Confused about a blue line

• Apr 2, 2024 - 09:43

I'm notating a piano score. When I try to play it back a blue vertical line appears at the beginning of the music and it won't play. I have searched the handbook and have been going through the lessons but so far I can't find any mention of it. What did I do wrong and how do I fix it? I have another score I'm working on and I have no problems playing it back. Thanks


Please Include score. This may be one case where also including a screenshot might actually be useful.

The only blue line I can think of at the beginning of a score would indicate that you were in Note Entry mode there at the beginning, but you can play when that is the case.

" When I try to play it back a blue vertical line appears at the beginning of the music and it won't play"

I think that you have selected the first measure - and then accidentally clicked the Toggle loop playback button instead of the Play button. Turn off Loop playback, and your score should play normally when you click the Play button..

In reply to by bobjp

Sometimes when I first start Musescore (4.2.1) the sound fonts fail to load and if I then hit play I get a static blue line at the start of the score as described by the OP. If I look in the mixer there are no soundfonts available, not even Musescore Basic. If I close and restart Musescore the sound fonts load and everything works normally.

I think it is something to do with caching on my PC (HP Pavilion, Win 10, Intel(R) Core(TM) i5-3210M CPU @ 2.50GHz, 8GB RAM, 1Tb HD, no SSD) as apps are often very slow to load on the the first attempt but much quicker a second time around. However, I haven't yet found a magic setting in Windows to fix this. As software has bloated somewhat in the 10 years since I bought it and it is beginning to wheeze and struggle to keep up I am thinking I should put it into retirement and get a new one but it sill just about copes with MU4.

In reply to by SteveBlower

I've had the same problem when the audio device doesn't initialise properly, so MuseScore doesn't know which output to use (usually when I've plugged headphones in just before starting MuseScore). Closing MuseScore, making sure I have the right output device selected, and starting MuseScore again, always fixes it for me.

In reply to by jscaranomusic

I think that's a problem (a delay) of the loading audio samples.
This has sometimes happened to me by opening the score and starting playback immediately (too fast!) on a computer, which probably lacks memory and speed... (it's the case on one of mine)
The clue to watch out for is the loading audio samples bar at bottom left under the palettes panel - see images below. This progress bar can be gone quickly (which is almost always the case, fortunately!), so it's easy to miss.
To resolve the issue: quit, reopen the score and check that the audio samples have been fully loaded before launching playback.


  • Loading audio samples bar in progress (image below)


In reply to by cadiz1

I have considered opening a Git hub issue for this failure/delay to load but a) I can't reproduce it consistently; b) my PC doesn't meet the published required specification; c) it is only a minor irritation with a simple remedy.

If someone else can reproduce it on a PC that meets the specs, it would be useful if they could raise the issue on Git hub.

In reply to by cadiz1

Mine might be a different issue. I've still had the problem even when I wait till after the samples are loaded, and the fix seems to be in my system audio settings, not in MuseScore. There's no audio device selected in the I/O setting in MuseScore preferences, but I think that's because Windows is giving MuseScore incorrect information on start-up.

Thanks so much for all the help. It's going to take awhile to learn everything. I have so much to learn. After I left the first message I opened up the score again and the blue line was gone and it played accurately - so yes, I think it's wires got crossed. I realized it was the line that travels through the music as it plays. Have a great day!

In reply to by SonniQ

This is not a bug. Sounds have to load before the score will play. The farther away the computer is from recommend (not just minimum) specs, the longer that will take. The size of the score can make a difference.

Make sure not to change audio devices while MU4 is open. Go through all the settings for each device you use, so that the computer will use those settings for them.

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