How to Convert Audio to MP3 on iPhone

Most of Grabio’s audio and video tools run entirely on your iPhone using Apple’s own Shortcuts actions, but MP3 is the one exception. There’s no built-in Shortcuts action that encodes audio to MP3, so Grabio hands the job to VERT, a free converter site, instead of pretending it can do something the iPhone itself can’t.

Why Grabio can’t convert to MP3 on-device

Apple’s Shortcuts app has a native action for converting audio to M4A, which is why converting audio to M4A on iPhone happens instantly and privately, right on your phone. MP3 is different: there’s no equivalent Shortcuts action for encoding MP3, so nothing on iPhone can do this conversion without help from an outside tool.

How to convert audio to MP3 on iPhone with Grabio

1. Add Grabio to your iPhone once, it’s a free Apple Shortcut with no App Store download and no sign-up. Add Grabio to your iPhone.
2. Open the Files app, Voice Memos, or wherever your audio file is, and tap the Share icon on the file.
3. Tap Grabio in the share sheet.
4. Choose Audio → MP3 (open VERT) from the Grabio menu.
5. Grabio opens VERT (vert.sh) in Safari. Because iOS won’t let an app auto-upload a file into a website’s picker, tap the upload area on VERT and select your audio file from the file picker that appears.
6. Choose MP3 as the output format on VERT and download the converted file back to your iPhone.

What VERT says about where your file is processed

I read VERT’s project README on 7 Nov 2026 so you do not have to take my word for it. Here is what it states, next to what it means for you.

VERT README says	What it means for this job
It uses WebAssembly to convert files on your device instead of a cloud	An audio file you pick on VERT is described as converted in your browser, not on a remote server
It converts images, audio, documents and video	MP3 output for an audio file is within what it lists
Local video conversion is supported, but some conversion may need server-side processing on the official instance	This exception is about video. If you are converting a video file instead, read the VERT privacy policy first

That is VERT’s own description of itself, not something I have audited, so for how it handles files in practice check its privacy policy.

Is it private and free on iPhone?

Grabio itself is free with no account and no login. The MP3 step happens in VERT rather than inside Grabio, so it is different from Grabio’s fully on-device tools like the M4A converter.

VERT is a free tool, and per the table above it describes its audio conversion as running on your device. If you want to stay entirely inside Grabio’s own on-device tools, convert to M4A instead.

Convert audio to MP3 on iPhone: FAQ

Why does Grabio use VERT instead of converting MP3 itself?

Apple’s Shortcuts app simply doesn’t include an action that encodes audio as MP3. Grabio only builds tools it can genuinely deliver, so for MP3 specifically it routes you to VERT rather than faking a conversion it can’t actually do.

Is converting to M4A instead of MP3 a better option?

If the app or device you’re sending the file to accepts M4A, yes, that conversion runs fully on your iPhone with no outside service at all. MP3 is still the more universally compatible format for older car stereos, some Android devices, and certain software, so it’s worth it when you specifically need an MP3.

Do I have to select the file manually on VERT?

Yes. iOS doesn’t allow any app, including Grabio, to automatically place a file into a website’s upload box. You’ll need to tap the upload area on VERT and pick your audio file from the picker yourself, this is a one-time extra tap, not a bug in Grabio.

Related on iPhone: convert audio to M4A on iPhone, extract audio from a video on iPhone, MP3 vs M4A compared, convert MP4 to MP3 on iPhone, or Video & Audio Tools.

Video downloading is the other half of what Grabio handles for free, see the full video downloader for iPhone comparison if that is ever what you need next.