> I would like to download the videoes, not only stream youtube-viewer can download.
Some more things to try: Do the videos play properly in mpv? While this is a slightly different situation, I've found that with mps-youtube I get only audio in vlc but it works fine with mpv. Does the video download properly with youtube-dl? If something can be downloaded with youtube-dl and not avideo it may have something to do with proprietary JavaScript.
