Why this warning

stark@Shashivardhan:~/yolo-9000/darknet$ ./darknet detector demo cfg/combine9k.data cfg/yolo9000.cfg …/yolo9000-weights/yolo9000.weights -c 0 -t 5000
Demo
layer filters size input output
0 conv 32 3 x 3 / 1 544 x 544 x 3 → 544 x 544 x 32 0.511 BFLOPs
1 max 2 x 2 / 2 544 x 544 x 32 → 272 x 272 x 32
2 conv 64 3 x 3 / 1 272 x 272 x 32 → 272 x 272 x 64 2.727 BFLOPs
3 max 2 x 2 / 2 272 x 272 x 64 → 136 x 136 x 64
4 conv 128 3 x 3 / 1 136 x 136 x 64 → 136 x 136 x 128 2.727 BFLOPs
5 conv 64 1 x 1 / 1 136 x 136 x 128 → 136 x 136 x 64 0.303 BFLOPs
6 conv 128 3 x 3 / 1 136 x 136 x 64 → 136 x 136 x 128 2.727 BFLOPs
7 max 2 x 2 / 2 136 x 136 x 128 → 68 x 68 x 128
8 conv 256 3 x 3 / 1 68 x 68 x 128 → 68 x 68 x 256 2.727 BFLOPs
9 conv 128 1 x 1 / 1 68 x 68 x 256 → 68 x 68 x 128 0.303 BFLOPs
10 conv 256 3 x 3 / 1 68 x 68 x 128 → 68 x 68 x 256 2.727 BFLOPs
11 max 2 x 2 / 2 68 x 68 x 256 → 34 x 34 x 256
12 conv 512 3 x 3 / 1 34 x 34 x 256 → 34 x 34 x 512 2.727 BFLOPs
13 conv 256 1 x 1 / 1 34 x 34 x 512 → 34 x 34 x 256 0.303 BFLOPs
14 conv 512 3 x 3 / 1 34 x 34 x 256 → 34 x 34 x 512 2.727 BFLOPs
15 conv 256 1 x 1 / 1 34 x 34 x 512 → 34 x 34 x 256 0.303 BFLOPs
16 conv 512 3 x 3 / 1 34 x 34 x 256 → 34 x 34 x 512 2.727 BFLOPs
17 max 2 x 2 / 2 34 x 34 x 512 → 17 x 17 x 512
18 conv 1024 3 x 3 / 1 17 x 17 x 512 → 17 x 17 x1024 2.727 BFLOPs
19 conv 512 1 x 1 / 1 17 x 17 x1024 → 17 x 17 x 512 0.303 BFLOPs
20 conv 1024 3 x 3 / 1 17 x 17 x 512 → 17 x 17 x1024 2.727 BFLOPs
21 conv 512 1 x 1 / 1 17 x 17 x1024 → 17 x 17 x 512 0.303 BFLOPs
22 conv 1024 3 x 3 / 1 17 x 17 x 512 → 17 x 17 x1024 2.727 BFLOPs
23 conv 28269 1 x 1 / 1 17 x 17 x1024 → 17 x 17 x28269 16.732 BFLOPs
24 detection
mask_scale: Using default ‘1.000000’
Loading weights from …/yolo9000-weights/yolo9000.weights…Done!
video file: -t
[ WARN:0@19.996] global cap.cpp:204 open VIDEOIO(V4L2): backend is generally available but can’t be used to capture by name
Couldn’t connect to webcam.
: No such file or directory
darknet: ./src/utils.c:256: error: Assertion `0’ failed.
Aborted
why this warning