MKV to MP4 Converter
Upload Video
Drag & drop or click to select a video file
- Upload an MKV file.
- Pick the audio tracks you want to keep (multilingual files).
- Optionally trim the time range.
- Click Convert and wait for completion.
- Download the MP4 file.
Watch the audio tracks when going MKV to MP4
MKV is a Swiss-army container that often holds multiple audio tracks (languages/commentary) and subtitles; MP4 is simpler but plays everywhere. Use the track selector to keep what you need.
Virtually unlimited tracks and subtitles; great for multi-language archives.
Universal playback, but keeps only the first audio track by default (this tool supports multi-select).
For multilingual MKV, pick the language tracks you want before converting.
Help
FAQ
Will it keep the original quality?ShowHide
What happens to my subtitles?ShowHide
Why did my multi-language audio lose tracks?ShowHide
Why does the same MKV sometimes remux instantly and sometimes transcode?ShowHide
Is my file uploaded?ShowHide
How to convert MKV to MP4
- Upload an MKV file.
- Pick the audio tracks you want to keep (multilingual files).
- Optionally trim the time range.
- Click Convert and wait for completion.
- Download the MP4 file.
Privacy
Full guide
MKV to MP4 Converter
Convert MKV/Matroska videos to MP4 for better compatibility on all devices. This is one of the few conversions that is often lossless: since most MKV files already contain H.264 video, changing to MP4 can be a pure container swap with no re-encoding. The complications are all about tracks - subtitles, extra audio languages, and chapters - which this page explains in detail.
What MKV is: the archive-grade container
Matroska (MKV) is an open-source container designed with one goal: hold anything. Unlike MP4, which is a locked-down ISO standard, MKV's specification deliberately imposes almost no limits:
- Unlimited streams. A typical movie MKV carries the video track, 2-8 audio tracks (dub languages, director commentary), multiple subtitle tracks (ASS/SSA styled subtitles, SRT, PGS image subtitles), attachments (fonts, cover art), and chapter markers.
- Codec-agnostic. H.264, H.265, VP9, FLAC, Opus, TrueHD - MKV wraps them all. Whether the player can decode them is a separate question, which is exactly why MKV files sometimes play fine in VLC but not on a TV.
- Error-resilient. Streaming-oriented structure with recovery points, which is why partially downloaded MKV files remain playable.
This flexibility made MKV the de facto standard for HD archiving and multilingual film collections. But the same openness is the source of every MKV→MP4 problem: MP4 is strict, and strictness is precisely why it plays everywhere.
The good case: remux (fast and lossless)
MP4's native codec set is small: H.264/H.265 video, AAC/AC3 audio, mov_text subtitles. If your MKV contains H.264 video + AAC audio - the most common combination for web-downloaded and self-ripped files - then the compressed streams can be stream-copied into MP4:
- No decoding or re-encoding happens
- No quality loss, byte-for-byte identical video data
- Speed limited only by disk I/O, effectively instant
- File size stays the same (usually a tiny bit smaller, since Matroska overhead is slightly higher)
This tool attempts the copy path first for every MKV and falls back to transcoding only when the copy fails - so for well-behaved files you get the best possible outcome automatically.
The three things that don't survive: subtitles, extra audio, chapters
1. Subtitles are usually dropped. MKV subtitles are commonly ASS/SSA (styled, animated - the anime community's format), SRT (plain text), or PGS (bitmap images from Blu-rays). MP4 supports only mov_text, a plain-text codec that ASS styling and PGS bitmaps cannot be copied into. This conversion therefore drops subtitle tracks (-sn), and the honest answer for subtitle preservation is: keep the MKV, or extract the subtitle file separately and load it alongside the MP4 in your player.
2. Extra audio tracks need explicit selection. A default conversion maps only the first audio stream - your Japanese/English/German multi-track movie comes out with exactly one language. This tool probes the file and shows every audio track (index, language, codec, channels) before converting; select all the tracks you want to keep. MP4 handles multiple AAC tracks fine - it's the selection, not the container, that's the usual failure point.
3. Chapter markers are lost. MP4 technically supports chapters, but almost nothing reads them. If you rely on chapters for navigation, that metadata won't make it through.
When MKV → MP4 falls back to transcoding
The remux path fails when the MKV contains codecs MP4 players won't accept:
| Inside your MKV | Remux outcome |
|---|---|
| H.264/H.265 + AAC/AC3 | ✅ Lossless copy - the common case |
| VP9 or Theora video | ❌ Re-encode to H.264 |
| FLAC / Opus / TrueHD audio | ❌ Audio re-encode to AAC (video may still copy) |
| H.265/HEVC video | ⚠️ Copies fine, but older devices can't decode it - that's an MP4 problem, not a conversion problem |
When remux fails, the tool transcodes to H.264 (libx264) + AAC automatically. Quality loss at default settings is visually negligible, but file size can change in either direction depending on how efficiently the original was encoded.
Tips
- MKV to MP4 often works via fast remux (no quality loss)
- If remux fails, transcoding is used automatically
- For multilingual files, check the audio track selector before converting
- Subtitles won't transfer - extract them separately if you need them
- Large MKV files may take longer to process in browser (near-2GB files hit the wasm memory limit)