android-transcoder
Video transcoding on android
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Recording Compressor #

CI

Android app that records the screen and compresses recordings on-device with FFmpeg or the device encoder (Media3 Transformer).

  • Kotlin, Jetpack Compose, Material 3
  • Import a video or audio file via the system file picker, or share / send one (or several) from another app
  • Combine a picture or video with a separate soundtrack (FFmpeg or Media3). A still image lasts as long as the audio. Home and Share both accept several pictures/videos plus several audio files in one pick and create one job per pair.
  • Clear all Recent / Library jobs and leftover cache files (gallery outputs stay)
  • Audio-only output: extract a video soundtrack or transcode audio to AAC (.m4a) or Opus (.webm) with FFmpeg or Media3
  • WebM output: VP8/VP9/AV1 + Opus video, or Opus-only audio, on both engines
  • AV1 on both engines when the device has an AV1 encoder; FFmpeg can also use libaom-av1 / libsvtav1 if the bundled build includes them
  • Screen recording via MediaProjection (microphone, internal audio, or both mixed live) with pause/resume, countdown, max length, low-storage auto-stop, live region crop, grayscale, camera inset (front or rear), tap / laser / ink overlays, floating controls, Picture-in-Picture controls, and a Quick Settings tile. Internal audio can be limited to one app; mic device, echo cancel, noise suppress, gain, and ducking apply while capturing. Capture 30 or 60 fps, pick a bitrate, and write MP4 or WebM. Record already compressed (H.264/HEVC/AV1 or VP8 WebM) to skip the second encode pass. Bookmarks can become chapters or split jobs.
  • Presets plus advanced encoder settings, including a grayscale filter on FFmpeg and Device (Media3)
  • Named compression profiles: save the current Compress options and load them later from a dropdown
  • Optional on-device captions: Whisper tiny via sherpa-onnx, muxed as a subtitle track plus an .srt sidecar. Optional burn-in paints each cue onto the frames at its Whisper timestamp (always visible; re-encodes the picture). The speech model downloads once (~100 MB) and audio never leaves the phone. A Transcribing notification shows progress; Cancel there skips captions and keeps the file.
  • Two encode engines: FFmpeg (default, with software fallback) or Device / Media3 (hardware MediaCodec, same approach as Compressor Edge)
  • Play-oriented: target API 37, scoped storage, typed foreground services, LGPL FFmpeg
  • Android 16 App Functions so a system agent can import, customize, start, wait, retry, share, and discard jobs (no media bytes)
  • Optional Device library access (READ_MEDIA_*) so that agent can list and import files already on the device without the picker
  • Settings hardware test: 1-second encodes on h264/hevc/vp9/av1_mediacodec and Media3 for max resolution, 10-bit HDR, and realtime speed

Build #

Requires JDK 17+ and the Android SDK (compile SDK 37).

export ANDROID_HOME=$HOME/Android/Sdk
./gradlew :app:assembleDebug :app:testDebugUnitTest

The debug APK is written to app/build/outputs/apk/debug/.

Release builds sign with KEYSTORE_PATH, KEYSTORE_PASSWORD, KEY_ALIAS, and KEY_PASSWORD when those env vars are set. Otherwise they read keystore.properties at the repo root (storeFile, storePassword, keyAlias, keyPassword). Plaintext release.jks and keystore.properties are gitignored. Encrypted copies in signing/ are committed; decrypt with SIGNING_PASSPHRASE (see signing/README.md). If the keystore file or passwords are missing, assembleRelease still succeeds and writes an unsigned APK.

./gradlew :app:assembleRelease :app:bundleRelease

The release APK is app/build/outputs/apk/release/ (app-release.apk when signed, app-release-unsigned.apk otherwise). The Play upload is app/build/outputs/bundle/release/.

