Audio Converter

What actually happens when you press Convert

This page loads FFmpeg compiled to WebAssembly. The engine core is about 32 MB, it downloads once and your browser caches it, which is why the first run pauses before anything happens and later runs start almost immediately.

Your file is then decoded and re-encoded with a specific command depending on the output you chose. MP3 goes through the LAME encoder at the constant bitrate in the dropdown. OGG goes through Vorbis at quality scale 5, which lands around 160 kbps on typical music. WAV is written as 16-bit little-endian PCM, which means no compression at all. Everything runs in your browser, so your files never leave your device.

Bitrate in numbers you can check yourself

Bitrate is simply how many bits of data each second of audio is allowed to use. Divide by eight and you have bytes per second, which makes the maths easy.

• 128 kbps works out to 16 kB per second, so roughly 0.94 MB per minute.
• 192 kbps is 24 kB per second, about 1.4 MB per minute.
• 256 kbps is 32 kB per second, about 1.9 MB per minute.
• 320 kbps is 40 kB per second, about 2.4 MB per minute.

Take a four minute song. At 128 kbps you get a file near 3.8 MB, at 192 kbps near 5.8 MB, and at 320 kbps near 9.6 MB. A 45 minute interview lands near 42 MB at 128 kbps, which is usually plenty for speech, and near 108 MB at 320 kbps, which is mostly wasted space.

For reference, the WAV option is not compressed. A stereo 44.1 kHz 16-bit WAV runs at 1411 kbps, or roughly 10 MB per minute. A three minute track becomes about 30 MB.

Picking an output format

Choose MP3 when the file has to play anywhere without question: car stereos, older phones, podcast hosts, school laptops, church sound desks. It is the safest format in existence and the least likely to be refused by an upload form.

Choose WAV when the file is heading into an editor rather than a player. Audio editors, video timelines, sampler instruments and many transcription pipelines prefer uncompressed PCM because they can scrub and cut it without decoding overhead. WAV is also the right answer if you plan to do more editing and export again later, since every extra MP3 round trip throws away a little more detail.

Choose OGG when you are feeding a game engine, a web player or an open-source toolchain. Vorbis is patent-free, and at quality 5 it generally sounds cleaner than an MP3 of the same size.

Re-encoding only ever removes information

MP3, OGG and AAC are lossy. They throw away parts of the signal a listener is unlikely to notice, and once that data is gone it cannot be recovered. Converting a 128 kbps MP3 to a 320 kbps MP3 does not restore anything. It re-encodes what is left at a more generous budget and gives you a file nearly three times larger that sounds slightly worse than the original, because the second pass introduces its own errors on top of the first.

Converting a lossy file to WAV is the same trap. The WAV is lossless, but it is a lossless copy of already-damaged audio.

Going the other direction is where this tool shines. A FLAC or WAV master converted to 320 kbps MP3 loses very little that most people can hear on normal equipment, and the file shrinks by roughly eighty per cent.

Speed, memory and the 200 MB warning

WebAssembly runs inside the browser sandbox with no access to the CPU features native FFmpeg uses freely, so expect conversion to take several times longer than the same job on a desktop command line. For a typical song the difference is a few seconds against a fraction of a second, which nobody notices. For a two hour recording it is the difference between a short wait and a long one.

Memory is the harder limit. The whole input has to sit in the tab's memory alongside the decoded audio and the output buffer, and a browser tab is usually capped well below the machine's real RAM. That is why the page warns above 200 MB. Mobile browsers are stricter again and will often kill the tab rather than report an error. If a large file fails, a desktop browser is the first thing to try.

The tool takes one file at a time and only accepts MP3, WAV, OGG, M4A and FLAC as inputs. If you drop a video in, use MP4 to MP3 instead, which is built for pulling an audio track out of a video container.

Questions people ask

Why does the first conversion sit there doing nothing?

It is downloading the roughly 32 MB FFmpeg core from a CDN. On a slow connection this can take twenty or thirty seconds. Once it is cached, the next conversion in the same browser starts straight away.

Can I convert an M4A or FLAC to MP3?

Yes. Both are accepted as inputs. M4A usually contains AAC audio, and FLAC is lossless, so a FLAC to MP3 conversion at 256 or 320 kbps is a sensible way to shrink a large library for a phone.

Why is my WAV file so much bigger than the MP3 I started with?

WAV stores raw samples with no compression. Going from a 5 MB MP3 to a 50 MB WAV is normal and expected. The extra size is padding, not quality.

Does it keep the artist and album tags?

Metadata handling depends on the source and target format and should not be relied on. Check the tags in your music player after converting and fix them there if they matter.

What should I use for a long recording I need in text?

Convert to a compact MP3 first if the file is huge, then run it through Transcribe Audio. For editing loudness and levels on a spoken-word recording, Audiobook Mastering is the better starting point.