MP4 → M4A
MP4 to M4A converter
The audio track is decoded and re-encoded as AAC in an audio-only M4A container, and the video is dropped. Because the source is normally AAC too, this is a second lossy encode, so match the original bitrate.
…or drag files and folders here. Add as many as you like — everything is processed on this device.
.3g2 .3gp .asf .avi .f4v .flv .m4v .mk3d .mka .mkv .mov .mp4 .qt .weba .webm .wmv
In one paragraph
An M4A is an MP4 with only an audio track in it, which is why Apple Music, iTunes, iPhones and most podcast tools treat it as a song or episode rather than a video. Converting an MP4 or MOV to M4A gets you the same AAC sound in a file that shows up in your music library, plays with the screen off, and is a fraction of the size.
Sonic Batch decodes the video’s audio track in your browser and writes a fresh AAC stream at the bitrate you choose, either as M4A (with tags and cover art support) or as a bare .aac stream for hardware that wants one. It re-encodes rather than copying the original stream, so you can also change the sample rate, switch to mono or normalize loudness in the same pass.
Does this change the audio quality?
The AAC in a phone MP4 is re-encoded rather than copied, which costs one generation of quality. Both sides of this conversion are lossy, so the encoder is working from audio that has already been through a codec. The result is one generation further from the original recording. At or above the source bitrate the change is very hard to hear.
- The AAC stream is re-encoded, not copied bit for bit. Use MP4 to WAV or MP4 to FLAC if you need zero further loss.
- Surround audio is kept as surround unless you set Channels to stereo. Some players handle multichannel M4A poorly.
- Raw .aac files cannot hold tags or artwork. Pick M4A if you want the title and cover to show.
A worked example
Adding a recorded talk to Apple Music
- Drop the MP4 or MOV of the talk into the queue.
- Keep M4A at 128 kbps, which matches what most phones record.
- Fill in the title and artist in the tag editor so it is easy to find in your library.
- Convert, download the M4A, and drag it into the Music app or the Files app on your iPhone.
Match the bitrate of the video’s audio
Phones usually record AAC at 96 to 192 kbps; the queue shows the source bitrate once the file has been read. Choose the same or the next step up. Going lower saves space but adds audible loss on music; going much higher only makes the file bigger, because the new encoder cannot recover detail the first one discarded.
Supported formats, limits and browser notes
Sonic Batch decodes with the browser when it can (faster, no engine download) and falls back to the self-hosted WebAssembly engine when it cannot. Every combination below works in every listed browser; the column only tells you which decoder does the work.
| Input | What it is | Chrome | Firefox | Safari | iOS |
|---|---|---|---|---|---|
| MP4 | The standard video container. Its audio track is almost always AAC. | Native | Partial | Native | Native |
| MOV | QuickTime video from iPhone and DSLR cameras. Audio is normally AAC or PCM. | Partial | Engine | Native | Native |
| MKV | Open video container used for films, TV recordings and OBS captures. Audio is often AAC, AC-3, DTS, Opus or FLAC. | Partial | Partial | Engine | Engine |
| WebM | Open container used by browser recorders and YouTube downloads. Audio is Opus or Vorbis. | Native | Native | Partial | Partial |
| AVI | Legacy Windows video container from camcorders, older cameras and DivX/Xvid files. Audio is usually MP3, PCM or AC-3. | Engine | Engine | Engine | Engine |
| WMV | Windows Media video in an ASF container. Audio is almost always WMA (Windows Media Audio). | Engine | Engine | Engine | Engine |
| FLV | Flash-era web video, still produced by some stream recorders. Audio is AAC or MP3. | Engine | Engine | Engine | Engine |
| 3GP | Legacy phone recording container, normally AMR-NB or low-bitrate AAC audio. | Engine | Engine | Partial | Partial |
| Output | Encoder | Bitrates / depth | Sample rates | Tags |
|---|---|---|---|---|
| M4A | aac | 32–320 kbps | 8–48 kHz | Yes + artwork |
| AAC | aac | 32–320 kbps | 8–48 kHz | No |
- Max per file
- 400.0 MB
- Max per queue
- 4.00 GB
- Max duration
- 4:00:00
- Max archive
- 1.50 GB
These are enforced ceilings, checked before any decoding starts, not measured maximums — a file over the limit is rejected rather than allowed to exhaust the tab’s memory. Real-world capacity is lower on older phones, which is why the scheduler runs one file at a time on iOS and Safari.
Where your audio goes
Nowhere. Your file is read from disk into this browser tab with the File API, decoded and encoded by code running in that same tab, and handed back to you as a download. It is never transmitted.
That is a structural property of the application, not a policy promise: there are no API routes, no server actions and no third-party processing services in this project, so there is nothing capable of receiving a file. The page’s Content-Security-Policy also restricts connections to this origin, and the automated test suite includes a browser test that fails if any network request during import, preview, conversion or download carries media bytes.
The trade-off, stated plainly: results live in your tab’s memory until you download them. Closing or reloading the page discards them. There is nothing on a server to recover, because nothing was ever put there.
Troubleshooting
The M4A shows up as a video in my player.
That happens when a file still contains a video track. Files from this page never do; if you renamed an MP4 to .m4a instead, convert it here to get a real audio-only file.
My car stereo will not play the M4A.
Some older head units only read raw AAC or MP3. Switch the output to AAC, or use MP4 to MP3 for the widest compatibility.
Why does it not just copy the audio without re-encoding?
Re-encoding lets every setting on this page apply, including trimming, mono and loudness, and it guarantees a clean, standard M4A however the source was muxed. The cost is one generation, which at a matched bitrate is very hard to hear.
Frequently asked questions
What is the difference between MP4 and M4A?
Both use the same MPEG-4 container. An MP4 normally holds video and audio; an M4A holds only audio, usually AAC. The .m4a extension tells players to treat it as music.
Can I convert MOV to M4A here too?
Yes. MOV, MKV, WebM, AVI and other video files are accepted, and each produces an audio-only M4A.
How do I get AAC instead of M4A?
Change the output format to AAC. You get a raw ADTS stream with the .aac extension, which some hardware and broadcast tools prefer.
Is anything uploaded?
No. The engine runs in your browser, and the page cannot send your video anywhere.