JMR-dev
47a423413b
README promised, without qualification: "Conversions run as durable background work, so they survive leaving the app and are restored after a restart." The first half is true and the reattachment work made it truer. The second half has one exception the sentence does not admit, and it is the case a user is most likely to hit without understanding it. When Android refuses a foreground-service start, FailureOutcome retries -- ten attempts on the default exponential backoff, 30 s doubling to a five-hour clamp, about eight and a half hours in total -- and then returns FOREGROUND_DENIED on a FAILED job. Reattachment excludes FAILED (Reattachment.kt:176). So the job is not restored, and neither is the message explaining why: the user opens the app to an empty screen. FailureOutcome's own KDoc already says this plainly -- "a user who was not watching when the eleventh attempt ran will find an empty screen rather than the explanation". The code was honest and the README was not, which is the wrong way round for the two documents. The replacement says what actually happens and ends with the thing the user can act on: reopening the app is what grants permission to run, so a conversion stalled this way should be started again rather than waited on. That is the same reasoning FOREGROUND_DENIED_MESSAGE is written on -- "open the app and start it again" is the fix, not filler. Deliberately not claimed: that the app tells you. It does not, and #16 is the open ticket for giving a present, willing user a way to make that retry happen now. Writing "you will be told" here would be the same defect this commit is fixing, one release earlier. Verified against the current code rather than the finding's date -- R35 was filed as PLAUSIBLE on 2026-08-22 and both mechanisms it names are still in place. Closes #44.
176 lines
8.7 KiB
Markdown
176 lines
8.7 KiB
Markdown
# LibreMediaConverter
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A free and open-source media converter for Android — batch video transcoding and
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compression, audio extraction and conversion, GIF and frame export, and file merging.
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Android 13+ (API 33). Built with Jetpack Compose and Material 3.
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> **Status: working, unreleased.** Both conversion engines, the router, the background
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> job queue and the join flow are implemented and building. The FFmpeg format tests run
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> green on a physical Pixel 10 Pro XL (API 37) and on local emulators at API 33–36, and
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> CI runs the instrumented suite at API 33–36 on every pull request.
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*Correction (`R18 / #27`, 2026-08-22): this line used to say the FFmpeg format tests had "been
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written but not yet executed on a device" — true when written, false from the first device pass,
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and never updated. `FFmpegEngineTest`'s nine format tests were in every run named above and none
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of them failed; the runs are recorded under "Verified on real API 37 hardware" in
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[`docs/api-37-emulator-crash.md`](docs/api-37-emulator-crash.md) and "The sweep, run" in
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[`docs/local-emulator.md`](docs/local-emulator.md). API 37 has no CI row — that emulator image is
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broken — so it stays a manual Pixel check before each release.*
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## Licensing at a glance
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- **Source code: MIT**
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- **Distributed APK: GPL-3.0** — because it bundles FFmpeg built with x264/x265
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That split is deliberate, not an oversight. See [`LICENSES/README.md`](LICENSES/README.md)
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for the reasoning and the corresponding-source obligations.
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## Architecture
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Two conversion engines behind an explicit router, because neither one covers the job alone.
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### AndroidX Media3 Transformer — the hardware path
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Handles the common cases: H.264/HEVC, resolution and frame-rate changes, rotation,
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overlays, and audio to AAC. Fully hardware accelerated end to end — MediaCodec decodes to
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a GL surface and MediaCodec re-encodes, so frames never round-trip through the CPU.
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Roughly 7–8× realtime on 720p.
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It writes **MP4 and nothing else**. `media3-muxer` ships WebM, Ogg, WAV and AAC muxers too,
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but none can be driven by Transformer — they throw from `addMetadataEntry`, which the muxer
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wrapper calls for every metadata entry a real recording carries. It *reads* far more than it
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writes, Matroska included, which is what makes MKV → MP4 a hardware remux.
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### FFmpeg — the long tail
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Everything Media3 structurally cannot do:
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- Containers outside MP4/WebM/Ogg/WAV/AAC — MKV, MOV, AVI, FLV, MPEG-TS, WMV/ASF
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- **MP3 output** — Android has no MP3 encoder at any version; this is a platform gap
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- GIF and image sequences
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- Input codecs with no platform decoder on the device
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- CRF and 2-pass rate control, for the quality tier
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- Codecs Media3's muxers decline even on a stream copy — its MP4 muxer carries AAC, Opus,
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Vorbis and PCM, but neither MP3 nor FLAC
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### Quality tiers
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The router is surfaced to users as a quality choice rather than hidden:
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| Tier | Engine | Rate control | Trade-off |
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|---|---|---|---|
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| **Fast** (default) | Media3 / MediaCodec | bitrate-targeted | ~7–8× realtime, low battery cost |
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| **Best quality** | FFmpeg + x264/x265 | CRF or 2-pass | ~realtime or slower, better quality per byte |
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## A note on "GPU acceleration"
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Android has **no GPU video codec path**. There are three distinct tiers, and conflating
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them causes a lot of confusion:
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1. **Fixed-function video codec silicon** — reached through `MediaCodec`. This is what
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"hardware accelerated" means for encode and decode. It is not the GPU.
