My previous approach to saving bandwidth on youtube videos was to request the lowest-resolution versions possible.
That is a simple approach but leaves some MB on the table. The absolute lowest bandwidth video is achieved by picking the lowest bitrate audio and video even if they occur in separate files.
Consider this 42min video about the history of helicopters.
# request lowest resolution first # youtube-dl -f '160/278/133/18/22' [url] <strong>196940618</strong> World_s_First_Helicopter_-_Prehistoric-JE1iOzDcibs.mp4 # youtube-dl -f 'worstaudio+worstvideo' [url] <strong>45369327</strong> World_s_First_Helicopter_-_Prehistoric-JE1iOzDcibs.webm
192MB vs 44MB is a very real difference.