CI #

GitHub Actions (.github/workflows/ci.yml) runs on master, pull requests, and manual dispatch. It uses JDK 17, installs Android SDK 37, then runs assembleDebug, testDebugUnitTest, lintDebug, and assembleRelease. On master and workflow_dispatch it decrypts signing/*.enc with the SIGNING_PASSPHRASE repository secret, signs the release APK/AAB, and uploads them as the app-release artifact. Pull requests stay unsigned so fork PRs never see the key. Device checks in docs/manual-qa.md stay manual.

App Functions (Android 16+) #

Privileged system agents can drive imported jobs without opening the UI. The service is com.androidcompress.app.agent.CompressAppFunctionService (.debug in debug builds).

Typical tools: describeCapabilities, compressNow, waitForJob, waitForQueue, listDeviceMedia, importDeviceMedia, importDeviceMediaBatch, importCombineDeviceMedia, updateJobSettings, previewEncode, startJob, retryJob, cloneJob, getProgress, shareOutput, openOutput, discardJob, requestLibraryAccess, getEncoderCapabilities, getSourceInfo.

adb shell cmd app_function list-app-functions | grep -A 20 androidcompress
adb shell "cmd app_function execute-app-function \
  --package com.androidcompress.app.debug \
  --function 'com.androidcompress.app.agent.BaseCompressAppFunctionService#describeCapabilities' \
  --parameters '{}'"

Grant Device library access in Settings (Allow all) so listDeviceMedia / compressNow can open files already on the device. requestLibraryAccess opens that prompt. Without the grant, import still works from the picker or Share. Functions return job metadata, not media bytes. waitForJob blocks at most 180 seconds; call it again if timedOut is true. Gemini-as-caller is still a platform preview; you can test with adb or the official App Functions testing agent.

PowerShell helper (Windows). Finds adb.exe from ANDROID_HOME / ANDROID_SDK_ROOT, local.properties, or %LOCALAPPDATA%\Android\Sdk\platform-tools:

# After granting library access on the phone:
.\scripts\test-app-functions.ps1
.\scripts\test-app-functions.ps1 -Query clip
.\scripts\test-app-functions.ps1 -LocalFile C:\Videos\clip.mp4
.\scripts\test-app-functions.ps1 -Path /sdcard/Download/clip.mp4 -Preset SMALLER -Container WEBM
.\scripts\test-app-functions.ps1 -RelativePath Download -Kind VIDEO

Automation (Tasker / MacroDroid / adb) #

Exported receiver com.androidcompress.app.agent.AutomationReceiver. Send an explicit broadcast to this app’s package (com.androidcompress.app or com.androidcompress.app.debug):

Action Effect
com.androidcompress.app.automation.COMPRESS Import + start encode (uri, path, or intent data). Optional extras: preset, engine, container, codec, output, requestId, replyPackage, …
com.androidcompress.app.automation.RECORD_STOP Stop the active screen recording. Does not start capture.
com.androidcompress.app.automation.CANCEL_QUEUE Cancel the running encode and every queued job.

When the work finishes, the app broadcasts com.androidcompress.app.automation.COMPLETED (status, jobId, outputUri, error, requestId, …). Listen for that instead of polling. Paths need Device library access.

adb shell am broadcast -p com.androidcompress.app.debug \
  -a com.androidcompress.app.automation.COMPRESS \
  --es path /sdcard/Download/clip.mp4 --es preset SMALLER --es requestId t1
adb shell am broadcast -p com.androidcompress.app.debug \
  -a com.androidcompress.app.automation.RECORD_STOP
adb shell am broadcast -p com.androidcompress.app.debug \
  -a com.androidcompress.app.automation.CANCEL_QUEUE

FFmpeg #

Day-to-day builds use dev.ffmpegkit-maintained:ffmpeg-kit-full:8.1.7 (FFmpeg 8.1.2, 16 KB pages, arm64-v8a, LGPL — no x264/x265). A Play Store binary can stay on that AAR or be rebuilt from FFmpegKitNext — see docs/ffmpeg-build.md.

License #

This project's source is licensed under the MIT License. Bundled FFmpeg remains LGPL-3.0; see docs/ffmpeg-build.md.