I believe this is due to Firefox playing ~70ms samples of audio at original speed, and skipping between them. In my experience with a similar effect in mplayer (https://mplayerhq.hu/), blending samples of about 15ms produces quality comparable to Webkit (Chrome, Opera).
`mplayer -speed 2 -af scaletempo=stride=15:overlap=1 <media_file_or_url> # better quality`
Note that using `]` to speed up greater than 3x, the words are still intelligible in the latter method. BTW: "overlap=1" causes the samples to be blended together across their entire duration.
I believe this is due to Firefox playing ~70ms samples of audio at original speed, and skipping between them. In my experience with a similar effect in mplayer (https:/ /mplayerhq. hu/), blending samples of about 15ms produces quality comparable to Webkit (Chrome, Opera).
To test this yourself in Firefox and mplayer:
video: https:/ /www.youtube. com/watch? v=K0Tsa3smr1w /r1---sn- n4v7sn7y. googlevideo. com/videoplayba ck?id=o- AKrDYrKDiSnXJpe ZyZF5pIoHpfZrgI KmRSc2E2753l3m& itag=250& source= youtube& requiressl= yes&mm= 31%2C29& mn=sn-n4v7sn7y% 2Csn-n4v7knlk& ms=au%2Crdu& mv=m&pl= 18&ei=4vTNXNDJB 4WQkwag0KugCg& initcwndbps= 2038750& mime=audio% 2Fwebm& gir=yes& clen=15794557& dur=2131. 221&lmt= 150796473071757 6&mt=1557001371 &fvip=1& keepalive= yes&c=WEB& ip=205. 154.192. 198&ipbits= 0&expire= 1557023042& sparams= ip%2Cipbits% 2Cexpire% 2Cid%2Citag% 2Csource% 2Crequiressl% 2Cmm%2Cmn% 2Cms%2Cmv% 2Cpl%2Cei% 2Cinitcwndbps% 2Cmime% 2Cgir%2Cclen% 2Cdur%2Clmt& signature= 4BB77D089E75903 DF0EB3B66A4C361 39C0BA2B61. 92C7BDB33502808 BADBCD64236905E BB1B8CBEDF& key=yt8& ratebypass= yes) for same video (retrieved with youtube-dl -j K0Tsa3smr1w)
["DASH Audio" stream URL](https:/
`mplayer -speed 2 -af scaletempo= stride= 70 <media_file_or_url> # present Firefox quality`
`mplayer -speed 2 -af scaletempo= stride= 15:overlap= 1 <media_file_or_url> # better quality`
Note that using `]` to speed up greater than 3x, the words are still intelligible in the latter method. BTW: "overlap=1" causes the samples to be blended together across their entire duration.