友善之臂视频监控方案源码学习(6) - 视频采集

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【问题描述】在友善之臂视频监控方案源码学习(5) - 输入控制一文中，介绍了input_run完成的功能。本文结合input_run实现的视频采集线程对视频采集进行详细分析。

【解析】

1 涉及到的文件和目录

mjpg-streamer-mini2440-read-only/start_uvc.sh

mjpg-streamer-mini2440-read-only/mjpg_streamer.c

mjpg-streamer-mini2440-read-only/mjpg_streamer.h

mjpg-streamer-mini2440-read-only/plugins/input.h

mjpg-streamer-mini2440-read-only/plugins/input_uvc

2 视频设备初始化

视频设备初始化在input_init函数中完成（mjpg-streamer-mini2440-read-only/plugins/input_uvc/input_uvc.c）：

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/* open video device and prepare data structure */

if (init_videoIn(videoIn, dev, width, height, fps, format, 1) < 0) {

IPRINT("init_VideoIn failed\n");

closelog();

exit(EXIT_FAILURE);

}

init_videoIn函数中调用的视频初始化代码如下（mjpg-streamer-mini2440-read-only/plugins/input_uvc/V412uvc.c）：

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if (init_v4l2 (vd) < 0) {

fprintf (stderr, " Init v4L2 failed !! exit fatal \n");

goto error;;

}

init_v412代码如下（mjpg-streamer-mini2440-read-only/plugins/input_uvc/V412uvc.c）：

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static int init_v4l2(struct vdIn *vd)

{

int i;

int ret = 0;

if ((vd->fd = open(vd->videodevice, O_RDWR)) == -1) {

perror("ERROR opening V4L interface");

return -1;

}

memset(&vd->cap, 0, sizeof(struct v4l2_capability));

ret = ioctl(vd->fd, VIDIOC_QUERYCAP, &vd->cap);

if (ret < 0) {

fprintf(stderr, "Error opening device %s: unable to query device.\n", vd->videodevice);

goto fatal;

}

if ((vd->cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0) {

fprintf(stderr, "Error opening device %s: video capture not supported.\n",

vd->videodevice);

goto fatal;;

}

if (vd->grabmethod) {

if (!(vd->cap.capabilities & V4L2_CAP_STREAMING)) {

fprintf(stderr, "%s does not support streaming i/o\n", vd->videodevice);

goto fatal;

}

} else {

if (!(vd->cap.capabilities & V4L2_CAP_READWRITE)) {

fprintf(stderr, "%s does not support read i/o\n", vd->videodevice);

goto fatal;

}

}

/*

* set format in

*/

memset(&vd->fmt, 0, sizeof(struct v4l2_format));

vd->fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->fmt.fmt.pix.width = vd->width;

vd->fmt.fmt.pix.height = vd->height;

vd->fmt.fmt.pix.pixelformat = vd->formatIn;

vd->fmt.fmt.pix.field = V4L2_FIELD_ANY;

ret = ioctl(vd->fd, VIDIOC_S_FMT, &vd->fmt);

if (ret < 0) {

perror("Unable to set format");

goto fatal;

}

if ((vd->fmt.fmt.pix.width != vd->width) ||

(vd->fmt.fmt.pix.height != vd->height)) {

fprintf(stderr, " format asked unavailable get width %d height %d \n", vd->fmt.fmt.pix.width, vd->fmt.fmt.pix.height);

vd->width = vd->fmt.fmt.pix.width;

vd->height = vd->fmt.fmt.pix.height;

/*

* look the format is not part of the deal ???

*/

}

if(vd->fmt.fmt.pix.pixelformat!=vd->formatIn)

{

char fourcc1[5]={0,0,0,0,0};

char fourcc2[5]={0,0,0,0,0};

memmove(fourcc1,(char*)&vd->formatIn,4);

memmove(fourcc2,(char*)&vd->fmt.fmt.pix.pixelformat,4);

fprintf(stderr, " requested %s but got %s format instead\n",fourcc1,fourcc2);

vd->formatIn = vd->fmt.fmt.pix.pixelformat;

}

/*

* set framerate

*/

struct v4l2_streamparm *setfps;

setfps = (struct v4l2_streamparm *) calloc(1, sizeof(struct v4l2_streamparm));

memset(setfps, 0, sizeof(struct v4l2_streamparm));

setfps->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

setfps->parm.capture.timeperframe.numerator = 1;

setfps->parm.capture.timeperframe.denominator = vd->fps;

ret = ioctl(vd->fd, VIDIOC_S_PARM, setfps);

/*

* request buffers

*/

memset(&vd->rb, 0, sizeof(struct v4l2_requestbuffers));

vd->rb.count = NB_BUFFER;

vd->rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->rb.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_REQBUFS, &vd->rb);

if (ret < 0) {

perror("Unable to allocate buffers");

goto fatal;

