How to get the video from webcam using v4l2 linux interface?

Question

I am trying to run the sample code from v4l2 API. When I tried to run the sample code, I am facing problem while compiling the program itself. Please check the error, is there something I need to install or flag to pass during the compilation steps?

ubox:~/capVideoFrame$ gcc v4l2grab.c && ./a.out
/tmp/cc0E2uRM.o: In function `xioctl':
v4l2grab.c:(.text+0x2b): undefined reference to `v4l2_ioctl'
/tmp/cc0E2uRM.o: In function `main':
v4l2grab.c:(.text+0xf3): undefined reference to `v4l2_open'
v4l2grab.c:(.text+0x30f): undefined reference to `v4l2_mmap'
v4l2grab.c:(.text+0x6a2): undefined reference to `v4l2_munmap'
v4l2grab.c:(.text+0x6c4): undefined reference to `v4l2_close'
collect2: error: ld returned 1 exit status

Source code header file:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include "/usr/include/libv4l2.h" // I am using ubuntu, so pointing to this location

No luck, `gcc -lv4l1 -lv4l2 v4l2grab.c` - same error – ajayramesh Mar 09 '18 at 21:09 — ajayramesh, Mar 09 '18 at 21:09
worked! please write it as answer – ajayramesh Mar 09 '18 at 21:22 — ajayramesh, Mar 09 '18 at 21:22

score 2 · Accepted Answer · answered Mar 09 '18 at 21:23

2

To successfully compiled you need add flags for it -lv4l1 -lv4l2

gcc v4l2grab.c -lv4l1 -lv4l2

answered Mar 09 '18 at 21:23

Nick S

1,299
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23

why we need those flags ? – ajayramesh Mar 09 '18 at 21:30
1

It "link" your program with necessary v4l2 libraries – Nick S Mar 09 '18 at 21:31
2

Please read this article https://www.lurklurk.org/linkers/linkers.html it will be much clearer why all this is required. – Mar 09 '18 at 21:32

score 0 · Answer 2 · answered Nov 01 '20 at 10:43

0

In case you didn't install libv4l2 before, you need to install it first:

sudo apt-get install -y libv4l-dev

BTW, the above link is dead, the new link is here.

answered Nov 01 '20 at 10:43

Le Dinh-Tuyen

1

Welcome to SO. I think the OP had already installed the library and the issue was not including the right flags. – ewokx Nov 02 '20 at 01:24

How to get the video from webcam using v4l2 linux interface?

2 Answers2