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本篇内容介绍了“USB摄像头linux实现方法是什么”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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做嵌入式linux上的开发很多年了，扳手指头算算，也起码9年了，陆陆续续做过很过诸如需要读取外接的USB摄像头或者CMOS摄像机的程序，实时采集视频，将图像传到前端，或者对图像进行人脸分析处理，最开始尝试的就是QCamera来处理，直接歇菜放弃，后面通过搜索发现都说要用v4l2视频框架来进行，于是东搞搞西搞搞尝试了很多次，终于整出来了，前后完善了好几年，无论写什么程序，发现要简简单单的实现基础的功能，都是非常快速而且容易的，但是想要做得好做得精，要花不少的精力时间去完善，适应各种不同的场景，比如就说用v4l2加载摄像头这个，需要指定设备文件来读取，而现场不可能让用户来给你指定，频繁的拔插也会导致设备文件名的改动，所以必须找到一个机制自动寻找你想要的摄像机的设备文件名称，比如开个定时器去调用linux命令来处理，甚至在不同的系统平台上要执行的命令还有些许的区别，如果本地有多个摄像头还需要区分左右之类的时候，那就只能通过断电先后上电顺序次序来区分了。
linux方案处理流程：
调用封装的函数findCamera实时查找摄像头设备文件名。
调用::open函数打开设备文件。
调用封装的函数initCamera初始化摄像头参数（图片格式、分辨率等）。
调用::select函数从缓冲区取出一个缓冲帧。
缓冲帧数据是yuyv格式的，需要转换rgb24再转成QImage。
拿到图片进行绘制、人脸分析等。
关闭设备文件。
同时支持windows、linux、嵌入式linux上的USB摄像头实时采集。
支持多路USB摄像头多线程实时采集。
在嵌入式linux设备上，自动查找USB设备文件并加载。
可手动设置设备文件名称，手动设置后按照手动设置的设备文件加载。
在嵌入式linux设备上支持人脸识别接口，实时绘制人脸框。
具有打开、暂停、继续、关闭、截图等常规功能。
可设置两路OSD标签，分别设置文本、颜色、字号、位置等。
可作为视频监控系统使用。
void CameraLinux::run()
{
while (!stopped) {
if (!cameraOk) {
msleep(10);
continue;
}
if (isPause) {
//这里需要假设正常,暂停期间继续更新时间
lastTime = QDateTime::currentDateTime();
msleep(10);
continue;
}
QImage image = readImage();
if (!image.isNull()) {
if (isSnap) {
emit snapImage(image);
isSnap = false;
}
if (findFaceOne) {
findFace(image);
}
if (findFaceRect) {
image = drawFace(image);
}
lastTime = QDateTime::currentDateTime();
emit receiveImage(image);
}
msleep(interval);
}
this->closeCamera();
this->initData();
}
QDateTime CameraLinux::getLastTime() const
{
return this->lastTime;
}
QString CameraLinux::getCameraName() const
{
return this->cameraName;
}
int CameraLinux::getCameraWidth() const
{
return this->cameraWidth;
}
int CameraLinux::getCameraHeight() const
{
return this->cameraHeight;
}
void CameraLinux::sleep(int msec)
{
if (msec > 0) {
QTime endTime = QTime::currentTime().addMSecs(msec);
while (QTime::currentTime() < endTime) {
QCoreApplication::processEvents(QEventLoop::AllEvents, 100);
}
}
}
void CameraLinux::initData()
{
stopped = false;
isPause = false;
isSnap = false;
cameraOk = false;
cameraHwnd = -1;
errorCount = 0;
}
void CameraLinux::readData()
{
QStringList cameraNames;
while (!process->atEnd()) {
//逐行读取返回的结果 过滤video开头的是摄像头设备文件
QString line = process->readLine();
if (line.startsWith("video")) {
line = line.replace("\n", "");
cameraNames << QString("/dev/%1").arg(line);
}
}
if (cameraNames.count() > 0) {
cameraName = cameraNames.first();
emit receiveCamera(cameraNames);
qDebug() << TIMEMS << cameraNames;
}
}
bool CameraLinux::initCamera()
{
//如果没有指定设备文件名称(默认auto)则查找
if (cameraName == "auto") {
findCamera();
}
//延时判断是否获取到了设备文件
sleep(300);
return openCamera();
}
void CameraLinux::findCamera()
{
if (process->state() == QProcess::NotRunning) {
process->start("ls /dev/");
}
}
bool CameraLinux::openCamera()
{
#ifdef Q_OS_LINUX
if (cameraName.length() > 5) {
cameraHwnd = ::open(cameraName.toUtf8().data(), O_RDWR | O_NONBLOCK, 0);
}
if (cameraHwnd < 0) {
qDebug() << TIMEMS << "open camera error";
return false;
}
//查询设备属性
struct v4l2_capability capability;
