<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Appendix D. Video Grabber example using libv4l</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API" /><link rel="up" href="pt01.html" title="Part I. Video for Linux Two API Specification" /><link rel="prev" href="apc.html" title="Appendix C. Video Capture Example" /><link rel="next" href="ix01.html" title="List of Types" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Appendix D. Video Grabber example using libv4l</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="apc.html">Prev</a> </td><th width="60%" align="center">Part I. Video for Linux Two API Specification</th><td width="20%" align="right"> <a accesskey="n" href="ix01.html">Next</a></td></tr></table><hr /></div><div class="appendix" title="Appendix D. Video Grabber example using libv4l"><div class="titlepage"><div><div><h2 class="title"><a id="v4l2grab-example"></a>Appendix D. Video Grabber example using libv4l</h2></div></div></div><p>This program demonstrates how to grab V4L2 images in ppm format by using libv4l handlers. The advantage is that this grabber can potentially work with any V4L2 driver.</p><pre class="programlisting"> /* V4L2 video picture grabber Copyright (C) 2009 Mauro Carvalho Chehab <mchehab@infradead.org> This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation version 2 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. */ #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 "../libv4l/include/libv4l2.h" #define CLEAR(x) memset(&(x), 0, sizeof(x)) struct buffer { void *start; size_t length; }; static void xioctl(int fh, int request, void *arg) { int r; do { r = v4l2_ioctl(fh, request, arg); } while (r == -1 && ((errno == EINTR) || (errno == EAGAIN))); if (r == -1) { fprintf(stderr, "error %d, %s\n", errno, strerror(errno)); exit(EXIT_FAILURE); } } int main(int argc, char **argv) { struct <a class="link" href="re41.html#v4l2-format" title="Table A.46. struct v4l2_format">v4l2_format</a> fmt; struct <a class="link" href="ch03s05.html#v4l2-buffer" title="Table 3.1. struct v4l2_buffer">v4l2_buffer</a> buf; struct <a class="link" href="re59.html#v4l2-requestbuffers" title="Table A.72. struct v4l2_requestbuffers">v4l2_requestbuffers</a> req; enum <a class="link" href="ch03s05.html#v4l2-buf-type" title="Table 3.2. enum v4l2_buf_type">v4l2_buf_type</a> type; fd_set fds; struct timeval tv; int r, fd = -1; unsigned int i, n_buffers; char *dev_name = "/dev/video0"; char out_name[256]; FILE *fout; struct buffer *buffers; fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0); if (fd < 0) { perror("Cannot open device"); exit(EXIT_FAILURE); } CLEAR(fmt); fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; fmt.fmt.pix.width = 640; fmt.fmt.pix.height = 480; fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24; fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; xioctl(fd, VIDIOC_S_FMT, &fmt); if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) { printf("Libv4l didn't accept RGB24 format. Can't proceed.\n"); exit(EXIT_FAILURE); } if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480)) printf("Warning: driver is sending image at %dx%d\n", fmt.fmt.pix.width, fmt.fmt.pix.height); CLEAR(req); req.count = 2; req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; req.memory = V4L2_MEMORY_MMAP; xioctl(fd, VIDIOC_REQBUFS, &req); buffers = calloc(req.count, sizeof(*buffers)); for (n_buffers = 0; n_buffers < req.count; ++n_buffers) { CLEAR(buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = n_buffers; xioctl(fd, VIDIOC_QUERYBUF, &buf); buffers[n_buffers].length = buf.length; buffers[n_buffers].start = v4l2_mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset); if (MAP_FAILED == buffers[n_buffers].start) { perror("mmap"); exit(EXIT_FAILURE); } } for (i = 0; i < n_buffers; ++i) { CLEAR(buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = i; xioctl(fd, VIDIOC_QBUF, &buf); } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; xioctl(fd, VIDIOC_STREAMON, &type); for (i = 0; i < 20; i++) { do { FD_ZERO(&fds); FD_SET(fd, &fds); /* Timeout. */ tv.tv_sec = 2; tv.tv_usec = 0; r = select(fd + 1, &fds, NULL, NULL, &tv); } while ((r == -1 && (errno = EINTR))); if (r == -1) { perror("select"); return errno; } CLEAR(buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; xioctl(fd, VIDIOC_DQBUF, &buf); sprintf(out_name, "out%03d.ppm", i); fout = fopen(out_name, "w"); if (!fout) { perror("Cannot open image"); exit(EXIT_FAILURE); } fprintf(fout, "P6\n%d %d 255\n", fmt.fmt.pix.width, fmt.fmt.pix.height); fwrite(buffers[buf.index].start, buf.bytesused, 1, fout); fclose(fout); xioctl(fd, VIDIOC_QBUF, &buf); } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; xioctl(fd, VIDIOC_STREAMOFF, &type); for (i = 0; i < n_buffers; ++i) v4l2_munmap(buffers[i].start, buffers[i].length); v4l2_close(fd); return 0; } </pre></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="apc.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="pt01.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ix01.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Appendix C. Video Capture Example </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> List of Types</td></tr></table></div></body></html>