SMPlayer Support Forum

I updated from 19.5 to 19.10 because a part of YouTube videos returned an error that the URL couldn't be found (again). However, the latest released version only ever finds 640*360 resolution videos, even for those that were 1280*720 in the previous version and still worked. Low resolutions are of poor quality due to low bitrate. I guess YouTube will eventually get rid of old formats, but it hasn't fully happened yet.

I can't use youtube-dl on my computer due to old OS, and adaptive streams don't ever start playing without it.

You need to enable the option "use adaptive streams" in preferences -> network. If that option doesn't work for you, send the smplayer log after trying to play a youtube video.

I looked into the log and saw that the playback stops on MPVProcess::parseLine: "Playing: ..., and it turns out that the outdated version of MPV that I must use does not support the adaptive MP4 format. I've worked around, for now, by reverting to Mplayer, although it is much less reliable overall.

I changed MPV from the one I found in one of SM packages (2015-09-23), to (2015-10-29). It is only one month younger, but works with adaptive MP4 on Windows XP.

Why does YouTube have to make changes to their formats all the time, usually towards reduction in quality...