if (::ioctl(cameraHwnd, VIDIOC_QUERYCAP, &capability) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_QUERYCAP";
::close(cameraHwnd);
return false;
}
if (!(capability.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
qDebug() << TIMEMS << "it is not a video capture device";
::close(cameraHwnd);
return false;
}
if (!(capability.capabilities & V4L2_CAP_STREAMING)) {
qDebug() << TIMEMS << "it can not streaming";
::close(cameraHwnd);
return false;
}
if (capability.capabilities == 0x4000001) {
qDebug() << TIMEMS << "capabilities" << "V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING";
}
//设置视频输入源
int input = 0;
if (::ioctl(cameraHwnd, VIDIOC_S_INPUT, &input) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_S_INPUT";
::close(cameraHwnd);
return false;
}
//设置图片格式和分辨率
struct v4l2_format format;
format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
//多种格式 V4L2_PIX_FMT_YUV420 V4L2_PIX_FMT_YUYV(422) V4L2_PIX_FMT_RGB565
format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
//部分硬件花屏要设置成 V4L2_FIELD_NONE
format.fmt.pix.field = V4L2_FIELD_INTERLACED;
format.fmt.pix.width = cameraWidth;
format.fmt.pix.height = cameraHeight;
int bpp = 16;
//format.fmt.pix.bytesperline = width * bpp / 8;
//format.fmt.pix.sizeimage = cameraWidth * cameraHeight * bpp / 8;
if (::ioctl(cameraHwnd, VIDIOC_S_FMT, &format) < 0) {
::close(cameraHwnd);
return false;
}
//查看图片格式和分辨率,判断是否设置成功
if (::ioctl(cameraHwnd, VIDIOC_G_FMT, &format) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_G_FMT";
::close(cameraHwnd);
return false;
}
//重新打印下宽高看下是否真正设置成功
struct v4l2_pix_format pix = format.fmt.pix;
quint32 pixelformat = pix.pixelformat;
qDebug() << TIMEMS << "cameraWidth" << cameraWidth << "cameraHeight" << cameraHeight << "width" << pix.width << "height" << pix.height;
qDebug() << TIMEMS << "pixelformat" << QString("%1%2%3%4").arg(QChar(pixelformat & 0xFF)).arg(QChar((pixelformat >> 8) & 0xFF)).arg(QChar((pixelformat >> 16) & 0xFF)).arg(QChar((pixelformat >> 24) & 0xFF));
//重新设置宽高为真实的宽高
cameraWidth = pix.width;
cameraHeight = pix.height;
//设置帧格式
struct v4l2_streamparm streamparm;
streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
streamparm.parm.capture.timeperframe.numerator = 1;
streamparm.parm.capture.timeperframe.denominator = 25;
streamparm.parm.capture.capturemode = 0;
if (::ioctl(cameraHwnd, VIDIOC_S_PARM, &streamparm) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_S_PARM";
::close(cameraHwnd);
return false;
}
if (::ioctl(cameraHwnd, VIDIOC_G_PARM, &streamparm) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_G_PARM";
::close(cameraHwnd);
return false;
}
//申请和管理缓冲区
struct v4l2_requestbuffers requestbuffers;
requestbuffers.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
requestbuffers.memory = V4L2_MEMORY_MMAP;
requestbuffers.count = 1;
if (::ioctl(cameraHwnd, VIDIOC_REQBUFS, &requestbuffers) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_REQBUFS";
::close(cameraHwnd);
return false;
}
buff_yuv422 = (uchar *)malloc(cameraWidth * cameraHeight * bpp / 8);
buff_yuv420 = (uchar *)malloc(cameraWidth * cameraHeight * bpp / 8);
