How to use it
- Choose or drop a MP4 file.
- Choose the output format, codec and available bitrate settings.
- Convert, review the result, then download your file.
When to convert MP4 to MKV
MP4 names a container, not a codec. It may contain H.264, H.265, AV1 or other video and several audio formats. Read the detected source tracks before deciding whether to keep or change them.
MKV can hold many video and audio codecs. It is useful for keeping compatible encoded tracks in a different container. Many browsers and social platforms cannot play or accept MKV directly. Download it for a player or editor that supports Matroska.
Common questions
Is it free without an account?
Yes. There is no signup, watermark, or charge to download. Your browser does the processing.
Which tracks are kept?
The primary video and audio tracks are used, except when you choose Remove audio. Extra tracks, subtitles and attachments are omitted. Unsupported selected tracks produce an error instead of silently disappearing.
Why is a codec missing or a conversion blocked?
Codec support depends on your browser, operating system, device and source profile. The menus list available output encoders, and conversion checks the actual source. Try a current Chrome or Edge browser, another format, or Keep source codec for a compatible container.
Does conversion always preserve quality?
Keeping compatible encoded tracks avoids recompressing them. Re-encoding with a lossy codec can reduce quality. Lossless output preserves decoded samples but cannot recover detail lost in an earlier encoding.