Convert files to MP3

Which bit rate to choose

• Music you care about: High or Balanced. 320 kbps is the highest bit rate the MP3 format has.
• Talks, audiobooks and voice notes: Small, or Mono under More settings. Speech stays clear at a fraction of the size.
• Email and messages: Small keeps attachments light.

As it is works from what you already have. An MP3 is copied untouched, with nothing lost. A file in another compressed format keeps its own bit rate, between 128 and 320 kbps, so a 256 kbps M4A becomes a 256 kbps MP3 rather than something bigger or worse. Lossless files such as WAV and FLAC come out at 320 kbps. For any other figure, pick one from 64 to 320 kbps under More settings.

What goes in, and what comes out

Almost anything with sound in it can become an MP3: WAV, FLAC, M4A and AAC, OGG and Opus, WMA, AIFF, AMR and CAF voice memos, and videos such as MP4, MOV, MKV, AVI, WMV and WebM. From a video, only the sound is kept, taken from its first sound track.

• Channels: MP3 holds two, so a 5.1 film soundtrack is mixed down to stereo.
• Sample rate: kept as it is up to 48 kHz. A 96 kHz studio file is brought down to 48 kHz, because an MP3 gains nothing above that.
• Tags: title, artist and album come along, written as ID3v2.3, a tag version Windows and older players read well.
• Cover art: a picture stored in the source, as in many M4A and FLAC albums, is kept in the MP3.

Files with copy protection cannot be read. Everything you made or own outright, from phone recordings to old CD rips, converts as normal.

Where the MP3s go, and how much smaller they get

Under Save in, The same folder as each original puts every MP3 beside its source with the same name, so an album folder ends up holding both versions. A folder I choose… gathers them all in one place, ready to copy to a phone or to a USB stick for the car. Existing files are never replaced: a second “track 01.mp3” becomes “track 01 (2).mp3”.

The summary at the end adds it all up. A CD-quality WAV runs at 1,411 kbps, so at Balanced the MP3 is about a seventh of its size, and a folder of FLAC albums usually shrinks by more than half even at High.

For one kind of file at a time, the pages for each pair go further: WAV to MP3, M4A to MP3, FLAC to MP3, WMA to MP3, OGG to MP3, Opus to MP3, AMR to MP3 and, for videos, MP4 to MP3, MOV to MP3 and MKV to MP3.

Making room on a phone or a music player

MP3s can be converted too, which is handy when a library at 320 kbps no longer fits on a phone, an old MP3 player or a memory card. Pick MP3 and Small: each song is encoded again at 128 kbps, about two fifths of its size, so roughly two and a half times as many songs fit in the same space. As it is would only copy them, so it does not help here.

Keep the 320 kbps originals on your PC and send the smaller copies to the device, by choosing A folder I choose… under Save in. Converting from one MP3 to another always loses a little, so make the small copies from the highest-quality files you have, and never use them as the source for the next round.