buff_rgb24 = (uchar *)malloc(cameraWidth * cameraHeight * 24 / 8);
buff_img = (ImgBuffer *)calloc(1, sizeof(ImgBuffer));
if (buff_img == NULL) {
qDebug() << TIMEMS << "error in calloc";
::close(cameraHwnd);
return false;
}
struct v4l2_buffer buffer;
for (int index = 0; index < 1; index++) {
buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffer.memory = V4L2_MEMORY_MMAP;
buffer.index = index;
if (::ioctl(cameraHwnd, VIDIOC_QUERYBUF, &buffer) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_QUERYBUF";
::free(buff_img);
::close(cameraHwnd);
return false;
}
buff_img[index].length = buffer.length;
buff_img[index].start = (quint8 *)mmap(NULL, buffer.length, PROT_READ | PROT_WRITE, MAP_SHARED, cameraHwnd, buffer.m.offset);
if (MAP_FAILED == buff_img[index].start) {
qDebug() << TIMEMS << "error in mmap";
::free(buff_img);
::close(cameraHwnd);
return false;
}
//把缓冲帧放入队列
if (::ioctl(cameraHwnd, VIDIOC_QBUF, &buffer) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_QBUF";
for (int i = 0; i <= index; i++) {
munmap(buff_img[i].start, buff_img[i].length);
}
::free(buff_img);
::close(cameraHwnd);
return false;
}
}
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (::ioctl(cameraHwnd, VIDIOC_STREAMON, &type) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_STREAMON";
for (int i = 0; i < 1; i++) {
munmap(buff_img[i].start, buff_img[i].length);
}
::free(buff_img);
::close(cameraHwnd);
return false;
}
cameraOk = true;
#endif
qDebug() << TIMEMS << "open camera ok";
return cameraOk;
}
void CameraLinux::closeCamera()
{
#ifdef Q_OS_LINUX
if (cameraOk && buff_img != NULL) {
//停止摄像头采集
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (::ioctl(cameraHwnd, VIDIOC_STREAMOFF, &type) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_STREAMOFF";
}
//解除内存映射
for (int i = 0; i < 1; i++) {
munmap((buff_img)[i].start, (buff_img)[i].length);
}
//关闭设备文件
::close(cameraHwnd);
qDebug() << TIMEMS << "close camera ok";
}
//释放资源
::free(buff_img);
buff_img = NULL;
::free(buff_yuv422);
buff_yuv422 = NULL;
::free(buff_yuv420);
buff_yuv420 = NULL;
::free(buff_rgb24);
buff_rgb24 = NULL;
cameraOk = false;
cameraHwnd = -1;
#endif
}
int CameraLinux::readFrame()
{
int index = -1;
#ifdef Q_OS_LINUX
//等待摄像头采集到一桢数据
for (;;) {
fd_set fds;
struct timeval tv;
FD_ZERO(&fds);
FD_SET(cameraHwnd, &fds);
tv.tv_sec = 2;
tv.tv_usec = 0;
int r = ::select(cameraHwnd + 1, &fds, NULL, NULL, &tv);
if (-1 == r) {
if (EINTR == errno) {
continue;
}
return -1;
} else if (0 == r) {
return -1;
} else {
//采集到一张图片 跳出循环
break;
}
}
//从缓冲区取出一个缓冲帧
struct v4l2_buffer buffer;
buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buffer.memory = V4L2_MEMORY_MMAP;
if (::ioctl(cameraHwnd, VIDIOC_DQBUF, &buffer) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_DQBUF";
return -1;
}
memcpy(buff_yuv422, (uchar *)buff_img[buffer.index].start, buff_img[buffer.index].length);
//将取出的缓冲帧放回缓冲区
if (::ioctl(cameraHwnd, VIDIOC_QBUF, &buffer) < 0) {
qDebug() << TIMEMS << "error in VIDIOC_QBUF";
return -1;
}
index = buffer.index;
#endif
return index;
}“USB摄像头linux实现方法是什么”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注创新互联网站，小编将为大家输出更多高质量的实用文章！
