How MediaConverter.io converts files without uploading them

A normal online converter uploads your file to a server, converts it there and sends the result back. MediaConverter.io skips the round trip: the conversion code is downloaded to your browser like any other part of the page, and your device does the work.

1. 1On your device

   You choose a file

   Dropping a file on the page, or picking it with the file dialog, lets this browser tab read that one file. Nothing is copied to a server.

2. 2In your browser

   The page reads it

   The tool inspects the file right there in the tab: its format, codecs, duration, resolution and audio or subtitle tracks.

3. 3On your device

   Your device converts it

   Your browser's built-in media engine, or a copy of FFmpeg running inside the page, decodes the file and encodes it into the new format.

4. 4On your device

   You save the result

   The finished file goes from the tab's memory straight to your browser's downloads. Close the tab and anything not yet saved is gone; there is nothing to delete on our side.

Privacy. Your recording, film or voice memo stays on your device. There is no copy on our servers to leak, to be kept longer than you expected or to delete afterwards. Like most websites we measure how the site is used, with Google Analytics and Microsoft Clarity: pages visited, clicks, and events such as which formats were converted and the file size rounded to the nearest megabyte. Those tools never receive the file itself.

Speed. There is no upload to wait for and no download of the result, which on a large video can take longer than the conversion. How fast the conversion itself runs depends on your device. When your browser can use the video hardware built into your computer or phone, it is quick; when the tool has to fall back to FFmpeg, the processor does all the work and it is slower.

Limits. Because everything happens in your device's memory, the practical limit is how much memory your browser can use, not a number we set. The converters load the whole source file into memory (the FFmpeg engine they use is itself capped at about 2 GB), so roughly 2 GB per file is the practical ceiling and larger files may fail to open. Phones have less memory and slower processors than computers, so they take longer and reach that limit sooner. Keep the tab open until the conversion finishes; closing it stops the conversion and discards the result.

Reading the file. A file you pick is exposed to the page as a browser File object. Inspecting it happens in place: mediabunny pulls only the byte ranges it needs, and FFmpeg's ffprobe reads the file details through a lazy mount instead of copying the file. The conversion steps that use FFmpeg then copy the whole file into FFmpeg's memory, which is where the roughly 2 GB per-file ceiling comes from.

The fast path: WebCodecs. WebCodecs is a browser API that gives web pages direct access to the video and audio decoders and encoders the browser already ships, which can use your device's video hardware where it is available. The tools drive it through mediabunny, an open-source TypeScript library that reads MP4, MOV, Matroska (MKV and WebM), MPEG-TS, WAV, Ogg, FLAC, MP3 and ADTS AAC files, feeds the frames through WebCodecs and writes MP4, MOV, MKV, WebM and the common audio containers.

The fallback: FFmpeg compiled to WebAssembly. For everything the fast path cannot do, the page runs ffmpeg.wasm, the FFmpeg 0.12.10 core compiled to WebAssembly. It is served from our own domain (not a third-party CDN), runs single-threaded on the processor, and is only used for what WebCodecs cannot do: writing AVI, FLV and TS files and reading FLVs (it moves the picture between containers rather than encoding it), converting AVI files and video your browser cannot decode (DivX, Xvid, MPEG-2 and similar), and encoding most audio formats. It is slower than WebCodecs but works the same in every browser.

Choosing a path. Before converting, the Video Converter and Video Compressor ask mediabunny whether it can open the file, decode its video and write the target format. If any answer is no, or if the browser would have to drop the video track, the whole job goes to FFmpeg instead, so an unsupported codec means a slower conversion rather than a broken file.

The result. The converted file is assembled in memory and handed to your browser as a local blob: link, which is what ends up in your downloads folder. When a tool offers "Download All", the ZIP is built in the page as well.

The free tools listed below, and every format-to-format page such as MP4 to MP3, process files only on your device. Our servers deliver the web pages, the tool code and the FFmpeg engine, the same as for any website.

Two features work differently, and are separate from the converter tools this page describes:

• The AI Studio (our AI assistant, also offered as ToolGPT) sends your chat messages to AI models running on servers. Most of its file work runs in your browser like the tools here, but noise removal and voice or music separation run on a cloud service: after you allow it, the audio is uploaded for processing.
• Automatic subtitles in the timeline video editor send the project's audio to a transcription service to produce the captions.

• Video Converter →Change the format, codec, resolution or frame rate of a video.
• Audio Converter →Convert between MP3, WAV, FLAC, M4A, AAC, OGG and more.
• Video Compressor →Shrink a video to a target size or bitrate.
• Video Cut & Trim →Keep or remove a section of a video.
• Video Splitter →Split one video into several clips.
• Video Rotator →Rotate or flip a video.