}

/*

* map the buffers

*/

for (i = 0; i < NB_BUFFER; i++) {

memset(&vd->buf, 0, sizeof(struct v4l2_buffer));

vd->buf.index = i;

vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->buf.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_QUERYBUF, &vd->buf);

if (ret < 0) {

perror("Unable to query buffer");

goto fatal;

}

if (debug)

fprintf(stderr, "length: %u offset: %u\n", vd->buf.length, vd->buf.m.offset);

vd->mem[i] = mmap(0 /* start anywhere */ ,

vd->buf.length, PROT_READ, MAP_SHARED, vd->fd,

vd->buf.m.offset);

if (vd->mem[i] == MAP_FAILED) {

perror("Unable to map buffer");

goto fatal;

}

if (debug)

fprintf(stderr, "Buffer mapped at address %p.\n", vd->mem[i]);

}

/*

* Queue the buffers.

*/

for (i = 0; i < NB_BUFFER; ++i) {

memset(&vd->buf, 0, sizeof(struct v4l2_buffer));

vd->buf.index = i;

vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->buf.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_QBUF, &vd->buf);

if (ret < 0) {

perror("Unable to queue buffer");

goto fatal;;

}

}

return 0;

fatal:

return -1;

}

该部分主要完成了下述功能：

(1) 打开视频设备

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if ((vd->fd = open(vd->videodevice, O_RDWR)) == -1) {

perror("ERROR opening V4L interface");

return -1;

}

(2) 开启捕获功能

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memset(&vd->cap, 0, sizeof(struct v4l2_capability));

ret = ioctl(vd->fd, VIDIOC_QUERYCAP, &vd->cap);

if (ret < 0) {

fprintf(stderr, "Error opening device %s: unable to query device.\n", vd->videodevice);

goto fatal;

}

if ((vd->cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0) {

fprintf(stderr, "Error opening device %s: video capture not supported.\n",

vd->videodevice);

goto fatal;;

}

if (vd->grabmethod) {

if (!(vd->cap.capabilities & V4L2_CAP_STREAMING)) {

fprintf(stderr, "%s does not support streaming i/o\n", vd->videodevice);

goto fatal;

}

} else {

if (!(vd->cap.capabilities & V4L2_CAP_READWRITE)) {

fprintf(stderr, "%s does not support read i/o\n", vd->videodevice);

goto fatal;

}

}

(3) 设置视频格式

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/*

* set format in

*/

memset(&vd->fmt, 0, sizeof(struct v4l2_format));

vd->fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->fmt.fmt.pix.width = vd->width;

vd->fmt.fmt.pix.height = vd->height;

vd->fmt.fmt.pix.pixelformat = vd->formatIn;

vd->fmt.fmt.pix.field = V4L2_FIELD_ANY;

ret = ioctl(vd->fd, VIDIOC_S_FMT, &vd->fmt);

if (ret < 0) {

perror("Unable to set format");

goto fatal;

}

if ((vd->fmt.fmt.pix.width != vd->width) ||

(vd->fmt.fmt.pix.height != vd->height)) {

fprintf(stderr, " format asked unavailable get width %d height %d \n", vd->fmt.fmt.pix.width, vd->fmt.fmt.pix.height);

vd->width = vd->fmt.fmt.pix.width;

vd->height = vd->fmt.fmt.pix.height;

/*

* look the format is not part of the deal ???

*/

}

if(vd->fmt.fmt.pix.pixelformat!=vd->formatIn)

{

char fourcc1[5]={0,0,0,0,0};

char fourcc2[5]={0,0,0,0,0};

memmove(fourcc1,(char*)&vd->formatIn,4);

memmove(fourcc2,(char*)&vd->fmt.fmt.pix.pixelformat,4);

fprintf(stderr, " requested %s but got %s format instead\n",fourcc1,fourcc2);

vd->formatIn = vd->fmt.fmt.pix.pixelformat;

}

(4) 设置帧速率

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/*

* set framerate

*/

struct v4l2_streamparm *setfps;

setfps = (struct v4l2_streamparm *) calloc(1, sizeof(struct v4l2_streamparm));

memset(setfps, 0, sizeof(struct v4l2_streamparm));

setfps->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

setfps->parm.capture.timeperframe.numerator = 1;

setfps->parm.capture.timeperframe.denominator = vd->fps;

ret = ioctl(vd->fd, VIDIOC_S_PARM, setfps);

(5) 设置缓存

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/*

* request buffers

*/

memset(&vd->rb, 0, sizeof(struct v4l2_requestbuffers));

vd->rb.count = NB_BUFFER;

vd->rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->rb.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_REQBUFS, &vd->rb);

if (ret < 0) {

perror("Unable to allocate buffers");

goto fatal;

