A video file carries a picture track and one or more sound tracks. Video to MP3 drops the picture and re-encodes the first readable sound track to MP3 with the LAME encoder, at the bitrate you choose: 128, 192, 256 or 320 kbps. MP3 plays in every music app, car stereo and editor, which makes it the easiest way to keep a talk, a voice note, a lecture or a performance as audio only.
Everything runs in your browser with FFmpeg compiled to WebAssembly. It reads MP4, MOV (including iPhone videos), M4V, WebM, MKV, AVI, 3GP, MPEG, WMV and FLV files up to 500 MB each, up to 10 per run, and keeps the title and other tags when the video has them.
Limits: the MP3 can't sound better than the video's own sound, so 320 kbps only helps when the source was high quality. Videos with no sound track, or with a sound format this engine can't read (such as Apple's spatial audio codec), are listed with the reason and skipped. Only the first sound track is saved; extra language tracks are left out.