MP3 to MKV

To convert MP3 to MKV, first choose your bitrate from the Bitrate dropdown (96k, 128k, 192k recommended, 256k or 320k), then drag and drop your MP3 files onto the drop area or click it to select them, and conversion to MKV starts automatically with each finished file appearing in its own row. Set the bitrate before adding files, since it is read the moment each file converts. You can add several MP3 files at once, and everything runs in your browser with a WebAssembly build of FFmpeg, so nothing is uploaded. Each row shows the new filename, its size, an inline preview player and a Download button.

Some extra quality is lost, because this is a lossy-to-lossy re-encode. Your MP3 is already a compressed, lossy file, and the audio track written into the MKV is encoded again with a lossy codec, so a little more detail is discarded and cannot be recovered. Converting to MKV never restores or improves what the MP3 already threw away. To keep the added loss as small as possible, choose a bitrate at or above your source MP3's bitrate, ideally 256 or 320 kbps.

People convert MP3 to MKV when a tool, editor, media server or pipeline expects a Matroska container rather than a bare MP3 file. MKV is an open, royalty-free container, so an audio-only MKV is simply your existing audio track wrapped inside a Matroska file instead of an MP3 wrapper. If all you want is a small, universally playable file, leaving it as MP3 or converting to AAC is usually the more compatible choice, since audio-only MKV is a niche need.

It is completely free and completely private. There is no signup, no account, no watermark and nothing to install, and because the conversion happens inside your own browser with WebAssembly, your MP3 files are never uploaded to any server. That makes it safe for confidential recordings such as interviews, client work or unreleased tracks, since the audio never leaves your device.

There is no size limit imposed by this site, because nothing is uploaded — the only real limit is your own device's memory. MP3 files are already compressed and fairly small, so most convert quickly, even in batches. Very large files of several hundred megabytes can still be slow or run out of memory on a phone, so use a desktop browser for those.

192 kbps is the default and a sensible balance of quality and size for most music and voice. Since your source is already a lossy MP3, choosing a bitrate at or above the MP3's own bitrate — often 192, 256 or 320 kbps — keeps the extra re-encoding loss minimal. Dropping to 96 or 128 kbps makes smaller files for speech or podcasts, but going below the source bitrate adds audible loss with little benefit.

Yes, it works in any modern browser on Windows, Mac, Linux, iPhone and Android — there is no app to install and no desktop software needed. The first conversion downloads the converter itself, a one-time file of about 32 MB, which your browser then caches, so later conversions start instantly. On phones, stick to shorter files or smaller batches, since very large audio can exhaust mobile memory.