Free MP4 to MKV converter in your browser: no upload, no re-encoding. Tested with real MP4 files above 20 GB on desktop Chrome and Edge.
Price Currency: USD
Operating System: Web Browser
Application Category: MultimediaApplication
VidCon Free MP4 to MKV Video Converter
VidCon is a free MP4 to MKV converter that runs in your browser: no upload, no signup, no re-encoding, so the quality stays identical. It has no built-in size limit — your free disk space is the only cap (tested with real MP4 files above 20 GB on desktop Chrome or Edge).
- FreeNo watermark, no file size cap
- PrivateYour videos stay on your device
- LosslessNo re-encoding, no quality loss
- InstantNo upload, no download, no wait
Change the container. Keep every bit of quality.
As an MP4 to MKV converter, VidCon rewrites a video’s container — the wrapper that holds the picture and sound — without decoding or re-encoding what is inside. The video and audio streams are copied across byte for byte, so the result is not “almost as good” as the original. It is the original, in a different box. Before starting, VidCon reads the track list of your file and checks that the video and audio can be copied across. If the picture or the sound cannot be copied, the job stops and says so rather than re-compressing it. Anything this page does not carry — a subtitle track, chapters, attached files — is named in the result, never dropped without a word.
Remuxing, Not Re-encoding
Most online video converters decode your video and compress it again. That is why they are slow, why they cap your file size, and why the result is always slightly worse than what you started with. Every re-encode is a generation of loss you cannot get back.
This MP4 to MKV converter does something different and much cheaper: it remuxes. A video file has two parts — the compressed streams, and the container that indexes them. An MP4 and an MKV holding the same H.264 video and AAC audio contain identical media; they simply describe it differently. Remuxing unwraps the streams from one container and rewraps them in another, touching the compressed data only to copy it.
The consequences are worth stating plainly, because they are what makes this MP4 to MKV converter unusual:
- Quality is mathematically unchanged. Not “visually lossless” — literally the same bytes.
- Speed is limited by your disk, not your processor. There is nothing to compute.
- Memory use stays flat regardless of file size, because the file streams through in small pieces.
How to Convert a Video, Step by Step
Using this MP4 to MKV converter takes three steps and no account. Use desktop Chrome or Edge if your file is large.
- Add your files. Drag them onto the drop area, or click Choose files. On desktop you can queue up to 20; they convert one at a time so memory and disk pressure stay low. On mobile, one file at a time.
- Choose a save folder. Click Choose Save Folder and approve write access once. This is what lets VidCon stream the new file straight to disk instead of building it in memory — it is the reason there is no size limit. Tick Remember and the same folder is reused next time.
- Click Convert All. Progress shows per file and overall. VidCon first reads the track list of your source and confirms the video and audio can be copied into MKV without re-encoding. When a file finishes, VidCon reopens it and checks the track list and duration before marking it done, so “Done” always means verified.
Reading the result. Each finished item shows the output size and how many tracks were carried across. If your file also held something this page does not carry, such as a subtitle track, the same line says “left out” and names it. If a file fails, the queue shows the reason in plain language — for example that an H.264 video track cannot be copied into WebM — rather than a generic error.
The Memory Problem Everyone Else Hits
Browser-based converters usually fail on large files for one specific reason: they load the file into memory. Most are built on a WebAssembly build of FFmpeg, which uses a 32-bit memory model with a hard ceiling near 2 GB per instance. A 20 GB video cannot fit, so these tools either refuse large files outright, or split the work into passes and reassemble the pieces afterwards — which is where corruption and missing sections creep in.
This MP4 to MKV converter never holds the file in memory. It reads the source in small slices, hands each slice to the muxer, and writes the finished bytes straight into the folder you chose. At no point does a complete copy exist anywhere except on your disk. Memory use is therefore roughly constant whether the file is 200 MB or many gigabytes.
| Source file | Environment | Peak memory | Result |
|---|---|---|---|
| 25.15 GB MP4 (H.264 + AAC) | Microsoft Edge | 179 MB | Completed (output not saved) |
| 25.15 GB MP4 (H.264 + AAC) | Google Chrome | 114 MB | Completed (output not saved) |
| 23.90 GB MP4 (H.264 + AAC) | Controlled engine test | 285 MB peak RSS | Duration matched to 0.00035 s |
These are measured runs, not a ceiling. Your practical limit is free disk space: you need room for the new file alongside the original.
