A MOV file is more than its extension
MOV is the QuickTime container associated with Apple video workflows. Camera footage and screen recordings can store picture and sound inside it, using different codecs. The file extension therefore does not guarantee that a browser can read its audio. For this extraction, the important part is a usable soundtrack. You do not need a new video export just to listen to an interview, but you do need source audio that the local media parser and conversion process can handle.
MP3 trades audio detail for a smaller file
MP3 uses lossy compression to make an audio file easier to store and share. It contains no video frames, which removes a large part of a typical camera recording. The remaining size depends mainly on duration and bitrate. This page offers 128, 192, and 320 kbps, with 192 selected initially. Use the result player to compare speech and music with your source. A higher bitrate cannot undo distortion, clipping, or compression that was already present in the MOV.
The output contains the soundtrack, not separate voices
The engine discards video for the audio export and requests the selected output format. When the source audio uses a different codec, creating MP3 requires conversion. Sounds already mixed together remain together: extracting an interview does not remove background music or isolate a speaker. The source MOV is not overwritten. Keep it alongside the download if you may need to return to the picture, sync the recording in another edit, or make a different audio copy later.
Pick WAV for a working copy when needed
WAV is also available in the format controls when a receiving editor asks for uncompressed audio. Its larger size buys an uncompressed output format, not a better original recording. For a rehearsal you only want to hear, an MP3 may be enough; for another round of audio editing, WAV avoids another lossy output encode. Check the receiving app before choosing. If the MOV has no readable audio track, changing the output choice cannot create the missing sound.