Nothing gets uploaded. Videos are processed locally in your browser.
No fixed server upload limit. Your device’s available memory and browser determine the practical limit.
The video engine downloads about 31 MiB on first use. One video runs at a time. Current WebAssembly inputs must be smaller than 2 GiB; practical limits are often much lower. Google advertising may make separate network requests; file bytes and names are never passed to it. FFmpeg licenses and source.
Produce a web-oriented copy of a Matroska file
Although WebM is related to Matroska, changing the extension is not sufficient. The video is encoded as VP8 and the first audio track as Vorbis, with additional tracks and subtitles omitted.
Understanding MKV and WEBM
Matroska (MKV) can hold several video, audio and subtitle tracks in a single container. Conversion here selects the first video and first audio track; it does not preserve the complete track collection.
WebM is a web-oriented container commonly carrying VP8 or VP9 video and Vorbis or Opus audio. It is often produced by browser recording tools and screen recorders.
Compatibility after conversion
VP8 + Vorbis for web playback; older Apple software may need MP4. Test the downloaded file in its intended application. Browser preview support and container conversion support are different capabilities.
Quality, time and practical limits
Start with Auto and Original resolution for a general playback copy. High uses more bits to retain detail; Smaller File trades some detail for space. A long or high-resolution recording can take longer than its running time, particularly on a phone. This version does not preserve HDR mastering metadata, subtitles or multiple audio tracks. Keep your original before evaluating a conversion.
Local processing you can verify
Open your browser’s Network panel before selecting a video. You will see engine and page downloads, anonymous tool usage events, and separate ad requests, but no request carrying the video or its filename. Cancel terminates the worker; clearing the batch releases retained results. More about privacy verification.
Choose a local file, wait for its metadata, select the output and quality, then convert and download. A batch is processed one video at a time. The engine downloads on first use; your videos do not upload.
What will the WEBM file contain?
VP8 + Vorbis for web playback; older Apple software may need MP4. Only the first video and audio tracks are selected. GIF has no audio; subtitles, chapters and metadata are not copied.
Will the quality and file size stay the same?
Video is re-encoded, which can change quality and size. High quality usually retains more detail and uses more space. Original resolution avoids intentional resizing, though odd dimensions round down for codec compatibility. Keep the source as your master copy.
How long does conversion take, and how large can my file be?
Time depends on duration, resolution, codec and device. Browser WebAssembly can be slower than a desktop encoder. There is no fixed server upload limit; device memory sets the practical limit. The current engine requires inputs below 2 GiB, and phones often need much smaller clips.
Does FormatPlease upload or store my video?
No. File bytes and names stay on your device. The browser downloads the engine from this website and runs it in a worker. Separate advertising requests may occur, but the converter does not provide your files to advertising or analytics.
Why might a MKV file fail?
A container extension does not identify every codec inside it. Unsupported codecs, encrypted files, damaged containers and memory pressure can prevent conversion. There is no server upload fallback; try another source or a shorter clip.