}

/*

* map the buffers

*/

for (i = 0; i < NB_BUFFER; i++) {

memset(&vd->buf, 0, sizeof(struct v4l2_buffer));

vd->buf.index = i;

vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->buf.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_QUERYBUF, &vd->buf);

if (ret < 0) {

perror("Unable to query buffer");

goto fatal;

}

if (debug)

fprintf(stderr, "length: %u offset: %u\n", vd->buf.length, vd->buf.m.offset);

vd->mem[i] = mmap(0 /* start anywhere */ ,

vd->buf.length, PROT_READ, MAP_SHARED, vd->fd,

vd->buf.m.offset);

if (vd->mem[i] == MAP_FAILED) {

perror("Unable to map buffer");

goto fatal;

}

if (debug)

fprintf(stderr, "Buffer mapped at address %p.\n", vd->mem[i]);

}

/*

* Queue the buffers.

*/

for (i = 0; i < NB_BUFFER; ++i) {

memset(&vd->buf, 0, sizeof(struct v4l2_buffer));

vd->buf.index = i;

vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->buf.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_QBUF, &vd->buf);

if (ret < 0) {

perror("Unable to queue buffer");

goto fatal;;

}

3 视频采集

在input_run中调用了视频采集的线程函数，如下所示：

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int input_run(void) {

pglobal->buf = malloc(videoIn->framesizeIn);

if (pglobal->buf == NULL) {

fprintf(stderr, "could not allocate memory\n");

exit(EXIT_FAILURE);

}

pthread_create(&cam, 0, cam_thread, NULL);

pthread_detach(cam);

return 0;

}

cam_thread定义如下：

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void *cam_thread( void *arg ) {

/* set cleanup handler to cleanup allocated ressources */

pthread_cleanup_push(cam_cleanup, NULL);

while( !pglobal->stop ) {

/* grab a frame */

if( uvcGrab(videoIn) < 0 ) {

IPRINT("Error grabbing frames\n");

exit(EXIT_FAILURE);

}

DBG("received frame of size: %d\n", videoIn->buf.bytesused);

/*

* Workaround for broken, corrupted frames:

* Under low light conditions corrupted frames may get captured.

* The good thing is such frames are quite small compared to the regular pictures.

* For example a VGA (640x480) webcam picture is normally >= 8kByte large,

* corrupted frames are smaller.

*/

if ( videoIn->buf.bytesused < minimum_size ) {

DBG("dropping too small frame, assuming it as broken\n");

continue;

}

/* copy JPG picture to global buffer */

pthread_mutex_lock( &pglobal->db );

/*

* If capturing in YUV mode convert to JPEG now.

* This compression requires many CPU cycles, so try to avoid YUV format.

* Getting JPEGs straight from the webcam, is one of the major advantages of

* Linux-UVC compatible devices.

*/

if (videoIn->formatIn != V4L2_PIX_FMT_MJPEG) {

DBG("compressing frame\n");

pglobal->size = compress_yuyv_to_jpeg(videoIn, pglobal->buf, videoIn->framesizeIn, gquality, videoIn->formatIn);

}

else {

DBG("copying frame\n");

pglobal->size = memcpy_picture(pglobal->buf, videoIn->tmpbuffer, videoIn->buf.bytesused);

}

#if 0

/* motion detection can be done just by comparing the picture size, but it is not very accurate!! */

if ( (prev_size - global->size)*(prev_size - global->size) > 4*1024*1024 ) {

DBG("motion detected (delta: %d kB)\n", (prev_size - global->size) / 1024);

}

prev_size = global->size;

#endif

/* signal fresh_frame */

pthread_cond_broadcast(&pglobal->db_update);

pthread_mutex_unlock( &pglobal->db );

DBG("waiting for next frame\n");

/* only use usleep if the fps is below 5, otherwise the overhead is too long */

if ( videoIn->fps < 5 ) {

usleep(1000*1000/videoIn->fps);

}

}

DBG("leaving input thread, calling cleanup function now\n");

pthread_cleanup_pop(1);

return NULL;

}

该函数完成下述任务：

(1) 视频抓取

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while( !pglobal->stop ) {

/* grab a frame */

if( uvcGrab(videoIn) < 0 ) {

IPRINT("Error grabbing frames\n");

exit(EXIT_FAILURE);

}

uvcGrab函数实现如下：

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int uvcGrab(struct vdIn *vd)

