ZenConverter is a local-first file converter for Android, written in Kotlin with Jetpack Compose, for people who want to convert video, audio, and image files on their own phone instead of uploading them to someone else's server.

What it is

ZenConverter is a native Android application built with Kotlin and Jetpack Compose, using Material 3 and a foreground service pipeline for longer conversion jobs. File access goes through Android's Storage Access Framework, so the app works on files the user picks rather than scanning storage. It is licensed under AGPL-3.0, and its topic list places it among Android apps, FFmpeg-based conversion tooling, and local-processing utilities.

The concrete problem it solves is the shape of most Android converter apps. The README describes them as cluttered, ad-heavy, oddly priced, or built around uploading a file somewhere before any conversion happens. ZenConverter removes that: no ads, no accounts, no paywalls, no remote uploads, and the INTERNET permission is used only for manual update checks and on-demand model and font downloads. Supported routes are verified on a physical Android device, and their known limits are written down in a public support matrix at formats/support-matrix.md rather than hidden.

Key capabilities

• FFmpeg true video and audio re-encoding for MP4, MKV, and MOV outputs, including MP4-to-MP4, with adjustable codec, bitrate, resolution, frame rate, audio settings, draggable quick trimming, multi-point splitting, and compression presets that fix the CRF, the video quality and size strategy, and the AAC audio bitrate; video merge concatenates multiple files with aspect-ratio normalization and audio stream handling.
• Contact sheets exported as JPG or PNG over 3×3, 3×4, 4×4, or 5×5 sample grids, with an optional metadata header and timestamp badges.
• Animated GIF export on a palette-based FFmpeg path that automatically takes at most the first 30 seconds, 30 fps, and 900 frames, with a default 480 px short-side cap plus 720 px and Original options.
• Audio extraction and conversion to MP3, M4A, WAV, FLAC, WMA, and OPUS, all through FFmpeg true audio re-encoding, with bitrate, sample-rate, channel, and encoder checks wired in; OPUS resamples to standard sample rates.
• Advanced processing: video reverse playback, fade, mirror, rotation, and frame fit or crop; audio reverse, non-model afftdn noise reduction, fade, volume and mute, and echo.
• Image conversion across JPG, JPEG, JFIF, JPE, PNG, WEBP, GIF, HEIC, HEIF, and ICO inputs, with JPG, JFIF, PNG, WEBP, ICO, and PDF outputs; GIF can use its first frame or split frames into a folder.
• Task queue with direct share and open import, gallery and folder batch import, mixed-file routing, per-file target selection, per-task progress and failures, cancellation, and output sharing.

Who uses it and how

• Individual Android users who convert files on the device and want no account, no ad, and no upload step anywhere in the path.
• People working with large videos, which the README treats as real use cases; these need adequate free storage, memory, and power, and the device must stay available while a long foreground conversion runs.
• Batch workflows that start from the gallery or a folder, configure same-type batch options, route mixed file types, and choose targets per file.
• Sharing workflows that begin in another app: direct share or open import, then output sharing and best-effort opening of the result or its location.
• Multilingual users, with in-app language switching for English, Simplified Chinese, Traditional Chinese, and French, alongside Material You dynamic colors, dark mode, and an independent OLED black toggle.

Getting started

The provided README names no package, Docker image, or compose file; ZenConverter ships as a native Android app built with Kotlin and Jetpack Compose, and the listed project homepage is https://zenconverter.xlab.my. The support matrix at formats/support-matrix.md is the reference for which routes are Stable, Beta, or Experimental.

How it compares

No competing product is named in the facts provided, so ZenConverter stands alone in this registry. Its README frames it against desktop open-source converters, which it says are plentiful and good, and against Android converters that are cluttered, ad-heavy, oddly priced, or built around uploading a file first.

When to use it — and when not to

There is no database, object store, or SMTP service to operate, but the app leans on the phone: large conversions need free storage, memory, and power, and a running foreground job ties the device up. Users who need HEIC and HEIF handling independent of the device decoder, GIF export beyond the first 30 seconds, or reliable 2× frame interpolation across every chipset should not pick it — that route uses Tencent NCNN Vulkan with RIFE, performs on-demand model downloads with SHA-256 verification, and stays experimental because mobile GPU drivers and memory vary. Reverse playback also carries conservative safety limits, so it is not a general-purpose reverse tool.

flowchart LR
    Pick["Add files"]
    Configure["Configure each task"]
    Queue["Ready queue"]
    Service["Foreground service"]
    Engine["FFmpeg / Native / Office / WOFF2 / NCNN"]
    Output["Save output"]

    Pick --> Configure --> Queue --> Service --> Engine --> Output