MOV: Apple's video format
MOV is the QuickTime container created by Apple. Every iPhone and iPad video, and many Mac screen recordings, are MOV files. Inside, the picture is usually HEVC and the sound AAC — fine on Apple devices, but often a problem on Windows PCs, Android phones and car radios.
Why extract the sound of a MOV
To keep the audio of a concert, a speech or a family moment, send a voice recording without the heavy video, transcribe an interview, or reuse the soundtrack in an edit. The MP3 plays everywhere and weighs a fraction of the original MOV.
Private by design
iPhone videos are often personal. Here the MOV is never uploaded: FFmpeg runs in your browser and reads the file on your device. You can even convert with the phone in airplane mode once the page is loaded.