MP3 Converter

Sound files in WAV, M4A and AAC, FLAC and Ogg (Vorbis or Opus), and the sound of videos in MP4, MOV, MKV and WebM. Each file says what it holds as soon as you add it, before anything runs, so you can see what you will get.

A video’s picture is left behind and only its sound becomes the MP3. If a film has several sound tracks, the first one that can be decoded is used, and the file says so. A file that is already an MP3 has nothing to convert, so it is left alone, and so is a video with no sound at all.

A few sound formats can’t be read yet: Dolby Digital and DTS, which films carry, WMA, and AIFF. Those say so in their row instead of being turned into something broken.

Standard is 128 kbps, about 1 MB a minute. High is 192 kbps, about 1.4 MB a minute, and is where the page starts. Best is 320 kbps, about 2.4 MB a minute, the most MP3 can hold. Our 4-minute test track came out at 3.8 MB, 5.8 MB and 9.6 MB.

Most sound that is sent here is compressed already, a phone’s M4A or the AAC in a video, and each compressed copy loses a little. At 128 kbps cymbals and strings start to show it; at 192 most people can’t hear it, and the file is still small enough to mail. Take Best when you want the least loss, and Standard for speech.

Mono recordings, such as a voice memo, are kept mono and made at half the bitrate you pick, because their one channel gets as many bits as each channel of a stereo song. A recording at a rate MP3 doesn’t have, such as 96 kHz, is brought to the nearest one, 48 kHz.

A 4-minute song becomes an MP3 in about 1 second from a WAV and about 2 seconds from an M4A, and a 60-minute recording in about 19 seconds, on a recent laptop.

Your file is read a piece at a time and the MP3 is written to your browser’s private storage as it goes, so a long recording doesn’t have to fit in memory. The browser’s memory grew by up to about 250 MB while it ran. Safari before version 26 is the exception, as the section below says. We haven’t measured phones, so we promise no length there.

Title, artist, album and cover art come along into the MP3 where the file has them. WAV files have none to carry.

The MP3 also records how much silence the encoder added at each end, in the tag LAME writes first. Players that read it, such as Apple’s audio software and ffmpeg, play the song at its real length and without a gap between tracks, which a plain conversion can’t promise.

In Chrome, Edge and Firefox, and in Safari 26 or later, the browser’s own codecs decode AAC, FLAC, Ogg and the rest one piece at a time, so there is no length limit of ours (we tried a 60-minute recording). WAV needs no codec at all, so it works everywhere.

Safari before 26 has no such decoder, and in WebKit, Safari’s engine, FLAC decoding failed on every file we tried. In those cases ToolHero asks the browser to decode the whole file at once, which holds all of it in memory, so it works for sound up to 10 minutes long and says so when a file is longer. The tags of a file decoded that way are not kept.