It is not possible to change resolution for rtmp stream, apart from resizing a player.
Get hls stream with streamlink or youtube-dl.
C:\streamlink.exe
https://chaturbate.com/sassy3va/
[console][info] Found matching plugin chaturbate for URL
https://chaturbate.com/sassy3va/
[plugin.chaturbate][info] Stream status: public
Available streams: 240p (worst), 360p, 480p, 576p, 720p, 1080p (best)
C:\>youtube-dl.exe -F
https://chaturbate.com/sassy3va/
[Chaturbate] sassy3va: Downloading webpage
[Chaturbate] sassy3va: Downloading m3u8 information
[info] Available formats for sassy3va:
format code extension resolution note
slow-0 mp4 426x240 488k , avc1.66.21, mp4a.40.2
slow-1 mp4 640x360 928k , avc1.66.30, mp4a.40.2
slow-2 mp4 854x480 1258k , avc1.77.31, mp4a.40.2
slow-3 mp4 1024x576 2076k , avc1.77.31, mp4a.40.2
slow-4 mp4 1280x720 3396k , avc1.77.31, mp4a.40.2
slow-5 mp4 1920x1080 5628k , avc1.100.40, mp4a.40.2 (best)