Free converter · Remux (container swap)
Convert M4V to MKV
Short answer
Drop your M4V file into the converter below and download the MKV file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The video and audio streams are copied into the MKV container without re-encoding, so quality and file size stay the same. If a stream cannot go into MKV (PCM audio cannot go into MP4, for example), the converter re-encodes to H.264 video and AAC audio in Matroska instead.
Maximum file size: 100 MB. The first conversion loads a ~30 MB converter engine, once per visit. Nothing is uploaded - conversion runs on your device.
Streams are copied into Matroska; copy-protected iTunes files cannot be converted. · Remux (container swap) · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The streams were copied: the video and audio checksums were identical before and after, and the 8.88 MB file became 8.88 MB (-0.1%).
- The result holds: Video: h264 1920x1080; Audio: aac 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 0.09 seconds on the single-thread engine; natively, the 10 second clip took 0.11 seconds.
- Next to it: M4V to AAC (-98.2%), M4V to AVI (-70.6%), M4V to GIF (+592%).
Measured: M4V to MKV
The converter's own ffmpeg arguments, run on a 10 second 1920 × 1080 excerpt of Big Buck Bunny (an animated film, not camera footage) saved in M4V. The browser column is the same arguments on the single-thread WebAssembly core with a 3 second excerpt, in a headless run; your device will differ. Results describe this clip and these encoders.
| Check | Result |
|---|---|
| Mode | Streams copied (no re-encoding) |
| Input | M4V, 8.88 MB |
| Output | MKV, 8.88 MB (-0.1%) |
| Output streams | Video: h264 1920x1080; Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 0.11 s |
| Time, browser engine, 3 s clip | 0.09 s |
| Video checksum | Identical |
| Audio checksum | Identical |
Because nothing is decoded, a copy takes a fraction of a second whatever the length of the video.
M4V vs MKV
| M4V | MKV | |
|---|---|---|
| Full name | Apple MPEG-4 video | Matroska |
| What is inside | H.264 video with AAC audio, the same structure as MP4 | Almost any codec, plus several audio and subtitle tracks |
| Compression | Depends on the codec inside | Depends on the codec inside |
| Best for | Apple TV and iTunes; files bought from iTunes may be copy-protected and cannot be converted | Archiving and playback in desktop players; most social platforms do not list it |
What you get
The same streams in an MKV file. When a stream cannot be copied, the converter writes H.264 video and AAC audio in Matroska.
Where you can upload MKV
| Platform | MKV | What the platform documents |
|---|---|---|
| YouTube Shorts | Unclear | MKV is absent from YouTube's published upload-format list. |
| TikTok | Not accepted | MKV is not listed for TikTok Content Posting API uploads. |
| Instagram Reels | Not documented | MKV is not in Instagram's published video specs, which list MOV and MP4. Convert to MP4 before uploading. |
Planning a bigger file
These are estimates scaled up from the 10 second clip. Real files differ with content, resolution and bitrate, so treat them as an order of magnitude, not a promise.
| Length of the video or recording | Input size (like ours) | MKV size | Time in your browser |
|---|---|---|---|
| 1 minute | 53.18 MB | 53.14 MB | 2 seconds |
| 10 minutes | 531.79 MB | 531.44 MB | 18 seconds |
| 1 hour | 3190.73 MB | 3188.63 MB | 1.8 minutes |
An M4V file of this kind reaches the 100 MB limit of the converter after about 2.0 minutes; converting it would take roughly 4 seconds on the single-thread engine, and the MKV would be about 104.79 MB.
M4V and MKV next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| M4V to MKV | Copy | -0.1% | 0.11 s |
| M4V to AAC | Re-encode | -98.2% | 0.30 s |
| M4V to AVI | Re-encode | -70.6% | 1.5 s |
| M4V to GIF | Re-encode | +592% | 5.5 s |
| M4V to M4A | Re-encode | -98.2% | 0.30 s |
| M4V to MOV | Copy | 0.0% | 0.09 s |
| M4V to MP3 | Re-encode | -98.2% | 0.24 s |
Choosing MKV
MKV: Matroska. Archiving and playback in desktop players; most social platforms do not list it. M4V: Apple MPEG-4 video. Apple TV and iTunes; files bought from iTunes may be copy-protected and cannot be converted.
- Use this conversion when a program wants the other container; the picture and sound stay exactly as they were.
- If the destination states the format it accepts, use that and nothing else.
Questions people ask
Is this M4V to MKV converter free and private?
Yes. It is free, needs no account and runs entirely in your browser, so the file never leaves your device.
Will converting M4V to MKV reduce quality?
Not when the streams fit MKV: they are copied unchanged. Only if a stream has to be re-encoded is there a small, usually invisible loss.
Is there a file size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit; larger files are better handled by a desktop app such as HandBrake or FFmpeg.
How do I convert M4V to MKV?
Choose the file in the converter above and download the MKV. It runs in your browser with no upload.
Will converting M4V to MKV reduce quality?
No. The streams are copied, and in our test the checksums were identical.
Why did the file size change by -0.1%?
A copy only changes the container, so the size stays about the same.
How long does it take?
A 3 second clip took 0.09 seconds in the browser engine in our test; time grows with the length of the file.
How long will an M4V file of 100 MB take?
At the speed we measured in the browser engine, about 4 seconds for a file like our clip. Your device and the content will change it.
Is my file uploaded?
No. The conversion runs in your browser.
Is there a size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit.
More converters
Sources and how we checked
- MDN: Media container formats
- MDN: Web audio codec guide
- MDN: Image file type and format guide
- FFmpeg documentation: stream copy
- FFmpeg Documentation: ffmpeg (stream selection, -map, -c copy) (read 2026-10-09)
- MDN: Media container formats (read 2026-10-09)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-09)
Reviewed October 8, 2026. What the converter writes was measured with ffprobe on the same FFmpeg build your browser downloads; format descriptions follow MDN's media guides.