What happens when a video becomes an MP3
An MP4 file is a container with two streams in it, the picture and the sound. To get an MP3, the sound stream is taken out, decoded and encoded again as MP3, and the picture is thrown away. Almost all phone and camera videos store their sound as AAC, which isn't MP3, so a converter can't just copy it across. That's why every MP4 to MP3 tool re-encodes, and why the bitrate it picks matters.
This one reads only the sound stream and never decodes the picture. A 60-second, 60.8 MB phone video took 1.0 second to become a 1.2 MB MP3 in our test, and the MP3 lasted exactly as long as the video's sound track, to the sample. iPhone clips in MOV format work the same way, including HEVC ones that Windows can't play without an extra codec: the picture is never touched, so its format doesn't matter.
A bitrate that matches the video's sound
Each result shows what the video's sound track is: its codec, channels, sample rate and bitrate. Phone and camera videos usually carry AAC sound somewhere between 96 and 256 kbps, and AAC sounds better than MP3 at the same bitrate. Match the video's sound takes that number, adds about a quarter for MP3's lower efficiency and rounds up to a standard setting. A 128 kbps phone video gets a 160 kbps MP3.
Picking 320 kbps for the same video doubled the MP3's size in our test (482 KB instead of 241 KB for 12 seconds) without adding anything, because the sound can't be better than what the video recorded. The result line says so when you choose a much higher setting than the sound needs.
| Video's sound | MP3 it gets | MP3 size per minute |
|---|---|---|
| AAC 96 kbps | 128 kbps | 0.96 MB |
| AAC 128 kbps | 160 kbps | 1.2 MB |
| AAC 192 kbps | 256 kbps | 1.92 MB |
| AAC 256 kbps | 320 kbps | 2.4 MB |
| Uncompressed or lossless sound | 256 kbps | 1.92 MB |
For a lecture, sermon, interview or meeting recording, choose Mono: speech doesn't need two channels, and the MP3 is half the size. Our 12-second clip went from 241 KB to 121 KB.
When you don't need MP3 at all
If what you want is the sound with no loss whatsoever, and the place you're sending it accepts M4A or AAC files (iPhones, Macs and most music players and editors do), Extract Audio from Video copies the sound track out byte for byte, without re-encoding. Use MP3 when something specifically asks for it: an older car stereo, a podcast host, a ringtone app, an upload form that lists only ".mp3".
Videos with no sound
Screen recordings made without the microphone, and clips exported with the audio turned off, have no sound track at all. Some converters still produce a silent MP3 from them, or fail with a generic error. Here the result says right away that the video has no sound track, so you know to go back to the source rather than wonder why the MP3 is empty.
Your videos stay on your device
The video is read and the MP3 is encoded inside your browser, with a WebAssembly build of the LAME encoder. Nothing is uploaded, there's no account or size limit, and because the picture is skipped, even long videos are quick. Several videos can be converted at once and downloaded as a ZIP. To cut the MP3 shorter afterwards, use Trim Audio, which cuts MP3s without re-encoding them again.