I know it's been a few months since the last post in this thread, but I think I (kinda) know why retroarch wii has audio stuttering and lags ever since 1.5.0.
I've been having the same problem for a while now, ever since I tried to make my Wii into an emulation system. When I fist downloaded retroarch wii, it lagged and stuttered, so I tried to get to the root of the problem. I changed all of the video and audio settings but it didn't solve anything, so I gave up. Recently I decided to try again but once again I had no luck. Searching on the internet I found this thread which confirmed that I wasn't the only one who was having issues with this, however also found proof that not everyone had this problem. So thinking about it I started to wonder whether this had something to do with the fact that I have a PAL Wii but use NTSC roms for emulation, as in the retroarch settings the screen refresh rate was stuck at 50Hz every time I restarted retroarch. I also saw that enabling threaded video while the content was running (not before as it would cause retroarch to crash upon loading a rom) would help with tgis issue but would also cause it to crash at times as threaded video implementation on retroarch wii is unstable. I knew threaded video also had something to do with the refresh rate, so my suspicions increased.
To confirm my suspicions I loaded the Snes9x core on retroarch 1.7.1 (stable build) and loaded my only PAL SNES rom: Parodius - Non Sense Fantasy, which only came out in Japan and Europe. And, sure enough, it worked perfectly; no audio stuttering or slowdown. So I proceeded to change the settings of my wii under the option "TV Type" to 60Hz (480i). This caused it all to be slightly blurrier an some artifacts (such as the letters in the retroarch menu having some blue and yellow flashes sometimes) and also caused retroarch with the resolution set to 640x480 to be slightly cut off vertically in my TV (although this may be due to my tv being PAL). However it also made retroarch run perfectly.
From my experiments with the display fps setting ebabled in retroarch, I think that retroarch detects the mode your Wii is running in and caps the framerate at that. So if you have a Wii running in PAL 50Hz mode, the framerate will be capped at 50 fps which will make NTSC games which run at 60 fps unplayable but PAL games which run at 50 fps will run perfectly.
So to solve your issue, CoolKill3r, and supposing your wii is in PAL 50Hz (576i) mode, try changing it to NTSC 60Hz (480i). This is by no means a permanent solution, as we know from retroarch wii 1.5.x that retroarch can run perfectly independently of your Wii's settings. So the questions here are: Can this be reverted to how it worked in retroarch wii 1.5.x? Am I doing something wrong? Will this ever be fixed?
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By the way, I don't have the component cables so I haven't tried the EDTV/HDTV (480p) mode