Make it work

[yuripourre]

Successfully define format but can't send frames (probably because jcharArray and (C/C++)char[] differ on size)

jboolean isCopy;
    jbyte* a = env->GetByteArrayElements(bArray, &isCopy);
    char* b;
    b = (char*)a;

https://codeday.me/en/qa/20190306/6130.html
https://stackoverflow.com/a/8439341

Init cameras

sudo modprobe v4l2loopback devices=2 exclusive_caps=1,1

Common issues

https://github.com/umlaeute/v4l2loopback/issues/78
https://github.com/umlaeute/v4l2loopback/issues/134

Bypass /dev/video0 to /dev/video3:

gst-launch-1.0 v4l2src device=/dev/video0 ! videorate ! v4l2sink device=/dev/video3

Check format with ffmpeg:

ffmpeg -f v4l2 -list_formats all -i /dev/video3