v4l2

I have written an application which reads from a webcam and processes the frames using OpenCV on linux. Now I want to pipe the output of my application to a virtual webcam that has been created by the V4L2loopback module so other applications are able to read it. I have written the application using C. I am not sure how to approach doing this. Could you please give me any hints? user477519 I have found an answer in the old V4L2loopback module's page on Google code. http://code.google.com/p/v4l2loopback/source/browse/test.c newer link: https://github.com/umlaeute/v4l2loopback/blob/master

I'm looking for a simple example for camera access in Linux using V4L2. Where I can find it? As simple, as possible. Thanks, Raulp Try the uvccapture code here -> http://staticwave.ca/source/uvccapture/ It is very small yet very concrete example which makes use of all the V4l2 concepts (open,set format, allocate memory, Request Buffer, Dqbuffer and Query-buffer - all intems of ioclts). uvcgrab () function is the one to look for which makes use of Dqbuffer and Query-buffer. ioctl (vd->fd, VIDIOC_DQBUF, &vd->buf); ioctl (vd->fd, VIDIOC_QBUF, &vd->buf) While Studying it you can keep looking for

In a native call, I'm trying to open("/dev/video4", O_RDWR) but I get errno EACCES 13 "permission denied". If I run the same code* in an executable, on the same Android host, as the same UID of the installed app I'm running above, it works fine. (* minor differences like main() instead of Java_com_test_testOpen() ) I've tried chmod 666 /dev/video4 and still get EACCES, which is especially strange. Why does the same code , on the same host , as the same user , give EACCESS when called via JNI, and success when called as standalone executable? The test device is rooted and running Cyanogenmod 12

I'm trying to capture H264 stream from locally installed Logitech C920 camera from /dev/video0 with Gstreamer 1.0 v4l2src element. v4l2-ctl --list-formats shows that camera is capable to give H264 video format: # v4l2-ctl --list-formats ioctl: VIDIOC_ENUM_FMT ... Index : 1 Type : Video Capture Pixel Format: 'H264' (compressed) Name : H.264 ... But pipeline # gst-launch-1.0 -vvv v4l2src device=/dev/video0 ! video/x-h264, width=800, height=448, framerate=30/1 ! fakesink keeps giving me not-negotiated (-4) error: /GstPipeline:pipeline0/GstV4l2Src:v4l2src0.GstPad:src: caps = video/x-h264, width=

在取出一帧数据的时候，我使用的是以下的代码： struct v4l2_buffer buf; memset(&buf, 0, sizeof(buf)); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if(ioctl(fd, VIDIOC_DQBUF, &buf) == -1) { printf("VIDIOC_DQBUF failed\n"); return -10; } printf("VIDIOC_DQBUF success\n"); 运行的结果是ioctl一直返回-1，一直无法解决这个问题 但当我在这一步之前加上select进行检测，就解决了这个问题 fd_set fds; struct timeval tv; FD_ZERO(&fds); FD_SET(fd, &fds); tv.tv_sec = 2; tv.tv_usec = 0; int ret; ret = select(fd+1, &fds, NULL, NULL, &tv); 这以上代码中设置时延来检测fd是否有数据，当fd有数据的时候，select才会返回，不然select会阻塞在那里等待； 这样子就解决了之前的问题，之前的问题是当开始启动摄像头获取数据的时候，马上使用ioctl获取一帧的数据