how do I start looking for the package I need?
This happens with some mkv files and to all mp4 files I play, both with apt and flatpak installed vlc versions.
this never happened on the same computer with xubuntu 23.10
Can you check what video driver you are using? You might be on some kind of software renderer.
What does
glxinfo | grep renderer
say?
that command returns
GLX_MESA_copy_sub_buffer, GLX_MESA_query_renderer, GLX_MESA_swap_control, GLX_MESA_copy_sub_buffer, GLX_MESA_query_renderer, GLX_MESA_swap_control, Extended renderer info (GLX_MESA_query_renderer): OpenGL renderer string: Mesa Intel(R) HD Graphics 620 (KBL GT2)
This looks good.
I don't know how to figure out on vlc what sort of output method, codec, or hardware acceleration it's currently using, so I second the other person who recommended mpv.