JMR-devandClaude Opus 5
7f951baf8f
The FFprobe codec vocabulary is written out in at least four places and none of them had a test. Two had already drifted apart. `x264`, `hev1`, `x265` and `vp09` resolved in `CodecNames.videoFromName` and returned null from `AndroidDeviceCodecs.mimeForCodecName`, so the app identified the codec for the source card and for routing and then ran the device capability check blind on the same string; `mpeg4` ran the other way and rendered as a raw name. Nothing could notice, and the reason is structural: a `when` cannot be enumerated, so no test can ask one table what the other one knows. Both are maps now, for that reason alone, and `CodecVocabularyTest` walks the two key sets. A name added to -- or removed from -- one side alone fails the build. The one legitimate asymmetry is listed rather than implied: `mpeg4` is decodable input with no `VideoCodec` to name it, so `CodecNames` is right not to carry it. That list is itself checked, because otherwise it is an escape hatch -- any future divergence could be waved through by adding the name to it, and adding `x265` to it now fails. THIS CHANGES BEHAVIOUR for `x264`, `hev1`, `x265` and `vp09`. A null from `mimeForCodecName` means "unknown to us: assume the platform can handle it and let a failed export trigger the FFmpeg fallback", which is the right policy for a name nobody recognises and the wrong one for a name recognised one file over. A device without the matching decoder now sends those four to FFmpeg up front instead of spending a doomed hardware attempt to discover it. No input loses hardware it could have used: each alias resolves to the MIME its canonical spelling already resolved to, so a device that has the decoder still answers true. `ConversionRouterTest` still passes and that is not evidence either way -- every `canDecode` in it is a hand-written stub that never reaches this table. #74 is the same family one level down. `describeVideo` answered "Unrecognised" for `InputProbe.UNPARSEABLE` and `describeAudio` had no such arm, so an unparseable audio codec would have fallen through to `?: name` -- and the sentinel opens with a NUL, so the source-info card would have rendered a `Text` beginning with U+0000. The two now share one body, which is what stops the next arm being added to one side only. Two corrections to that ticket, taken from the file rather than from the ticket, since it warns about exactly this: - It quotes `audioFromName` as opening with `null, InputProbe.UNPARSEABLE -> null`. It did not; it opened with `null -> null` and the sentinel reached `else`. Naming the sentinel in the shared lookup therefore changes no answer and is documentation, not the fix. - It says `describeVideo`'s arm has no test of its own. It did -- `descriptions stay readable for unknown and missing codecs` asserts it -- so deleting the shared arm now reddens three tests across both sides, not one. Mutations run, each on the full 386-test suite: add "avc3" to CodecNames only -> CodecVocabularyTest red on two counts, CodecNamesTest green: 8 tests, 0 failures, which is the ticket's point about per-table arm tests delete the UNPARSEABLE arm -> CodecNamesTest red on three, one of them quoting the NUL back add "x265" to DECODE_ONLY_NAMES -> CodecVocabularyTest red on the escape hatch delete "vp09" from the MIME map -> CodecVocabularyTest red on three, which is the state this commit is fixing Audio is not cross-checked, and that is a gap rather than a decision: the device capability check is video-only, so this module has no second audio table to compare `AUDIO_ALIASES` against. `Media3Engine.audioMimeTypeFor` is the other half and belongs to #85. `MediaProbe.shortName` (#84) is the fourth table and is untouched here for the same reason. Closes #87. Closes #74. 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 after a restart.
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.