Reviewed 2026-10-20 by the Spool editorial team · How we test
What MP4 to MP3 conversion actually does
An MP4 file is a container with at least two streams inside: a picture stream (usually H.264 or HEVC) and a sound stream (almost always AAC). Converting to MP3 throws the picture away and re-encodes the sound with the LAME MP3 encoder at the bitrate you pick. The default is 192 kbps constant bitrate, a safe middle ground for both music and speech. Title, artist and other text tags in the MP4 are copied into ID3v2.3 tags in the MP3.
Because AAC and MP3 are different codecs, the audio is always re-encoded. That's a second round of lossy compression, so choose a bitrate at least as high as the source's. Phone videos typically carry AAC at 128–256 kbps; at 192 kbps or more the difference from the original is hard to hear.
Choosing a bitrate and the other settings
| Setting | Options | When to change it |
|---|---|---|
| Audio bitrate | 64–320 kbps | 320 for music you'll keep; 128 for talks and lectures; 64 for long voice recordings |
| Channels | Original or Mono | Mono halves the information to encode, so speech stays clearer at low bitrates. Use it for interviews, lectures and voice notes. |
| Sample rate | Original, 48, 44.1 or 22 kHz | Leave it on Original unless a device or service asks for 44.1 kHz specifically |
MP3 file size depends only on bitrate and length: about 1 MB per minute at 128 kbps, 1.4 MB at 192 kbps and 2.4 MB at 320 kbps. A one-hour lecture at 64 kbps mono is under 30 MB.
MP3, M4A or WAV?
- MP3 plays on every device ever made with a speaker, including old car stereos and cheap MP3 players. Pick it when compatibility matters most.
- M4A keeps the audio as AAC, the same family as the MP4's soundtrack. It sounds slightly better than MP3 at the same bitrate and plays natively on iPhone, Mac, Android and Windows.
- WAV is uncompressed. Use it when you'll edit the audio in a DAW or video editor and want to avoid another lossy step. It's about 10 MB per minute.
Typical uses
- Lectures, webinars and Zoom recordings: listen on a commute without the video eating your data. Mono at 96 kbps is plenty.
- Your own music videos or performances: get a track you can upload to SoundCloud or a podcast host.
- Voice-overs and interviews recorded on a phone camera: extract, then normalize the loudness or cut the part you need.
- Ringtones: convert, then use the ringtone maker to pick 30 seconds.
On your phone
iPhone: tap the drop area and choose Photo Library to pick a video from Photos, or Choose File for the Files app. iOS may say "Preparing" for a moment while it exports the video; large 4K videos take longer to hand over. The MP3 saves to Files → Downloads.
Android: pick the video from Files or your gallery; the MP3 goes to the Download folder.
Limits and edge cases
- Files up to 100 MB total and 10 minutes long; up to 10 files per batch.
- If the MP4 has several audio tracks (for example two languages), we convert the first one.
- Screen recordings without sound give the message that the file has no audio. Check the original plays with sound.
- Browser processing uses original files on your device. Public-link downloading is unavailable.
Privacy
Convert and edit files on your device. The browser edition accepts up to 100 MB total, media up to 10 minutes and video up to 4K. Codec availability and device memory can limit individual jobs.