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2. **GPU shader cores** — genuinely used, but only for filters, scaling, and color
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effects on already-decoded frames, via OpenGL ES. Never for entropy coding.
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3. **CPU** — x264, x265, and software decoders.
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FFmpeg's `-hwaccel` is meaningful on Android only as `mediacodec`, and even then it
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targets direct-to-Surface playback rather than file-to-file transcoding. Vulkan Video
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exists in FFmpeg 8.0+ but no shipping Android GPU driver exposes it — no `VK_KHR_video_*`
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extension appears in any Android Vulkan Profile tier.
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So this app is hardware accelerated via MediaCodec, and GPU accelerated for effects via
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GL shaders. Both are real; neither is "the GPU decoding video."
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## Remuxing
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Changing the container without touching the streams. Copying an H.264 track from MKV into
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MP4 moves the same samples into a different wrapper: it finishes in seconds instead of
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minutes, costs no quality, and needs no encoder — which is why it stays on the hardware
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path even on a device that cannot encode the codec in question.
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`Copy` is a codec choice like any other, so it can be mixed: copy the video and re-encode
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only the audio, or the reverse. Picking a codec the source already uses is upgraded to a
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copy automatically **when the container is changing** — if container and codec both already
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match, the only reason to run the job is to re-encode it, so it does.
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A copy is never attempted on a stream whose codec could not be identified. A needless
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re-encode costs time; a wrong stream copy costs a file that will not play.
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## Features
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| | Formats |
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|---|---|
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| Video out | MP4, MOV, MKV, WebM, MPEG-TS, AVI, FLV, WMV/ASF |
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| Video codecs | H.264, H.265, VP9, or copy the source stream |
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| Audio out | MP3, AAC/M4A, FLAC, Opus, WAV, MKA |
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| Audio codecs | AAC, Opus, MP3, FLAC, PCM, or copy the source stream |
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| Images | GIF, PNG frame sequences |
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| Other | Remux without re-encoding; join several files into one |
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Presets cover the common combinations in one tap. The Advanced picker exposes the full
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container × codec matrix — including combinations that cannot work, which it explains and
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offers alternatives for rather than hiding.
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Conversions run as durable background work, so they survive leaving the app and are
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restored when you reopen it.
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One case is not restored, and it is worth knowing about. If Android refuses to let a job
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restart in the background, it is retried on an exponential backoff for about eight and a
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half hours and then given up on — and a job that has been given up on does not come back
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when you reopen the app. Reopening the app is what grants permission to run, so a
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conversion that has stalled this way is best started again from the app rather than waited
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on.
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## Building
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Requires the Android SDK with API 37. **Do not pick a JDK** — the repo does.
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`gradle/gradle-daemon-jvm.properties` pins the daemon to Java 25 and carries foojay
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download URLs per platform, so Gradle finds an installed Java 25 or downloads one on the
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first build, whatever `JAVA_HOME` points at. `JAVA_HOME` only chooses the *launcher*, which
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Gradle 9.7.1 will run on Java 8 or newer. Everything the build actually compiles is Java 25,
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the app's own bytecode included. `./gradlew --version` prints the launcher and the daemon
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separately, and they routinely differ.
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FFmpeg is committed as a prebuilt archive under [`bin/`](bin/README.md), so a clone
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builds without a cross-compile. That is deliberate: rebuilding it per CI run made test
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results ambiguous, because a red build could mean broken code or a build that hiccuped.
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See [`bin/README.md`](bin/README.md) for its provenance and how to regenerate it.
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```sh
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./gradlew :app:assembleDebug # debug APK
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./gradlew :app:testDebugUnitTest # JVM tests
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./gradlew :app:connectedDebugAndroidTest # device tests, needs a running device
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./gradlew :app:assembleRelease # R8-minified release
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```
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See [`tools/ffmpeg/README.md`](tools/ffmpeg/README.md) for why the build is
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containerised and which flags matter. That recipe remains the authority — the committed
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archive is its output, and is also what satisfies the GPL corresponding-source
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obligation.
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## Testing
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Unit tests cover the parts that decide correctness without needing hardware: the routing
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matrix, the container × codec capability matrix, the FFmpeg argument builder, and both
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stream-copy-versus-re-encode planners. They run against fabricated device profiles, so
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branches like "this device cannot encode HEVC" are reachable regardless of what the test
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machine is.
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Instrumented tests cover the parts that only a device can prove: real hardware
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transcoding, the foreground service type, and each FFmpeg output format asserted against
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the produced file rather than the exit code. The remux tests additionally assert which
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*engine* ran — a stream copy produces an identical file either way, so an output-only
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assertion cannot tell a hardware transmux from FFmpeg's `-c copy`.
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## Privacy
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The app has **no `INTERNET` permission**, so it cannot open a network connection at all.
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Nothing is uploaded, and there is no analytics or advertising. See [PRIVACY.md](PRIVACY.md),
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which also explains the permissions WorkManager adds automatically.
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## Contributing
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Contributions are welcome. Note that contributions to the source are under MIT, while
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the distributed binary remains GPL-3.0 for the reasons described in `LICENSES/README.md`.
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