On UVC devices with a metadata node, 'capabilities' describes the whole physical device, so /dev/video1 (metadata) also advertised VIDEO_CAPTURE and won the highest-numbered pick — then S_FMT failed forever and cap reported no cameras on a working built-in webcam (ThinkPad 04f2:b6d9). Use device_caps when V4L2_CAP_DEVICE_CAPS is set.