I use youtube-dl to stream videos from youtube. I use this format to stream/download youtube non-live videos of quality less than 720p which works fine.
youtube-dl -f 'bestvideo[height<=?720]+bestaudio' https://www.youtube.com/watch?v=ubk3dvOdYzg
But for live youtube videos
youtube-dl -f 'bestvideo[height<=?720]+bestaudio' https://www.youtube.com/watch?v=Ij2rYpNxXgM
its showing this error
ERROR: requested format not available
Your format says to take the best video-only stream below 720p and mux it together with the best audio stream. However, in this case, the live stream in question does not seem to have individual streams, just one stream with picture and audio.
To support these kinds of videos, add that format (best[height<=?720]' in your case) to your format specification:
youtube-dl -f 'bestvideo[height<=?720]+bestaudio/best[height<=?720]' Ij2rYpNxXgM
If you always want videos in 720p or less, you can also write -f 'bestvideo[height<=?720]+bestaudio/best[height<=?720]' into a configuration file so you don't have to type it out all the time.