The exact same thing happened to me when I played Spyro 2: Season of Flame.

Very latest version of mGBA, Windows 7, GTX 970, i5.

Have you confirmed it's not just the FPS counter, but that the FPS itself is actually dropping?

Have you confirmed it's not just the FPS counter, but that the FPS itself is actually dropping?

Hi endrift

Yes, I confirm the FPS is actually drop together with the sound

I haven't been able to reproduce this yet; I've left Mother 3 on audio test for about 5 hours to no framerate reduction.

Hi Endrift

the issue persisting, anyway, I can always close and reopen. it may be the compatibility issue with graphic driver or audio driver.

I tried to switch the display driver to the software(Qt) driver, the FPS drop to 0.5FPS (unplayable). but the CPU usage is only 3%

The software driver slows down if the window is larger. Are you in full screen?

Yes, I'm using full screen and the screen resolution is 4k

Do you think the issue related to this full screen 4k resolution? I will try the smaller window and report it back
Thanks

That explains why the software driver is so slow. See if a smaller window (1x preferable) makes software work at a reasonable rate and still slow down over time.

If it does still slow down over time try fiddling with the audio driver settings.

That explains why the software driver is so slow. See if a smaller window (1x preferable) makes software work at a reasonable rate and still slow down over time.
If it does still slow down over time try fiddling with the audio driver settings.

Hi endrift

I tried to use x1 with software driver, the FPS locked at 0.5FPS with CPU load at 2% (unplayable)
I tried the x1 mode with OpenGL driver, it still slows down after a while.

the game I tested is final fantasy VI advance.

Thanks

What are your sync settings, i.e. Sync to audio (recommended), sync to video, or both (not recommended)?

I used to set sync to both
after I read your comment, I did below test
first, only turn off sync to video, game still slows down
then, turn off both sync, FPS goes to 600
finally, only turn off sync to audio, game no longer slows down

seems the issue is related to the audio driver

I'm using a usb audio interface (Focusrite Scarlett 2i4) ASIO audio driver with sample rate 48khz, buffer 256

I think I solved the issue

if I choose buffer size 512 in my audio interface control panel, then the game no longer slows down

Thanks

@kurayami6 can you confirm if this also fixes it for you?

Yeah it's fixed.