Dear Kaczorek,
I just wonder, whether something like a "video buffer" in memory could be used in the pi4 (esp. the 4GB version) to speed up captured frame rates of cams connected via USB3. With my cam (QHY 5III178) I just get framerates around 4 fps in full resolution. Even with my old toucam I just see 10 fps. I assume the bottleneck is in storing the data on the SD ? So if 1 to 3 GB could be reserved as a video buffer in memory, the camera could record with the maximum speed of the USB3 until the buffer is filled, than the buffer would be piped onto the SD while capture is being paused. Does this sound feasable ?
Thanks and kind regards
Dirk

Your new camera has 3 times the resolution of the old, which would explain the lower framerate.

You could create a RAM drive and save the video to there, before copying to the SD card. Either that or try getting a high speed USB3 memory stick such as the SanDisk Extreme models and save to that.

www.domoticz.com/wiki/Setting_up_a_RAM_drive_on_Raspberry_Pi

Thanks - I realised only later that the low fps I was seeing could not be related to the data storage as I was having low frame rates without recording.
I did experiment with the usb speed setting, and quite counterintuitively I have to set it lower to get better frame rates. In full frame, a value around 20 gives best results (around 8-10 fps in 16bit mono). When I set a lower RoI (e.g. 500x500) I see frame rates up to 60 fps when setting the USB speed to single digits. Then I did indeed ran into problems with recording speed, which dropped every couple of seconds. I solved this through attaching a USB SSD. Btw, all of this data is from using oacapture.