This Is a Disk Job, Not a Processor Job
Because this MP4 to MKV converter recompresses nothing, your processor is barely involved. The work is reading bytes and writing bytes. That means the single biggest factor in how long a conversion takes is your storage speed — and it means a modest laptop performs close to a high-end desktop on the same file.
| Storage path | Same 16.62 GB source | Bound by |
|---|---|---|
| Hard drive to hard drive | about 8 min 2 s | disk speed |
| NVMe SSD to NVMe SSD | about 3 min 5 s | disk speed |
To get the best time, keep the source and the destination on the same fast drive, close other heavy applications, and leave the tab open while it runs. Your exact time will vary with file size, bitrate, drive condition, free space and background activity such as antivirus scanning.
Nowhere. That Is the Whole Point.
When you use a cloud MP4 to MKV converter, your video is uploaded to a server you do not control, processed there, and retained for some period described in a policy you probably did not read. For personal recordings, client work, or anything confidential, that is a meaningful exposure — and for a 20 GB file it is also a very long upload.
VidCon loads its interface and its conversion engine from the web, exactly as any web page loads its code. After that, your video is read by the browser directly from your disk and the new file is written directly back to a folder you nominate. The video data never travels to AIToolboxBD or anywhere else. There is no account, no queue, and no copy left on a server, because there is no server in the path.
You can verify this yourself: open your browser’s developer tools, switch to the Network tab, and run a conversion. You will see the page assets load, and then no upload traffic at all.
No Hidden Copies on Your Drive
Some browser tools stage large temporary files in private browser storage. That storage survives closing the tab, is hard to find, and can quietly use a lot of space on your system drive.
This MP4 to MKV converter stages nothing. It writes one file: the output, in the folder you selected. To confirm it, run a few conversions and then check your browser’s storage usage — it should not grow.
Use Chrome or Edge on Desktop for Large Files
Writing a 20 GB file directly into a folder requires the File System Access API, which today is available in Chromium-based desktop browsers — Chrome, Edge, and most Chromium derivatives — on a secure HTTPS page. This is what lets VidCon stream output to disk instead of assembling it in memory, and it is why large files work at all.
Firefox and Safari do not currently implement that API. They can still handle smaller files through the standard download path. Mobile browsers are constrained by device storage and background-tab limits; mobile is supported for a single modest file at a time, but a large conversion belongs on a desktop.
You will be asked once to grant write permission to the folder you pick. That permission covers only the folder you selected — it is not access to your computer, your other files, or your browsing data — and you can revoke it at any time in your browser’s site settings.
How VidCon Compares, With Dates and Sources
VidCon is an MP4 to MKV converter that does one job: it changes the container of a video without re-encoding it. It is not better at everything — if you need to re-encode, resize or edit, a desktop application is the right tool and we say so. The tables use only what each provider states on its own pages. Where a page does not state a figure, the cell says so. In the tables, red marks a limit or a cost for you, amber marks a figure the page does not state, and the colours orange and green are used for VidCon only.
| Tool | Where your video is processed | Free file-size limit | Free daily limit | Account | Kept on their servers | Source |
|---|---|---|---|---|---|---|
| VidCon | In your browserNothing is uploaded | No built-in limitYour free disk space is the only cap. | No daily limit | No account needed | Nothing is storedNothing is uploaded | |
| CloudConvert | Their serversFiles are “temporarily stored” there | 1 GB | 10 a dayConversions; 5 min of processing each | Sign-upShown on the free plan | Up to 24 hoursDeleted at the latest after 24 hours | |
| FreeConvert | OnlineUploaded files are deleted after 8 hours | 1 GB | 20 min a dayOf conversion time; 5 minutes per file | Not neededon the website | 8 hours | |
| Convertio | Online“Runs on our infrastructure” | 1 GB“1 GB maximum file size or Sign Up” | Not stated | Sign-upOffered for more | Not stated | |
| Ezgif | OnlineCopies the streams without re-encoding | 200 MB | Not stated | No account“no registration” | 1 hourDeleted 1 hour after upload | |
| LocalConvertMP4 to MKV is not named on its page | In your browser“Your files never leave your device” | Max 2 GBin its upload area; its own comparison table lists no cap | None listedin its comparison table | No account | Not applicable |
Compared data based on
| Tool | What its own page says | Where it runs | Source |
|---|---|---|---|
| HandBrake | “It’s free!” It describes itself as a video transcoder, for Windows, Mac and Linux. | Install requiredYour computer | |
| MKVToolNix | “A set of tools to create, alter and inspect Matroska files” for Linux, other Unices and Windows; its author says macOS support ends in the second half of 2026. | Install requiredYour computer | |
| FFmpeg | “A complete, cross-platform solution to record, convert and stream audio and video”; its page shows command-line use. | Install requiredYour computer, command line |
Compared data based on
What the tables show
- The free size limits the providers state are 200 MB (Ezgif) and 1 GB (CloudConvert, FreeConvert, Convertio); LocalConvert shows 2 GB in its upload area.
