JMR-devandClaude Opus 5
0c352cdcfb
Adds the second engine and the rules that choose between them, turning a
video transcoder into a converter.
The router encodes capability boundaries, not preferences. Media3 handles
what it genuinely can and FFmpeg takes the rest:
MKV, and any container Media3 cannot mux
MP3, which Android cannot encode at any API level -- a platform gap
rather than a Media3 limitation
GIF and PNG frame sequences, which have no Media3 muxer
VP9 and AV1 targets: Transformer.setVideoMimeType accepts only
H.263/H.264/H.265/MP4V, so the WebM muxer has no encoder behind it
inputs with no platform decoder, since Transformer ignores ExoPlayer's
bundled software decoders and the dav1d extension does not rescue it
the Best quality tier, because CRF and two-pass come from x264/x265 and
no Android hardware encoder exposes either
Rule order matters and is deliberate: specific reasons are checked before
general ones because the reason is shown to the user. "Android has no
encoder for this format" is actionable for MP3; "this container needs
FFmpeg" is not. A test caught the original ordering getting this backwards.
Hardware support is vendor-declared and, per the platform's own docs,
"cannot be tested for correctness", so the static rules are backed by a
dynamic fallback: a Media3 export that fails is retried on FFmpeg rather
than surfaced as a failed conversion.
Joining files chooses between a stream copy and a re-encode by inspecting
the inputs. The concat demuxer requires matching codec, resolution and
timebase, and does not reliably fail when they differ -- it can emit a file
whose later segments are garbled. Unknown properties count as a mismatch,
because two nulls are not evidence of agreement.
The UI surfaces the routing decision rather than hiding it, so a slow job
explains itself, and offers a per-job engine override.
Navigation is adaptive: a bottom bar on phones, a side rail on wider
screens. Not cosmetic -- from targetSdk 37 Android ignores screenOrientation
and resizableActivity on displays at least 600dp wide, with no opt-out, so
the app is resized whether or not it is ready.
62 unit tests cover the routing matrix, the FFmpeg argument builder and the
concat planner on the JVM, against fabricated device profiles so branches
like "this device cannot encode HEVC" are reachable without that hardware.
Device-level tests for the FFmpeg formats are written but not yet run; the
emulator in this environment will not stay up.
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.