There seems to be only one way to feed live video from Boscam HD19 FPV camera to Raspberry Pi over wire. To do that you’ll need composite AV to USB capture card. The one I had lying around is called KWorld VS-USB2800D Composite/S-Video to USB 2.0 (see Pic 1 and 2).
Connect Boscam camera to capture card with supplied mini USB to composite AV cable. Insert supplied multifunctional port’s power cable and connect it to 12 V battery (as per Boscam’s specification). I used Turnigy 3S 11.1 V battery which seems to do the job. See pics bellow.
Connect capture card to Raspberry’s USB port (Pic 6).
Turn on your Boscam camera by holding its power button and start Raspberry. If you’re lucky Raspberry will detect your capture card on boot and it’ll be ready to use. You can quickly test it with software like guvcview. You can find an incomplete list of supported devices here.
In my case, even though everything was detected, all I got was black screen. The problem was that KWorld’s capture card has two inputs: S-Video and composite and it defaults to using S-Video.
To fix this I listed available channels:
and selected composite channel: