Thus, a file containing opus 251 was likely downloaded from YouTube (via yt-dlp) with video in AV1 format 399. YouTube’s itags:
"There's your problem," Kael said, tapping the screen. "The audio isn't missing; it’s hidden in a wrapper. It’s an ultra-low bitrate trick. They used a 'New' flag on the header to confuse legacy players." codecs av01008m08 399 opus 251 new
<Codec>av01.0.08M.08</Codec> <!-- Bitrate 399000 bps, audio opus itag 251 --> Thus, a file containing opus 251 was likely
: This specific itag represents Opus audio, usually delivered at a variable bitrate (VBR) peaking around sample rate. Efficiency " Kael said