MKV is a flexible open container popular for high-quality movies and anime, but native MKV playback is patchy outside VLC. Repackaging to MP4 keeps the same video stream and lets virtually any device play it.
Convert MKV to MP4 – Free Online MKV to MP4 Converter
Why convert MKV to MP4?
- Stream from your library to smart TVs, Apple devices, and game consoles.
- Upload to YouTube, Vimeo, and social platforms that don't accept MKV.
- Edit in software that lacks full MKV support (Final Cut, Premiere consumer).
Tip: When video is already H.264/H.265 and audio is AAC, the conversion is lossless (rewraps streams). Mixed codecs (DTS audio, MPEG-2 video) require re-encoding.
What is the difference between MKV and MP4?
| MKV | MP4 | |
|---|---|---|
| Container origin | Matroska, an open community project from 2002 | ISO standard container backed by the MPEG group |
| Typical codecs inside | H.264/H.265 video; AC-3, DTS, or FLAC audio; soft subtitles | H.264/H.265 with AAC audio, at most limited subtitle support |
| Track flexibility | Unlimited audio, subtitle, and attachment tracks | Usually one video and one audio track in practice |
| Device support | Good in VLC, Plex, and recent TVs; absent on many devices | Plays on essentially everything made this century |
| Best for | Archiving movies with subtitles and multiple languages | Playback, uploading, and sending to other people |
Does converting MKV to MP4 lose quality?
Whether this conversion touches your picture depends entirely on what the MKV holds. H.264 or H.265 video moves into MP4 as-is — same resolution, same frames, near-identical file size. The audio side is where re-encoding most often happens: DTS and FLAC tracks, common in movie rips, have no standard place in MP4 and get transcoded to AAC, an audible-in-theory but rarely noticeable change on TV speakers.
Multi-track MKVs get flattened. Expect the output to carry a single audio track — normally whichever the file marks as default — and expect soft subtitle tracks to disappear, since MP4's subtitle story is weak and inconsistently supported by players. Chapters and cover-art attachments are also left behind. The video stream itself is never downscaled; a 1080p MKV yields a 1080p MP4.
Size stays roughly flat on a remux and changes only modestly when audio is transcoded. If your output is dramatically smaller than the source, the video was re-encoded — worth knowing if the MKV is your only copy, in which case keep it.
What can go wrong converting MKV to MP4?
- The MP4 came out with the wrong audio language — Multi-language MKVs convert with the track flagged as default, which is not always the one you want. Set the desired track as default in a tool like MKVToolNix first, then convert.
- My subtitles are gone in the converted file — That is expected — MKV soft subtitles don't carry into MP4 reliably. Extract them to an .srt with a subtitle tool and load that file in your player next to the MP4.
- My movie file is far over the 50 MB free limit — Feature-length MKVs run into gigabytes, well past the free tier's 50 MB cap. The online route suits clips, episodes trimmed to a scene, or short recordings; for full movies use a desktop tool like HandBrake.
- The MP4 stutters on my TV even though the MKV played on my PC — If the source was H.265 at a high bitrate, some older TVs decode it poorly regardless of container. Try playback from a USB stick rather than DLNA streaming, or test on another device to isolate the bottleneck.
How to convert MKV to MP4
- Upload your MKV file using the area above.
- MP4 is preselected as the target format.
- Click Start and wait for the conversion to finish.
- Download your converted MP4 file.