- VidCon and LocalConvert process the video in your browser; the other four process it on their own servers, and three of them state how long they keep it: 1 hour (Ezgif), 8 hours (FreeConvert), up to 24 hours (CloudConvert).
- VidCon has no built-in size limit and no daily limit.
Practical Answers Before You Convert
How large a file can this MP4 to MKV converter handle?
There is no limit built into VidCon. The practical limit is your free disk space. Because the file streams through in small pieces rather than being loaded into memory, RAM is not the constraint. We have tested real MP4 files above 20 GB in both Chrome and Edge, with browser memory staying between 114 MB and 179 MB.
Which free MP4 to MKV converters limit the file size?
On their own pages, checked on 20 October 2026: Ezgif states 200 MB, and CloudConvert, FreeConvert and Convertio each state 1 GB for free use; LocalConvert shows 2 GB in its upload area. VidCon has no built-in size limit — your free disk space is the only cap. Limits change, so the comparison table in this guide links to each source.
Does this MP4 to MKV converter have a daily limit or need an account?
No. VidCon has no daily limit, no account and no watermark. For comparison, CloudConvert states 10 conversions a day on its free plan and FreeConvert states 20 conversion minutes a day; both are checked against their own pages in the table above.
Will an MP4 to MKV converter reduce my video quality?
No. A container remux copies the existing video and audio streams without decoding them, so the picture and sound are bit-for-bit identical to the source. If the video or the audio cannot be copied losslessly into the container you chose, VidCon stops with a clear message rather than silently re-encoding it. Tracks this page does not carry, such as subtitles, are named in the result as left out; they are never dropped silently.
Will subtitles be kept when I convert MP4 to MKV?
Not on this page. VidCon copies the video and audio tracks into the MKV. If your MP4 also holds a subtitle track, the finished line says so, for example “left out: 1 subtitle track”, so you always know what the new file contains. Subtitles burned into the picture are part of the video and are kept; separate subtitle files stay where they are.
Does this MP4 to MKV converter upload my video?
No. VidCon’s page and engine load from the web, but your video is read directly from your disk and the new file is written directly back to the folder you choose. The video itself never reaches any server. You can confirm this in your browser’s Network tab.
Is my original file modified?
Never. VidCon only reads the source. It creates a separate new file and leaves the original untouched, unmoved and unrenamed.
Why is this MP4 to MKV converter fast even on a slow computer?
Because VidCon remuxes, it copies data rather than recompressing it, so the work is bound by drive speed rather than processor speed. An entry-level laptop performs close to a high-end desktop on the same file. In a recorded test on a 16.62 GB file, the same source took about 8 minutes 2 seconds hard-drive-to-hard-drive and about 3 minutes 5 seconds NVMe-to-NVMe.
Which browsers work with this MP4 to MKV converter?
VidCon needs desktop Chrome or Edge for large files, because writing directly into a folder needs the File System Access API. Firefox and Safari do not support it, so VidCon saves each finished file as a download instead, for files up to 2 GB. Mobile is supported for a single modest file at a time.
Why do I have to choose a save folder?
VidCon streams the output to disk as it is produced, so it needs a folder to write into. Without it, the finished file would have to be assembled in memory first — which is exactly the limitation that caps other browser converters at a few gigabytes.
Does VidCon leave files on my computer?
No. VidCon writes only the output file you asked for, in the folder you selected. It does not stage a hidden second copy in browser storage, so repeated conversions cannot quietly fill your system drive.
Can this MP4 to MKV converter process several files at once?
Yes. VidCon queues up to 20 files on desktop and converts them one at a time on purpose — sequential processing keeps memory and disk pressure low, which is what allows very large files to succeed.
Can I use the converted files commercially?
That depends on your original video, not on VidCon. AIToolboxBD never claims any ownership of the files you convert or of the converted files; whatever rights apply to your original video still apply to the new file.
Other AIToolboxBD Tools That Never Upload
Need the soundtrack out of a video instead of a new container? Use CLiPRiP. For audio-to-audio conversion and trimming, use AudioForge. For background on the container formats themselves, see the Matroska project.