Google Video no longer able to retrieve captions?

Captions in default language (single available or English it seems):

To get captions of a YouTube video just use this Linux command (using curl and base64):

curl -s 'https://www.youtube.com/youtubei/v1/get_transcript?key=AIzaSyAO_FJ2SlqU8Q4STEHLGCilw_Y9_11qcW8' -H 'Content-Type: application/json' --data-raw "{\"context\":{\"client\":{\"clientName\":\"WEB\",\"clientVersion\":\"2.2021111\"}},\"params\":\"$(printf '\n\x0bVIDEO_ID' | base64)\"}"

Change the VIDEO_ID parameter with the one interesting you.

Note: the key isn’t a YouTube Data API v3 one, it is the first public (tested on some computers in different countries) one coming if you curl https://www.youtube.com/ | grep AIzaSy

Note: If interested in how I reverse-engineered this YouTube feature, say it in the comments and I would write a paragraph to explain

Captions in desired language if available:

YouTube made things tricky maybe to lose you at this step, so follow me: the only thing we have to change is the params value which is base64 encoded data which is in addition to weird characters also containing base64 data which also contains weird characters.

1. Get the language initials like “ru” for russian
2. Encode \n\x00\x12\x02LANGUAGE_INITIALS\x1a\x00 in base64 with for instance A=$(printf '\n\x00\x12\x02LANGUAGE_INITIALS\x1a\x00' | base64) (don’t forget to change LANGUAGE_INITIALS to your language initials wanted ru for instance). The result for ru is CgASAnJ1GgA=
3. Encode the result as a URL by replacing the = to %3D with for instance B=$(printf %s $A | jq -sRr @uri). The result for ru is CgASAnJ1GgA%3D
4. Only if using shell commands: replace the single % to two % with for instance C=$(echo $B | sed 's/%/%%/'). The result for ru is CgASAnJ1GgA%%3D
5. Encode \n\x0bVIDEO_ID\x12\x0e$C (don’t forget to change VIDEO_ID to your video id, with $C the result of the previous step) with for instance D=$(printf "\n\x0bVIDEO_ID\x12\x0e$C" | base64). The result for ru and lo0X2ZdElQ4 is CgtsbzBYMlpkRWxRNBIOQ2dBU0FuSjFHZ0ElM0Q=
6. Use this params value from the Captions in default language section: curl -s 'https://www.youtube.com/youtubei/v1/get_transcript?key=AIzaSyAO_FJ2SlqU8Q4STEHLGCilw_Y9_11qcW8' -H 'Content-Type: application/json' --data-raw "{\"context\":{\"client\":{\"clientName\":\"WEB\",\"clientVersion\":\"2.2021111\"}},\"params\":\"$D\"}"