Convert MKV to MP4
MKV holds the same video as an MP4 — it is only the wrapper that TVs, phones and iPads refuse. The video and sound are copied straight across, so a two-hour film is done in seconds and looks exactly as it did.
- Never stored
- No queue, no waiting
- No signup, no watermark
How it works
Add your MKV
Drop the file. You are shown what is inside: H.264 or HEVC video, and AAC, MP3, AC-3 or DTS sound.
Let it rewrap
The picture is copied without re-encoding. Dolby and DTS sound, which an MP4 player cannot handle, is converted to AAC.
Download the MP4
Plays on a TV, an iPad, a PlayStation and in every editor.
Usually a relabel, not a conversion
MKV is a container — a box that holds video, sound and subtitles — and so is MP4. What is inside an MKV is very often H.264 video with AAC sound, which is exactly what an MP4 is supposed to hold. When that is the case the picture and sound are moved across untouched, without being decoded or re-encoded at all: a two-hour film converts in seconds, loses literally nothing, and comes out about the same size. If your file converts almost instantly, that is what happened, and it is the best possible outcome.
When the contents are not MP4-compatible — VP9, or sound as Vorbis, FLAC or TrueHD — there is no way to avoid re-encoding, and then it takes real time and costs a generation of quality. The two cases feel completely different and it is worth knowing which you got.
MKV can hold things MP4 cannot, and that is what you lose. An MKV is frequently a whole release: several audio tracks for different languages and commentary, a stack of subtitle tracks, chapter markers, cover art, and even the font files needed to render styled subtitles correctly. MP4 accommodates one main video and one sound track here, so the first of each is kept and the rest are left behind — the page tells you when that happens rather than letting you discover it halfway through a film in the wrong language.
Subtitles deserve their own warning. MKV's usual subtitle formats — SRT and the styled ASS/SSA that fansubs use — have no proper home in an MP4, so they do not travel. If the subtitles matter, pull them out of the MKV first and keep them as a separate .srt beside the video, which every player and every TV will load.
When you want something else
ffmpeg does the same remux and keeps everything: ffmpeg -i in.mkv -c copy -map 0 out.mp4 carries every track across rather than the first of each, and -c copy guarantees no re-encoding. Adding -c:s mov_text converts subtitles into the one form an MP4 can hold. It is free, it handles a folder in a loop, and it has no memory ceiling.
Before converting at all, check whether you need to. VLC, MPV and every current smart TV play MKV directly, and the format is better than MP4 at nearly everything — the only real reasons to convert are an Apple device, an older games console, or a video editor that refuses it. Converting a file your player already handles costs time and gains nothing.
Frequently asked questions
Is it really lossless?
For the picture, yes: the encoded video is copied byte for byte into the new container, so it is identical. Sound is copied too when it is AAC or MP3; AC-3, E-AC-3 and DTS have to be converted, because MP4 players do not play them.
Why is it so much faster than other converters?
Because nothing is decoded or encoded when the video can simply be copied. Tools that re-encode everything spend an hour making a film look slightly worse; this copies it in seconds.
Is my film stored anywhere?
No — which matters most here, because films are large. Nothing is sent anywhere, and the output is written to your device's own storage as it goes, not held in memory.
What happens to subtitles and extra languages?
They are left out, and the result says how many tracks were dropped. MKV was designed to hold many tracks and MP4 was not, so if you need the subtitles, keep the MKV and play it in VLC.
My MKV plays with no sound after converting elsewhere.
That is the Dolby Digital problem: the sound was copied into a container whose players cannot decode it. Here that sound is converted to AAC, so you get sound everywhere.
What about HEVC (H.265) files?
They are copied across as HEVC, which modern Apple devices, TVs and recent Windows play. If you need maximum compatibility, choose "Play anywhere" and it is re-encoded to H.264 instead.
Good to know: Only the first video and sound track are kept. Chapters, tags and attached fonts or covers are not carried into the MP4.
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