About MacOS 9 retro-gaming on modern flat screens with video capture and VSYNC

[Aliotech1]

Hello everyone!

After doing a lot of research, I'm happy to share my knowledge with you so you don't make the same mistakes I did if you want to capture sound and video from an old Mac or just display it on a modern screen in a quality way.

Some tips in bulk:
- I would not recommend the Elgato HD60 S+ or Avermedia Live Gamer Ultra frame grabbers. These cards are unable to capture the signal of old Macs properly. Find yourself a new or used Magewell HDMI card that is able to accept all resolutions with many frequencies without worry.
- I would not recommend using an HDMI/DVI adapter on the mac mini. The picture quality will be better than with VGA, but you won't be able to include the sound in the HDMI signal and thus choose between recording it or listening to it with a speaker set. Instead, I strongly advise you to use an OSSC (Open Source Scan Converter) to which you connect your Mac in VGA. The OSSC has a jack port to digitize the sound of your Mac and include it in the HDMI signal in good quality.
- I recommend Magewell's HDMI capture cards. The VGA-compatible DVI card does not work well with older Macs, so I do not recommend it.
- I advise you to use the 85 Hz refresh rate. After many tests, this is a refresh rate that gives a very good result on Mac OS 9: games will hardly have any image tearing, it's almost perfect and the visual experience will be much more pleasant than in 60 Hz. If your screen does not support it, you will have to stay in 60 Hz. Some games especially under Mac OS X will tend to slow down a lot in 85 Hz, and the only way to have a smooth experience in this case is to switch back to 60 Hz. Whenever possible, play games in 85 Hz.
- I advise you to use SwitchRes to disallow all the resolutions you don't want, so that a game can't force the reconfiguration of your screen

I did all the configuration with a Mac Mini G4. Then, I tested with iBook G3 connected in VGA on the OSSC : the OSSC must be reconfigured for 800x600 and 1024x768 resolutions, but I could keep a common 640x480@85Hz configuration between my 2 macs.

Here are the settings I use on my OSSC and that work perfectly with my Mac Mini 1.42GHz, I spent a lot of time to find them and I hope they will be useful for you :
640x480@60Hz
H. samplerate : 800
H. s.rate frac : .00
H. synclen : 96
H. backporch : 55
H. active : 640
V. synclen : 2
V. backporch : 41
V. active : 480
Sampling phase : 180 deg

640x480@85Hz
H. samplerate : 832
H. s.rate frac : .00
H. synclen : 60
H. backporch : 75
H. active : 640
V. synclen : 1
V. backporch : 27
V. active : 480
Sampling phase : 168 deg

800x600@85Hz
H. samplerate : 1048
H. s.rate frac : .00
H. synclen : 87
H. backporch : 124
H. active : 800
V. synclen : 4
V. backporch : 26
V. active : 600
Sampling phase : 180 deg

1024x768@85Hz
H. samplerate : 1376
H. s.rate frac : .00
H. synclen : 152
H. backporch : 149
H. active : 1024
V. synclen : 3
V. backporch : 36
V. active : 768
Sampling phase : 180 deg

I put some screenshots that were made directly from the capture using OBS.
To sum up, my chain is :

For Audio :
Audio Jack coming from the Mac Mini ==> OSSC AV3 IN (the OSSC will include the audio directly on the HDMI signal)

For Video :
VGA cable plugged from the Mac Mini to the OSSC AV3 IN.
Then the HDMI OUT port of the OSSC is linked with the Magewell HDMI Capture Card (which has HDMI passthrough, so you can use another HDMI cable to plug it on a screen and play with minimal latency while capturing).