App or browser: which audio converter you actually want

They searched for an app, often because they want something that works offline or on files already on their phone. They deserve to know that a browser tab does most of this with no install — and where it genuinely falls down.

Install an app if the recording is already on your phone, you are on cellular data, or you need to work with no signal at all. Use a browser tab for everything else: it reads far more formats, has no per-file counter, and can copy the audio across without re-encoding it, which app-store converters generally cannot. On Android both routes convert today. On an iPhone the honest answer is Safari, which handles the whole job with nothing installed. Neither route sends your file anywhere, and that is worth checking for yourself rather than believing either of us.

The short answer, by situation

Most people arrive with one file and one deadline, so start with the row that matches.

What a browser tab genuinely does better

The converter on this site is FFmpeg compiled to WebAssembly — the engine most desktop audio software has relied on for decades, running inside the page. That has four consequences an app-store converter usually cannot match.

It reads almost anything. MP3, M4A, M4B, AAC, WAV, FLAC, OGG, Opus, WMA, AIFF, CAF, ALAC, AMR, AC-3, MP2, MKA, WavPack, APE, AU — and the audio track inside MP4, MOV, MKV, WebM, AVI, WMV, FLV and 3GP. A WhatsApp voice note arrives as Opus, and Opus decodes here without fuss. Most phone converters simply will not open one.

It writes more than four formats. MP3, M4A, AAC, WAV at 16- and 24-bit, FLAC, ALAC, OGG Vorbis, AIFF, WMA and .m4r for an iPhone ringtone. One deliberate gap: there is no Opus output, because libopus crashes this WebAssembly build and substituting a weaker encoder without saying so would be dishonest. Opus files go in fine; they just come out as something else.

Some conversions never touch an encoder. When the compressed audio is already legal inside the container you asked for, it is carried across untouched: AAC inside an .m4a going to .m4a, .aac or .m4r, the AAC soundtrack of an .mp4 coming out as .m4a, MP3 to MP3, ALAC to ALAC. Because nothing is decoded and nothing is compressed, those finish in roughly a second regardless of length, and the audio is identical — every compressed byte of the stream and every decoded sample. The container's metadata is rewritten, so the file itself is not a clone, but the sound is untouched. An app that decodes to samples and re-encodes cannot offer that, and ours does not.

Nothing is metered. There is no server keeping count, because there is no server. Free converters that run on somebody's machine have to charge for it eventually, usually through a per-file size cap and a daily job budget. The shape of a free audio converter's limits explains how to find the real figure for whichever service stopped you, since the numbers repeated across the web are frequently stale.

What an installed app genuinely does better

Three things, and they are real.

It is already where the files are. On a phone, the file you want is usually in a recording app, a chat thread or the camera roll. A browser tab can reach all of them through the system file picker, but the app skips a step and never loses the file to a share sheet.

It works with no network. Once installed, an app's converter is on the device. A browser tab can also convert offline, but only if the page and the 32 MB engine are already in the cache from an earlier visit. Land on a converter site for the first time in airplane mode and nothing happens.

It does not spend 32 MB of your data allowance. That is the strongest argument for installing something, though it applies only once per browser per year.

The 32 MB engine, and when you pay for it

This is the browser route's only real cost. The first time you open the converter, the page fetches the FFmpeg WebAssembly core: roughly 32 MB, served from this site rather than a CDN, and cached by the browser for a year. On home Wi-Fi you will barely notice. On a weak cellular connection it is a genuine wait, and it is the reason the app exists.

After that first fetch the page starts working immediately, and the conversion itself makes no network requests at all. You can verify that in about a minute: open the Network panel, run a job, and watch it stay empty — or disconnect your Wi-Fi after the page has loaded and convert anyway. How to check whether a converter really keeps your file local walks through both tests, and they work on any site making the same promise, not only this one.

Phone memory: the browser's real ceiling

The WebAssembly here is 32-bit, so it has a hard address space of about 2 GB, and audio work wants roughly three times the file's size resident while it runs. The converter warns above 300 MB and refuses above 2 GB rather than crashing halfway through.

For compressed audio that is enormously generous — five hours of 128 kbps stereo is about 300 MB. For uncompressed audio it is not: 16-bit 44.1 kHz stereo WAV runs about 10.6 MB a minute, so half an hour of it is already at the warning line. Watch the output side as well as the input. A 200 MB MP3 is comfortable; the same recording written out as WAV is around 2 GB, and that is the side that fails. When a converter says your file is too big has the arithmetic and the ways round it.

A native app has the phone's whole memory allocator to work with, so it does not hit that wall. In practice it matters for multi-hour lossless recordings and almost nothing else.

What our app does, and what it does not do today

Audio Converter — m4a to mp3 is free to install on the App Store and on Google Play. Stated plainly, including the part that does not flatter it:

• On Android 1.0 it converts MP3 or WAV input to MP3 at 128, 192, 256 or 320 kbps. Other source and output formats belong in the browser converter for now.
• On iOS the conversion path is guarded off in the code and returns an error. The app on an iPhone is an audio editor, and a capable one, but it will not currently change your file's format. Use Safari for that; the iPhone guide covers the routes, including the Shortcuts trap.
• Thirteen editing tools work on both platforms — cut, compress, fade, reverse, merge, loop, speed, volume, normalize, stereo to mono, bass boost, echo — plus a recorder, a player and a history of finished jobs you can share again. They all write 16-bit WAV.
• Two honest caveats on those tools. The app's speed change is a resample, so it shifts pitch with tempo; the website uses a time-stretcher, which does not. And the app's normalize is peak normalisation, which sets the loudest sample to full scale — not loudness matching, so two tracks normalised this way can still feel very different in volume.

If you are on Android and the source is MP3 or WAV, the app is the shorter path. For M4A and other formats, use the browser converter. Converting M4A to MP3 on Android covers that route, including where Chrome puts the finished file and why the APK mirror sites ranking above it are worth avoiding.

The pricing, stated plainly

The Android app is free to install and use, with no Pro tier, conversion counter, subscription prompt or in-app purchase. The iOS app keeps the existing model: one free conversion, then the second opens the subscription paywall. That platform split should be clear before you install rather than after you have picked your file.

The converter on this site has no account, no counter and no subscription. It is not generosity — there is no server bill to recover, because the work happens on your own machine. That also means there is no queue, no "please wait, position 4", and nothing for anyone to delete afterwards, because nothing was ever collected.

How to judge any converter app before installing it

Search results for a converter app are crowded with near-identical listings, and the good ones are hard to pick out. Four checks that take a minute each:

1. Read the output list, not the title. A listing that names seven formats may expose far fewer verified inputs and outputs. Ours made exactly that mistake, which is why this page prints Android 1.0's actual MP3/WAV-input, MP3-output scope rather than the store's list.
2. Check the permissions. A converter needs file access. It does not need contacts, location or your call log. Anything asking for those is monetising something other than conversion.
3. Test it in airplane mode. If it converts with the radios off, the audio genuinely stayed on the device. If it fails, your file was going somewhere — which may be fine, but you should know.
4. Distrust the quality claims. No converter can restore quality that a lossy encoder discarded. Re-encoding an MP3 at a higher bitrate produces a bigger file containing the same thinned audio. A listing that claims otherwise has told you what its other claims are worth.

Those four apply here too. The Network panel is open to anyone, the format lists above match what the engine actually writes, and the gaps — no Opus output, a 2 GB tab ceiling, an iOS build that does not convert — are on the page rather than buried in a support thread.