No
http://192.168.1.xxx/onvifsnapshot/media_service/snapshot?channel=3&subtype=0?
everything after
http://192.168.1.xxx/onvifsnapshot/...
works with channel 1, I've tried up to channel 8, even
http://192.168.1.xxx/onvifsnapshot/trallala
and
http://192.168.1.xxx/onvifsnapshot/
work with channel 1...