iPhone Voice Memo → MP3
iPhone voice memo to MP3
Voice Memos records AAC in an .m4a container on modern iOS and CAF on older versions. Both are decoded locally and re-encoded to MP3, tuned for speech.
…or drag files and folders here. Add as many as you like — everything is processed on this device.
.aac .caf .m4a .m4v .mov .mp4 .qt
In one paragraph
Voice Memos is the recorder most people actually use — for interviews, lectures, song ideas, meeting notes and rehearsal takes. What it produces is an .m4a file (or a .caf on iOS 11 and earlier), and the moment you need to hand that to a transcription service, a Windows-based colleague, an editor or a court, MP3 is what is asked for.
This page is tuned for that job specifically: mono output, a speech-appropriate bitrate, and loudness normalisation to −16 LUFS so a memo recorded in your pocket and one recorded on a desk end up at the same level. It runs on the iPhone too — pick the memos through Safari’s Files picker.
Does this change the audio quality?
Voice Memos records AAC at roughly 32 kbps mono in Compressed mode and lossless in Lossless mode. Converting Compressed recordings to MP3 is a second lossy generation, which is why a slightly higher MP3 bitrate is worth it.
- Recordings made in Lossless mode are large — a one-hour memo can exceed the 400 MB per-file budget. Export it as Compressed from the Voice Memos app first.
- Trimming and enhancement done inside the Voice Memos app is baked into the exported file; this tool sees only what was exported.
- On iPhone the engine runs single-threaded and one file at a time. A 30-minute memo is comfortable; a four-hour one is not.
A worked example
A one-hour interview that needs transcribing
- In Voice Memos, share the recording to Files (or AirDrop it to a computer).
- Open this page, pick the file, and leave the Podcast/voice preset with normalisation on.
- Optionally turn on silence removal with a −45 dB threshold to cut the two minutes of room tone before the interview started.
- Download the MP3. The panel shows the measured input loudness and the exact gain that was applied.
96 kbps mono, normalised to −16 LUFS
That is about 0.7 MB per minute — a one-hour interview is roughly 43 MB, comfortably emailable and accepted by every transcription service. Mono is correct because the iPhone records a single microphone; converting to stereo doubles the size and duplicates the same signal. −16 LUFS is the spoken-word convention, and normalising to it means a batch of memos recorded in different places plays back consistently.
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 |
| CAF | Apple container used by older iOS Voice Memos. Usually holds ALAC, IMA4 or raw PCM. | Engine | Engine | Partial | Partial |
| MOV | QuickTime video from iPhone and DSLR cameras. Audio is normally AAC or PCM. | Partial | Engine | 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 |
| Output | Encoder | Bitrates / depth | Sample rates | Tags |
|---|---|---|---|---|
| MP3 | libmp3lame | 32–320 kbps | 8–48 kHz | Yes + artwork |
- 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
Safari on my iPhone will not let me pick the recording.
Share the memo to the Files app first (Share → Save to Files). Safari’s file picker reads from Files and iCloud Drive, not directly from the Voice Memos database.
The tab reloaded partway through a long recording.
iOS reclaims memory from background tabs aggressively. Keep the tab in the foreground, convert one file at a time, and export the memo as Compressed rather than Lossless.
The output is much quieter or louder than I expected.
Normalisation targets −16 LUFS, which is quieter than a mastered music track by design. Turn normalisation off if you want the original level preserved exactly.
Frequently asked questions
Where are my recordings sent?
Nowhere. The file is read from your device into the browser tab and processed there. This is the main reason to use a local tool for interviews and meetings: no third party ever holds the recording.
Can I do this entirely on the iPhone?
Yes. Safari on iOS runs the single-threaded engine. It is slower than a desktop and handles one file at a time, but it works without any app install.
Why not just rename the .m4a to .mp3?
Because the contents are AAC, not MP3. Renaming produces a file that most software rejects. A real decode-and-encode is required.
Should I remove silence?
It is useful for trimming the dead air at the start and end of a recording. Leave interior silence alone for interviews — cutting pauses out of speech makes transcription timestamps meaningless.