M4A → OGG
M4A to OGG converter
The AAC or Apple Lossless audio inside the M4A is decoded and encoded to Ogg Vorbis. From AAC that is a lossy-to-lossy transcode; from Apple Lossless it is a single, clean Vorbis encode.
…or drag files and folders here. Add as many as you like — everything is processed on this device.
.aac .caf .m4a .m4r .m4v .mp4
In one paragraph
M4A is the format Apple devices hand you, and Ogg Vorbis is the one a surprising number of open tools insist on. Godot imports Ogg Vorbis, WAV and MP3 but not AAC. Wikimedia Commons accepts Ogg and FLAC but rejects M4A uploads outright. Some Linux distributions ship without an AAC decoder, so an M4A from a phone simply will not play until it is converted.
Sonic Batch reads the MP4 container, decodes whichever codec is inside — usually AAC, sometimes Apple Lossless (ALAC) — and encodes Vorbis with libvorbis in a WebAssembly build of FFmpeg. Each queue row names the detected codec once the engine has read the file, and only AAC sources are flagged as a second lossy generation.
Does this change the audio quality?
From an AAC M4A this is a second lossy generation: Vorbis has to encode AAC’s artefacts as well as the music, so give it a quality setting above what the source bitrate suggests. From an Apple Lossless M4A there is only one lossy step, the Vorbis encode itself.
- iTunes Store purchases protected with FairPlay DRM cannot be decoded by any local tool and are reported as unsupported.
- Apple’s players have long lacked Ogg Vorbis support, and many iPhones and Safari versions in use still cannot play it. If the file has to play on Apple devices, keep the M4A.
- Vorbis comments carry title, artist, album and track number across, but cover art is not written into the Ogg file.
A worked example
Using phone recordings as sound effects in a Godot project
- Drop the .m4a recordings into the queue and check the codec column — AAC for most phone audio.
- Leave rate control on Quality 6, which gives Vorbis enough room to avoid stacking audible artefacts on the AAC.
- Set Channels to Mono for effects the engine will position in space; it halves the file again.
- Convert all, download the ZIP and drop the .ogg files into the project’s res:// folder.
Quality 6 for AAC sources, 5 for Apple Lossless
A typical 256 kbps AAC M4A sounds transparent to most people, and the job here is to keep it that way. Vorbis quality 6, around 192 kbps, leaves enough headroom that the second encode is very hard to hear. If the M4A is Apple Lossless, quality 5 is already a clean first-generation encode. Dropping to 3 or 4 is fine for speech and effects where file size matters more than detail.
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 |
|---|---|---|---|---|---|
| M4A | Apple’s default AAC container. Better quality than MP3 at the same bitrate. | Native | Native | Native | Native |
| M4R | An M4A file with a .m4r extension. iOS only lists it as a ringtone if it is ≤ 40 seconds. | Partial | Partial | Native | Native |
| MP4 | The standard video container. Its audio track is almost always AAC. | Native | Partial | Native | Native |
| AAC | Bare AAC frames with no MP4 wrapper — used by broadcast streams and some hardware. | Native | Partial | Native | Native |
| CAF | Apple container used by older iOS Voice Memos. Usually holds ALAC, IMA4 or raw PCM. | Engine | Engine | Partial | Partial |
| Output | Encoder | Bitrates / depth | Sample rates | Tags |
|---|---|---|---|---|
| OGG | libvorbis | 32–320 kbps | 8–96 kHz | Yes |
- 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 file is rejected as DRM protected.
Older iTunes Store purchases (.m4p) and some Apple Music downloads are encrypted. Only unprotected M4A files — your own recordings, GarageBand exports, iTunes Plus purchases and rips — can be decoded.
The Ogg plays everywhere except my iPhone.
Older iOS and Safari versions have no Vorbis decoder. The file is fine; it is a platform gap. Keep the original M4A for Apple devices.
The Ogg file is larger than the M4A.
A high Vorbis quality on a low-bitrate AAC source spends bits re-describing the AAC. Drop to quality 4 or 5 for sources around 128 kbps; going higher cannot add back what the AAC encoder removed.
Frequently asked questions
Is M4A to OGG lossless?
No. Vorbis is a lossy codec, so the encode discards some information. From an AAC source the loss is stacked on top of AAC’s; from Apple Lossless it is a single generation.
Should I choose Opus instead of Vorbis?
Opus is more efficient and is the better pick for voice and streaming where the player supports it. Godot, many game engines and older tools specifically expect Vorbis in .ogg, which is what this page writes.
Can I convert a folder of voice memos at once?
Yes. Choose the folder or drag several files in, apply one setting to all of them and download the results individually or as one ZIP with a manifest.
Is my audio uploaded?
No. Decoding and encoding run as WebAssembly inside your browser tab, served from this site. The application has no upload endpoint.