What happens when you convert M4A to MKV
- MKV is a video format. The audio is encoded as AAC audio, and by default the file has no picture.
- Tick "Add a black video track" if the MKV is going to YouTube or another site that rejects audio-only video.
How to convert M4A to MKV online
- Press "Choose M4A files" and select one or more files, or drag them onto the box. You can add files of any size your device can hold in memory.
- Adjust the settings if you need to: resolution and quality control the size of the result. The defaults suit most people.
- Press "Convert to MKV". The first audio or video conversion downloads the converter engine, about 32 MB, which your browser then keeps for next time.
- Save each MKV with its download button. Close the tab and every trace of the files is gone from memory.
Why convert M4A to MKV?
M4A files usually come from iTunes purchases, iPhone voice memos and Apple Music downloads. People convert them to MKV because MKV keeps several audio and subtitle tracks in one file and is the favourite container of media servers such as Plex and Jellyfin.
In short, M4A is good at what it was made for, and MKV is the more practical choice when the file has to play, upload or edit somewhere else. M4A plays in all current browsers and every Apple device, while Chrome and Edge play many MKV files; Safari and iPhones do not.
How to convert M4A to MKV on Windows, Mac, iPhone and Android
On Windows
Open this page in Chrome, Edge or Firefox, drag your M4A files in from File Explorer, and press Convert. Each MKV is saved to your Downloads folder. If you prefer a desktop program, VLC can also convert M4A to MKV: choose Media, then Convert / Save.
On a Mac
Safari, Chrome and Firefox all work. Drag the M4A files from Finder onto the drop zone and the MKV files land in Downloads.
On iPhone and iPad
Open the page in Safari and tap Choose M4A files. You can pick from Photos or from the Files app. The converted MKV appears in Files, in the Downloads folder; to put it in your photo library, open it there, tap Share and choose Save Video.
On Android
Open the page in Chrome, tap Choose M4A files and pick them from Files or your gallery. The MKV is saved to the Download folder, where any file manager can find it. Keep the screen on while a long video converts, because Android may pause a tab in the background.
Best settings for M4A to MKV
Leave Resolution on Keep original and Quality on Standard if the video only needs to change container: that is what lets the tool copy the H.264 stream straight into the MKV, which is fast and loses nothing.
If the file is too big, change either setting and the video is re-encoded with H.264. Quality uses the CRF scale: High is 20, Standard 23 and Smaller file 28. As a rule of thumb each step of about 6 on that scale halves or doubles the size. Dropping from 1080p to 720p usually saves more than lowering the quality, and it also makes the conversion much faster.
M4A vs MKV: the differences
| M4A | MKV | |
|---|---|---|
| Full name | MPEG-4 Audio | Matroska video |
| Type | audio | video |
| Created by | Apple, on the MPEG-4 standard | the Matroska project |
| First released | 2001 | 2002 |
| Compression | Lossy or lossless | Lossy |
| Usually contains | AAC, or ALAC for lossless files | almost any codec, often H.264 or H.265 with several audio and subtitle tracks |
| In a browser | plays in all current browsers and every Apple device | Chrome and Edge play many MKV files; Safari and iPhones do not |
| Common uses | iTunes purchases, iPhone voice memos and Apple Music downloads | films and TV rips, OBS recordings and anime releases |
| MIME type | audio/mp4 | video/x-matroska |
About M4A and MKV files
What is an M4A file?
M4A is an MP4 file that only holds audio, which is why renaming one to .mp4 often works. Voice Memos on iPhone saves recordings as M4A.
What is an MKV file?
MKV can hold unlimited audio tracks, subtitle tracks and chapters in one file, which is why film rips use it. OBS offers MKV recording because a crash part way through does not corrupt the whole file.
M4A to MKV not working? Common problems
- The conversion is slow. Audio and container changes take seconds, but re-encoding video runs on your own processor. Lower the resolution to 720p, close other tabs, and keep the device plugged in.
- The tab stops or reloads on a very large file. Browsers limit how much memory one tab can use, around 2 GB and less on phones. Split long recordings or convert them on a computer.
- The MKV will not play on an old device. Try the other formats offered for M4A, or choose 720p, which older players handle more reliably.
Convert M4A to MKV with ffmpeg
This converter runs ffmpeg inside your browser. If you would rather use the ffmpeg command line on your own computer, this command produces an equivalent MKV with the same kind of settings:
ffmpeg -i input.m4a -c:v libx264 -crf 23 -c:a aac -b:a 128k output.mkvReplace input.m4a with the name of your file. For a whole folder of M4A files, run the command in a loop, or drop them all on the converter above, which processes them one after another.
M4A to MKV converter FAQ
Will I lose quality converting M4A to MKV?
A little. Both formats are lossy, so re-encoding compounds the loss slightly. Keep the default quality or higher and the difference is rarely noticeable.
Why is the MKV a different size from the M4A?
Without a picture, the MKV is about the size of the audio. Adding a black video track adds a little, because a still black frame compresses to almost nothing.
Are my M4A files uploaded anywhere?
No. The conversion runs inside this browser tab using ffmpeg compiled to WebAssembly, so your files stay on your device. You can disconnect from the internet after the page and converter engine have loaded and it still works.
Can I convert several M4A files to MKV at once?
Yes. Select or drop as many files as you like; they are converted one after another and each gets its own download button.
How do I open an MKV file?
Chrome and Edge play many MKV files; Safari and iPhones do not. MKV is common for films and TV rips, OBS recordings and anime releases.
Is this M4A to MKV converter free?
Yes. There is no sign-up, no watermark and no limit on how many files you convert. The site is paid for by advertising, and because conversions run on your device there is no server cost per file.
Can I convert M4A to MKV on my phone?
Yes. The converter works in Safari on iPhone and iPad and in Chrome on Android. Long HD videos convert more slowly on a phone than on a computer.