing
Unit tests cover the parts that decide correctness without needing hardware: the routing matrix, the container × codec capability matrix, the FFmpeg argument builder, and both stream-copy-versus-re-encode planners. They run against fabricated device profiles, so branches like "this device cannot encode HEVC" are reachable regardless of what the test machine is.
Instrumented tests cover the parts that only a device can prove: real hardware
transcoding, the foreground service type, and each FFmpeg output format asserted against
the produced file rather than the exit code. The remux tests additionally assert which
engine ran — a stream copy produces an identical file either way, so an output-only
assertion cannot tell a hardware transmux from FFmpeg's -c copy.
Privacy
The app has no INTERNET permission, so it cannot open a network connection at all.
Nothing is uploaded, and there is no analytics or advertising. See PRIVACY.md,
which also explains the permissions WorkManager adds automatically.
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.