Odd video size and rates - RPI

[steeley]

Sending from a Logitech c270 USB cam plugged into Raspberry Pi 4 running Buster.

Only 640x480 15fps works well , also 1280 x 720 but at 2fps although camera should do 15fps

ffmpeg on OSX reports rather odd formats supported:

[avfoundation @ 0x7fcbeb831400] Selected framerate (29.970030) is not supported by the device.
[avfoundation @ 0x7fcbeb831400] Supported modes:
[avfoundation @ 0x7fcbeb831400]   640x360@[15.000015 15.000015]fps
[avfoundation @ 0x7fcbeb831400]   640x360@[10.000000 10.000000]fps  
[avfoundation @ 0x7fcbeb831400]   640x360@[2.000000 2.000000]fps
[avfoundation @ 0x7fcbeb831400]   1280x720@[2.000000 2.000000]fps
[avfoundation @ 0x7fcbeb831400]   640x360@[15.000015 15.000015]fps
[avfoundation @ 0x7fcbeb831400]   640x360@[10.000000 10.000000]fps
[avfoundation @ 0x7fcbeb831400]   640x360@[2.000000 2.000000]fps
[avfoundation @ 0x7fcbeb831400]   1280x720@[2.000000 2.000000]fps