{

#define HEADERFRAME1 0xaf

int ret;

if (!vd->isstreaming)

if (video_enable(vd))

goto err;

memset(&vd->buf, 0, sizeof(struct v4l2_buffer));

vd->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

vd->buf.memory = V4L2_MEMORY_MMAP;

ret = ioctl(vd->fd, VIDIOC_DQBUF, &vd->buf);

if (ret < 0) {

perror("Unable to dequeue buffer");

goto err;

}

switch (vd->formatIn) {

case V4L2_PIX_FMT_MJPEG:

if (vd->buf.bytesused <= HEADERFRAME1) { /* Prevent crash

* on empty image */

fprintf(stderr, "Ignoring empty buffer ...\n");

return 0;

}

/* memcpy(vd->tmpbuffer, vd->mem[vd->buf.index], vd->buf.bytesused);

memcpy (vd->tmpbuffer, vd->mem[vd->buf.index], HEADERFRAME1);

memcpy (vd->tmpbuffer + HEADERFRAME1, dht_data, sizeof(dht_data));

memcpy (vd->tmpbuffer + HEADERFRAME1 + sizeof(dht_data), vd->mem[vd->buf.index] + HEADERFRAME1, (vd->buf.bytesused - HEADERFRAME1));

*/

memcpy(vd->tmpbuffer, vd->mem[vd->buf.index], vd->buf.bytesused);

if (debug)

fprintf(stderr, "bytes in used %d \n", vd->buf.bytesused);

break;

case V4L2_PIX_FMT_YUYV:

default:

if (vd->buf.bytesused > vd->framesizeIn)

memcpy (vd->framebuffer, vd->mem[vd->buf.index], (size_t) vd->framesizeIn);

else

memcpy (vd->framebuffer, vd->mem[vd->buf.index], (size_t) vd->buf.bytesused);

break;

//goto err;

break;

}

ret = ioctl(vd->fd, VIDIOC_QBUF, &vd->buf);

if (ret < 0) {

perror("Unable to requeue buffer");

goto err;

}

return 0;

err:

vd->signalquit = 0;

return -1;

}

该函数主要完成了下述功能：

(a) 使能视频设备

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if (!vd->isstreaming)

if (video_enable(vd))

goto err;

实质上是调用了下述方法：

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ret = ioctl(vd->fd, VIDIOC_STREAMON, &type);

if (ret < 0) {

perror("Unable to start capture");

return ret;

}

(b) 视频采集

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ret = ioctl(vd->fd, VIDIOC_DQBUF, &vd->buf);

if (ret < 0) {

perror("Unable to dequeue buffer");

goto err;

}

注：采集的视频信息放在vd->buf中。

(2) 视频压缩编码

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if (videoIn->formatIn != V4L2_PIX_FMT_MJPEG) {

DBG("compressing frame\n");

pglobal->size = compress_yuyv_to_jpeg(videoIn, pglobal->buf, videoIn->framesizeIn, gquality, videoIn->formatIn);

}

else {

DBG("copying frame\n");

pglobal->size = memcpy_picture(pglobal->buf, videoIn->tmpbuffer, videoIn->buf.bytesused);

}

此过程，后续文章进行详述。

4 视频的存储

视频采集的信息存储在vd->buf中，vd->buf怎么和global->buf联系起来的呢？

(1) input_init初始化全局指针

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pglobal = param->global;

param->global指针指向mjpg-streamer-mini2440-read-only/mjpg_streamer.c主程序main中的global全局指针。

(2) input_run中分配空间

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pglobal->buf = malloc(videoIn->framesizeIn);

if (pglobal->buf == NULL) {

fprintf(stderr, "could not allocate memory\n");

exit(EXIT_FAILURE);

}

(3) cam_thread抓取

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while( !pglobal->stop ) {

/* grab a frame */

if( uvcGrab(videoIn) < 0 ) {

IPRINT("Error grabbing frames\n");

exit(EXIT_FAILURE);

}

抓取的数据存储在videoIn结构中：

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int uvcGrab(struct vdIn *vd)

{

...

ret = ioctl(vd->fd, VIDIOC_DQBUF, &vd->buf);

if (ret < 0) {

perror("Unable to dequeue buffer");

goto err;

}

}

(4) global->buf和videoIn->buf的联系

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if (videoIn->formatIn != V4L2_PIX_FMT_MJPEG) {

DBG("compressing frame\n");

pglobal->size = compress_yuyv_to_jpeg(videoIn, pglobal->buf, videoIn->framesizeIn, gquality, videoIn->formatIn);

}

else {

DBG("copying frame\n");

pglobal->size = memcpy_picture(pglobal->buf, videoIn->tmpbuffer, videoIn->buf.bytesused);

}

最终，通过压缩编码将videoIn->buf的数据存储在global->buf中。

【源码下载】

http://download.csdn.net/detail/tandesir/4915905

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