Is MKV to MP4 lossless?

When the video is H.264, HEVC, AV1, VP9 or VP8 and the audio is AAC, MP3, Opus or FLAC, every stream is copied unchanged, so the MP4 is identical in quality. Only tracks that MP4 cannot hold are re-encoded.

What happens to the subtitles in my MKV?

They are dropped. Subtitle tracks and chapter markers are not carried over to the MP4. If you have the subtitles as a separate .srt file, keep it next to the video with the same name and most players will load it automatically.

My MKV has AC-3, E-AC-3 or DTS audio. Will it work?

Those codecs are not permitted in MP4, so the audio has to be re-encoded to AAC or Opus while the video is still copied. That step relies on your browser being able to decode the original track, which is not guaranteed for Dolby and DTS formats; if the conversion fails, this is the likely cause.

Will the MP4 play on my TV or iPhone?

If the MKV held H.264 and AAC, the MP4 plays almost anywhere. HEVC needs a device with HEVC support, and VP9 or AV1 inside MP4 is handled by browsers, Android and VLC but not by every TV or Apple app.

Why is the MP4 almost the same size?

Because nothing was compressed again. A remux only swaps the wrapper, so the size changes by a few kilobytes of container overhead. To shrink the file, use Compress Video or pick a lower Max resolution here.

Does it work with multi-gigabyte files?

Often, on a desktop or laptop. The input and output are held in RAM, so large files are limited by your device's memory, and a full-length film is unlikely to fit on a phone.

MKV to MP4 Converter — Fast Remux, No Quality Loss

Convert MKV to MP4

Repackage MKV downloads and rips as MP4 so they play on phones, TVs and in editors. Video and audio are copied straight across, so it is fast and nothing is re-encoded.

No upload — runs in your browser

Batch convert & ZIP download

Free, no sign-up

Drop MKV files here

Choose files

Free: up to 5 files per batch · Files never leave your device · Paste from the clipboard works too

Private by design

Your files are processed by your own device using WebAssembly and your browser's built-in codecs. Nothing is uploaded, logged or stored.

Fast & offline-ready

No queue, no waiting for a server. Once the page has loaded it even works without a connection.

Works everywhere

Chrome, Edge, Firefox and Safari on Windows, macOS, Linux, Android and iOS. No app to install.

Where MKV files come from

Matroska, the format behind .mkv, is an open container that can hold practically any video codec, any number of audio tracks, soft subtitles, chapters and attachments in a single file. That flexibility is why it is the default for Blu-ray and DVD rips made with MakeMKV or HandBrake, for OBS recordings (OBS long recommended MKV so that a crash cannot corrupt the file), and for yt-dlp downloads that marry a VP9 video stream to an Opus audio stream. The downside is support: Windows and Android play MKV reasonably well, but iPhones, Apple TV, many smart TVs, PowerPoint, Premiere Pro and most web upload forms want .mp4.

What happens to each track

Inside the MKV	In the MP4
H.264, HEVC, AV1, VP9 or VP8 video	Copied unchanged
AAC, MP3, Opus or FLAC audio	Copied unchanged
AC-3, E-AC-3, DTS or Vorbis audio	Re-encoded to AAC or Opus (needs a browser that can decode it)
Subtitle tracks (SRT, ASS, PGS)	Not carried over
Chapters and attachments	Not carried over

For the typical rip or download that means a pure remux: Tinyvert reads the packets out of the Matroska structure and writes them into MP4 boxes without touching the compressed data. There is no generation loss, no codec licensing question and no waiting for an encoder. A two-hour film takes about as long as reading it from disk.

Subtitles need a plan

Because MP4 output does not receive the subtitle tracks, decide what you need before converting. If the MKV contains soft subtitles you want to keep, extract them with a tool such as MKVToolNix and store the resulting .srt alongside the MP4; VLC, Plex and most players pick it up by matching the file name. Burned-in subtitles are part of the picture and are unaffected.

Copied versus re-encoded

The Quality and Max resolution fields sit under the drop zone but are ignored during a copy. They come into play only when a re-encode happens, either because a stream is not allowed in MP4 or because you ask for a smaller picture. Set Max resolution to 1080p or 720p, for instance, and a 4K rip is decoded, downscaled and encoded with the browser's hardware-accelerated H.264 encoder where available; the row then says "re-encoded". Video is never upscaled.

Private by design

Rips and downloads are personal, and large. Both points favour doing the work locally: nothing is uploaded, nothing waits in a queue on a server, and the only constraint is the memory of the device you use. The page works offline after its first load in Chrome, Edge, Brave, Opera, Safari 17 or newer or Firefox 130 or newer. WebM files follow the same path with WebM to MP4, any other container goes through the Video Converter, and Video to MP3 pulls just the soundtrack out of an MKV.

How to convert mkv to mp4 — step by step

Drop up to five MKV files on the page or click "Choose files". They start converting immediately, one after another, each with its own progress bar.
Keep Quality and Max resolution on their defaults for a straight copy; change them only if you want the video downscaled and re-encoded.
Each finished row shows the new size and whether the streams were "copied" or "re-encoded". Download them individually or all together as a ZIP.

Frequently asked questions

Is MKV to MP4 lossless?: When the video is H.264, HEVC, AV1, VP9 or VP8 and the audio is AAC, MP3, Opus or FLAC, every stream is copied unchanged, so the MP4 is identical in quality. Only tracks that MP4 cannot hold are re-encoded.
What happens to the subtitles in my MKV?: They are dropped. Subtitle tracks and chapter markers are not carried over to the MP4. If you have the subtitles as a separate .srt file, keep it next to the video with the same name and most players will load it automatically.
My MKV has AC-3, E-AC-3 or DTS audio. Will it work?: Those codecs are not permitted in MP4, so the audio has to be re-encoded to AAC or Opus while the video is still copied. That step relies on your browser being able to decode the original track, which is not guaranteed for Dolby and DTS formats; if the conversion fails, this is the likely cause.
Will the MP4 play on my TV or iPhone?: If the MKV held H.264 and AAC, the MP4 plays almost anywhere. HEVC needs a device with HEVC support, and VP9 or AV1 inside MP4 is handled by browsers, Android and VLC but not by every TV or Apple app.
Why is the MP4 almost the same size?: Because nothing was compressed again. A remux only swaps the wrapper, so the size changes by a few kilobytes of container overhead. To shrink the file, use Compress Video or pick a lower Max resolution here.
Does it work with multi-gigabyte files?: Often, on a desktop or laptop. The input and output are held in RAM, so large files are limited by your device's memory, and a full-length film is unlikely to fit on a phone.

Convert MKV to MP4

Private by design

Fast & offline-ready

Works everywhere

Where MKV files come from

What happens to each track

Subtitles need a plan

Copied versus re-encoded

Private by design

How to convert mkv to mp4 — step by step

Frequently asked questions

Further reading

Related tools