I use a HDMI connection to my monitor with speakers. When playing a score in
Musescore the sound is delayed by about 1 second compared to the the activity
on the screen. The note in score which is played is highlighted.
When changing the sound device in the tab "I/O" in Musescore from PulseAudio to
ALSA audio, sound and picture are in sync. This suggests that pulseaudio is
delaying the sound. "I/O" is reached by selecting Edit->Preferences...
I noticed earlier also this type of delay when playing a video in Firefox,
however currently this is no longer the case. It was most apparent when a
person is speaking in the video.