What this tool does
A voice memo that will not play in the car, an editor that only accepts WAV, a FLAC album too large to send in a chat: this tool turns audio files into MP3, M4A, WAV, FLAC or OGG. Drop in several at once and they are converted one after another with the same settings; save each result on its own or all of them as one ZIP.
Before anything is converted, each file shows its length, codec, sample rate and approximate bitrate. When the format you pick already holds the file's own codec — an AAC recording saved as M4A, for example — the sound is not decoded and compressed again. The packets are moved into the new container as they are, then compared one by one with the original, and the page tells you when every one of them matches.
How to use it
- Press "Choose audio files" or drag files onto the box. MP3, M4A, WAV, FLAC, OGG and the sound of video files can all be opened.
- Pick the format to save. MP3, M4A and OGG also take a quality (bitrate); WAV and FLAC keep the sound untouched, so there is nothing to choose.
- If needed, open "More options" for the sample rate, mono, or a part of the file (start and end). Left empty, everything stays as it was.
- Press Convert. Each file shows a progress bar, and when it is done you can listen to it right away and save it.
Which format should I pick?
If you are not sure where the file will be played, MP3 is the safe choice: phones, car stereos and old players all handle it. M4A (AAC) sounds slightly better than MP3 at the same size and fits iPhones and Macs especially well. OGG (Opus) packs speech into very small files, but some older devices and car stereos cannot play it.
WAV is uncompressed, the raw shape of the sound, which is why editors and broadcast systems often ask for it; it takes about 10 MB per minute. FLAC holds exactly the same sound without any loss in roughly half the space. For an archive FLAC is a good fit; for sending to other people, MP3 or M4A.
Sample rate, bit depth and mono
Most music is made at 44.1 kHz and most video sound at 48 kHz. Keeping the original rate is nearly always right; change it only when a device or an upload form asks for a particular one. A 96 kHz, 24-bit recording keeps its 24 bits when saved as WAV or FLAC here, while MP3 tops out at 48 kHz and Opus always runs at 48 kHz.
Mono folds both channels into one. Interviews, voice notes and dictation lose almost nothing by it. WAV and FLAC shrink to about half; for MP3, M4A and OGG the size follows the bitrate, so turn on mono and pick one step lower for the same clarity in less space. Music, with instruments spread left and right, is better left in stereo.
When conversion cannot improve the sound
Lossy audio — MP3, AAC, Opus — has already dropped detail that cannot be rebuilt. Saving an MP3 as WAV or FLAC therefore only multiplies its size, and picking 320 kbps for a 128 kbps original does the same. The page flags both before you start; keep them for programs that insist on one format.
Going from WAV to FLAC and back is lossless. In our tests a WAV turned into FLAC and back into WAV came out with every sample identical to the original.
Codec versus container
The ending of a file name names the container — the box — not always what is inside it. An .m4a or .mp4 usually holds AAC, a .webm or .ogg often Opus, a .wav plain PCM samples. When only the box changes and the codec stays, nothing needs decoding: that is why moving an AAC voice memo from .mp4 into .m4a takes a moment and keeps every bit.
Your data
Files are opened with the browser's file reader and processed only on this device. Nothing is uploaded, and no request carrying sound leaves the page. The MP3 and FLAC encoders, and an AAC encoder for browsers without one of their own, are fetched once from this site the first time that format is written. This browser remembers only the chosen format, quality, sample rate and mono setting.
Questions and answers
I picked M4A and it says “original sound moved over”.
The original was already AAC, so there was no need to encode it again. Decoding and compressing sound again costs a little quality each time, so a file in the same codec is moved into the new container untouched. If the original's bitrate is above the quality you picked, it is encoded again to make it smaller.
Why can't I select OGG?
This tool writes OGG (Opus) only with the browser's built-in encoder. When the browser you are using has none, OGG is switched off. Current Chrome, Edge and Firefox usually have it.
Can I put in a video file?
Yes. Only the sound of the video is taken and converted to the format you pick. If pulling the sound out of videos is what you mostly need, the MP4 to MP3 tool can also copy the original sound out without encoding it again.
Are the title, artist and cover kept?
Yes, wherever the new format has room for them. MP3, M4A, FLAC and OGG carry the title, artist, album and cover picture over; WAV keeps the text but has no place for a picture. WAV tags written in UTF-8 or in the Korean CP949 code page come out readable instead of as stray symbols.
