These are encoded with Speex, the precursor to opus. If you actually want to download the audio, you can use youtube-dl to get opus encoded audio-only recording

These are encoded with Speex, the precursor to opus. If you actually want to download the audio, you can use youtube-dl to get opus encoded audio-only recordings directly: > youtube-dl -F "https://www.youtube.com/watch?v=AD4b-52jtos1" [youtube] AD4b-52jtos: Downloading webpage [youtube] AD4b-52jtos: Downloading video info webpage [info] Available formats for AD4b-52jtos: format code extension resolution note 249 webm audio only DASH audio 51k , opus @ 50k, 16.97MiB 250 webm audio only DASH audio 57k , opus @ 70k, 17.50MiB 171 webm audio only DASH audio 99k , vorbis@128k, 31.57MiB 251 webm audio only DASH audio 106k , opus @160k, 32.55MiB 140 m4a audio only DASH audio 132k , m4a_dash container, mp 4a.40.2@128k, 43.56MiB 160 mp4 194x144 144p 69k , avc1.4d400c, 30fps, video on ly, 10.50MiB 278 webm 194x144 144p 86k , webm container, vp9, 30fps, video only, 22.85MiB 133 mp4 322x240 240p 121k , avc1.4d400d, 30fps, video on ly, 17.77MiB 242 webm 322x240 240p 153k , vp9, 30fps, video only, 26.6 1MiB 18 mp4 352x262 small , avc1.42001E, mp4a.40.2@ 96k, 114. 86MiB 43 webm 640x360 medium , vp8.0, vorbis@128k, 136.89MiB (b est) The lowest quality version (opus @ 50k) is around 17mb compared with this author's 1.5mb speex version.