What is an MP3 file?
MP3 is the audio format that made digital music portable. Standardised in 1993, it compresses sound by discarding frequencies the ear masks or cannot hear, shrinking a CD track to a tenth of its size. Every device made in the last quarter century plays it: phones, cars, TVs, smart speakers, browsers, and every editor and messaging app.
Which bitrate?
128 kbps is small and fine for speech and podcasts. 192 kbps is transparent for most music and listeners. 256 and 320 kbps are for the highest quality, at a cost of larger files. Converting from a lossless source such as WAV or FLAC at 320 kbps is effectively indistinguishable from the original; converting from another lossy format loses a little more each time.
MP3 versus the alternatives
AAC (M4A) sounds slightly better at the same bitrate and is Apple's default. OGG Vorbis is what games and open-source apps prefer. WAV and FLAC are lossless for editing and archiving. MP3 wins on one thing only, and it is the thing that matters most: it plays absolutely everywhere.
Frequently asked questions
How do I get the audio out of a video?
Use the MP4 to MP3 tool; it accepts MOV, MKV, WebM, and AVI too and extracts the soundtrack in seconds.
Does converting MP3 to WAV improve quality?
No. It only stops further loss. Detail discarded by the MP3 encoder cannot be recovered.