twam / v4l2grab

utility for grabbing JPEGs from V4L2 devices

v4l2grab

This is a small command line utility for grabbing JPEGs form V4L2 devices (e.g. USB webcams).

For installation, follow the instructions into the GitHub Wiki.

Try ./v4l2grab -h or just v4l2grab if you have installed it to get some help.

If your webcam works, please add it to the Compatible Devices table.

v4l2grab's Issues

make[1]: Leaving directory `/root/v4l2grab'

When running make, i get the following error;

root@beaglebone:~/v4l2grab# make
make all-am
make[1]: Entering directory /root/v4l2grab' gcc -DHAVE_CONFIG_H -I. -g -O2 -MT v4l2grab.o -MD -MP -MF .deps/v4l2grab.Tpo -c -o v4l2grab.o v4l2grab.c mv -f .deps/v4l2grab.Tpo .deps/v4l2grab.Po gcc -DHAVE_CONFIG_H -I. -g -O2 -MT yuv.o -MD -MP -MF .deps/yuv.Tpo -c -o yuv.o yuv.c mv -f .deps/yuv.Tpo .deps/yuv.Po gcc -g -O2 -o v4l2grab v4l2grab.o yuv.o -lv4l2 -ljpeg make[1]: Leaving directory/root/v4l2grab'

I am installing it on BeagleBone Black Rev C running Debian Wheezy, 3.8.13-bone79.

YUVtoRGB-conversion unnecessary

Since JPEG stores data in the YCbCr-Colorspace [http://en.wikipedia.org/wiki/JFIF#Color_space], the conversion from YUVxyz to RGB is unnecessary. libjpeg(-turbo) is capable of storing YUV444 (JCS_YCbCr). This still requires conversion from most v4l2-devices, but mostly only from YUVxyz to YUV444 which is a lot less computationally intensive than YUV to RGB.

Interval option has random results.

When trying to use the interval option, I'm getting some odd results. Interval of 1 or 2 works fine. However, with interval 3:

v4l2grab -q 100 -W 2592 -H 1944 --interval 3 -c -o test

It only takes 2 images every second, not three. If I then change interval to 4 or higher, it just takes the maximum images per second it can (between 5 and 6 for max resolution, higher if I set the resolution lower).

Any ideas what's going on? I need to set the interval to 4 if possible (I know it won't be exact, but I need approximately 4 images per second).

Buffer size larger than required

Why ist v4l2grab using a 4 stage buffer (req.count = 4) if it actually just writes one picture into a jpeg file?

compilation error, YUV420toYUV444 function is missing

compilation error:

$ gcc v4l2grab.c -o v4l2grab -Wall -ljpeg -lv4l2 -DIO_READ -DIO_MMAP -DIO_USERPTR

/tmp/user/1000/ccIvliiI.o: In function `imageProcess':
v4l2grab.c:(.text+0x374): undefined reference to `YUV420toYUV444'
collect2: error: ld returned 1 exit status

Having gcc v7.3 and following v4l packages installed:

$ apt list --installed | grep v4l

libv4l-0/bionic,now 1.14.2-1 amd64 [installed]
libv4l-dev/bionic,now 1.14.2-1 amd64 [installed]
libv4l2rds0/bionic,now 1.14.2-1 amd64 [installed]
libv4lconvert0/bionic,now 1.14.2-1 amd64 [installed]
v4l-conf/bionic,now 3.103-4build1 amd64 [installed]
v4l-utils/bionic,now 1.14.2-1 amd64 [installed]
v4l2loopback-dkms/bionic,bionic,now 0.10.0-1ubuntu1 all [installed]
v4l2loopback-source/bionic,bionic,now 0.10.0-1ubuntu1 all [installed]
v4l2loopback-utils/bionic,now 0.10.0-1ubuntu1 amd64 [installed]
v4l2ucp/bionic,now 2.0.2-4build1 amd64 [installed]