Pull just the soundtrack out of a video file and save it as a high-quality WAV, entirely in your browser.
The browser already knows how to play most video files, and anything it can play it can decode: this tool feeds the file to the Web Audio decoder, which extracts the audio track into raw samples, then writes those samples as a standard WAV file, uncompressed, full quality, playable everywhere and editable in any audio software. Interviews recorded as video, lectures, voice memos in video form and music from clips all become audio files without an upload to anyone's server.
Honest limits: the file must be in a format your browser can decode, MP4/H.264+AAC, WebM and most MOV files work in modern browsers; exotic codecs (some camera formats, MKV in some browsers) may not decode, and very long files consume serious memory since the whole track is decoded at once (keep it under roughly an hour). WAV output is large, about 10 MB per minute in stereo, which is the price of uncompressed fidelity; convert to MP3 afterwards with the WAV to MP3 converter on this site if size matters more.
Why WAV and not MP3 directly? Decoding gives raw samples; WAV is the faithful container for them with no second quality loss. One pass through the MP3 converter afterwards gets the smaller file without double-encoding the source's artifacts.
The video has multiple audio tracks or commentary, which is extracted? The browser decodes the file's primary/default audio track. Multi-track selection is not exposed to web pages.
Can it extract from a YouTube link? No, this works on files you have. Downloading from streaming sites is their terms-of-service question, not a file-conversion one.