Hi all, I can avoid the known parsing error "Window size specification out of bounds!" by entering x, y, and width. So I can capture video and JACK-sound with
recordmydesktop --channels 2 --use-jack system:capture_1 system:capture_2 -x 0 -y 0 --width 1920 --height 1200
But it only records one channel, not both. In the recorded ogv-file only the left channel has a signal.