Convert MKV to MP4 online
Convert an MKV file you already have on your device into an MP4 that plays on any player, without re-encoding the video or uploading it to any server.
Convert MKV to MP4
Your file is processed right in this browser: it never gets uploaded to any server.
Why use PullVid for MKV → MP4?
Conversion details
How do you convert an MKV to MP4?
Choose the MKV file you want to convert to MP4.
Hit 'Convert'; since it's a remux (no re-encoding), it usually takes only a few seconds.
Download the resulting MP4; it saves straight to your device.
If you already have a video saved in MKV format and need to play or share it on a device that doesn't handle it well, this converter turns it into MP4 without touching or re-encoding the video. Everything happens in your own browser: we never upload the file to a server.
What's converting an MKV to MP4 good for?
MKV is the go-to container for movie and TV rips because it can hold multiple audio tracks, subtitles and high-quality codecs in a single file. The catch is that many phones, smart TVs, editing programs and social networks either play it poorly or reject it outright. MP4, on the other hand, plays pretty much everywhere. Converting the container without touching the video fixes that compatibility problem in seconds.
How it works: instant remux, not re-encoding
We use ffmpeg compiled to WebAssembly with direct stream copy ('-c copy'): instead of decompressing and recompressing the video (which would take minutes and lose some quality), we simply repackage the same video and audio data inside an MP4 container. That's why the conversion is nearly instant, even with files several GB in size, and the result is identical in quality to the original.
Steps to convert your MKV to MP4
- Choose the MKV file from your device ('Choose file' button).
- Hit 'Convert'. The first time, your browser downloads the conversion engine (a few MB); after that, it's faster.
- Wait a few seconds for the remux to finish.
- Download the resulting MP4 with the 'Download result' button.
What carries over and what doesn't: subtitles and uncommon tracks
The main video and audio copy over with zero loss. What does not make it into the MP4 are subtitles embedded in ASS/SSA format (the typical fansub style, with custom colors and positioning) because MP4 doesn't support them; nor do less common audio codecs like DTS-HD or TrueHD, common in Blu-ray rips. If your MKV uses standard video and audio (H.264/H.265 + AAC or AC3), the remux works without any issues.
Honest limits worth knowing
Since the process runs in your browser, the real limit is your device's memory when loading the file, not an artificial cap of ours. With very large files (several GB), loading can take longer, especially on phones with limited RAM — try a computer if that happens. If the remux fails, it's almost always because the MKV carries a codec MP4 doesn't support (see above), not a size limit.
Other related conversions
If your video comes in another container, you can also convert a MOV to MP4 (just as fast, same remux) or a WebM to MP4 (this one does require re-encoding). If all you want is the audio, try MP4 to MP3 once you have the file in MP4. If you don't have the video yet, use our YouTube video downloader.
Frequently asked questions about MKV → MP4
Why is converting MKV to MP4 so fast?
Because it's a remux: we don't re-encode the video or the audio, we just swap the container that wraps them. It's basically copying the same data into an MP4 file, so it takes seconds even with videos several GB in size.
Do I lose quality converting an MKV to MP4?
No. By copying the video and audio streams without re-encoding (ffmpeg's '-c copy' option), the result is exactly the same quality as the original MKV, bit for bit.
Do subtitles and all audio tracks carry over?
The remux copies the main video and audio track, but the MP4 container doesn't support subtitles embedded in ASS/SSA format (very common in MKV), so if the file has them, they won't be included in the result. It also doesn't support some less common audio codecs, like DTS or TrueHD, without re-encoding.
Why does the conversion sometimes fail?
MP4 doesn't support every codec an MKV can carry (DTS or TrueHD audio, or very old video codecs, for example). If the file uses one of those, the remux fails because MP4 can't wrap them without re-encoding; in that case you'd need a desktop program that can actually re-encode those tracks.
Is there a size limit on the MKV file?
We don't set an artificial limit, but the process runs in your browser: files above 2 GB can use a lot of memory just to load, especially on phones with limited RAM. The remux itself is fast; loading the file is usually the bottleneck, not converting it.
I don't have the MKV file yet — can I download it here?
This converter works with an MKV file you already have saved, from a download manager or a recording, say. Our YouTube video downloader delivers directly in MP4, so you usually won't need to convert anything after downloading with PullVid.