The best frame rate for animating

My problem is this: although I have read the wiki and several discussions on setting frame rates, I have a problem I don’t see covered. I have a scene that needs to last x seconds to match the song that goes with it. I originally set my frame rate in the canvas settings to 12 fps. but I discovered that my scene, which lasts about 10-12 seconds at 12 fps, will last 40 seconds at a frame rate of 24 fps. In other words, the action in my animation slows waay down. I don’t see this mentioned in the documentation. If I set the frame rate at 18 fps, the scene lasts around 28 seconds. I make sure to set both my canvas fps and preview fps to the same number. I am trying to get an accurate length of time in seconds, that this scene lasts. Another problem I notice is that when viewing the scene in the preview monitor, the length in seconds will vary from two to five seconds, even though I haven’t changed the frame rates in either the canvas or the preview. I have timed it over an over with a stopwatch, and it varies in time length, measured in seconds. When I try to use the playback function on the synfig app itself, it crashes every time. I know this is a known problem. I just need an accurate measurement in seconds, of each scene. Any comments are welcome. Can I use a frame rate of 18 fps in the final rendering, or should it be in multiples of 12 ?

How are you changing your frame rate?
It should not change how long the animation lasts!

Synfig is time-oriented, not frame-oriented. You increase or decrease the frame rate at your choice, but the total length of animation keeps the same as before.
Maybe you have the impression of slowness when frame rate is higher due to limitations of your CPU/GPU specs.

What version of Synfig Studio are you using (1.2.2, 1.3.11, other - which?) and under what OS (Windows, Mac, Linux)?

Thanks for answering. I’m using Studio 1.3.11. I know that the fps shouldn’t affect the time the animation lasts, that’s what confuses me. But my character’s movements get really slow, the higher the frame rate. I don’t understand why. I did change the frame rate in the render options as well, but since I haven’t rendered it yet, I don’t see how that could affect anything. I understand that the frame rate should stay the same throughout the animation, I was just experimenting with the settings when I discovered this anomaly.

I have done some more experimenting, and one of the problems is with the preview monitor. It defaults to half the fps set in the canvas settings. It shouldn’t make any difference but if I set that number to the same as the number in the canvas settings, which is twelve, the number I used from the beginning, the preview monitor works correctly. If I keep it at the default 6 fps in the preview setting, everything speeds way up. But the other problem is that if I set the fps to 24 instead of 12, everything slows down four times as slow… So maybe the whole problem is the preview monitor.