V4L2采集yuv视频花屏：Linux视频采集与编码（一）

这两天在Linux下用V4L2采集yuv视频然后用x264编码成h.264文件。

我将yuv视频保存到文件中，然后用pyuv播放器播放它，悲剧的是播放出来的视频花屏了。

如下所示：



我采集视频的参数为：

尺寸：640 * 480

YUV格式：YUYV即YUV422

我一直以为是我代码写错了，因为采集视频的程序我是参考V4L2官方示例代码的，并且我把官方示例代码来运行，发现采集的视频也是花屏的。然后我又猜想可能是我摄像头不能采集数据吗？可是我下载好几个camera都可以正常的拍照，录制视频。这样纠结了好久好久。直到我的手开始犯贱，我把pyuv播放器 Format中的 Interleaved 复选框勾起来了，奇迹出现了。pyuv上清清楚楚的显示出了我录制的视频 Orz

后来认真看代码发现我的设置中有这么一句：fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; 意思就是采集数据的时候使用的是隔行扫描的方式，也就是说我将采集到的yuv写到文件中的方式是用隔行扫描的方式保存。

于是如果不将 Interleaved复选框勾起来，播放器就不能正常的播放你的yuv文件。
下面是正常时候显示的图像：



嘿嘿，这是本人靓照 ^_^

yuv视频采集正常了，可是用x264编码出来的视频还是花屏到不堪入目！！！
这个是怎么办呢？请看我下一篇博文《YUYV编码成h.264：Linux视频采集与编码（二）》

附上V4L2视频采集代码：

/*
*  V4L2 video capture example
*
*  This program can be used and distributed without restrictions.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>             /* getopt_long() */

#include <fcntl.h>              /* low-level i/o */
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <asm/types.h>          /* for videodev2.h */

#include <linux/videodev2.h>

#define CLEAR(x) memset (&(x), 0, sizeof (x))

typedef enum {
IO_METHOD_READ, IO_METHOD_MMAP, IO_METHOD_USERPTR,
} io_method;

struct buffer {
void * start;
size_t length;
};

static char * dev_name = NULL;
static io_method io = IO_METHOD_MMAP;
static int fd = -1;
struct buffer * buffers = NULL;
static unsigned int n_buffers = 0;

FILE *fp;
char *filename = "test.yuv\0";

static void errno_exit(const char * s) {
fprintf(stderr, "%s error %d, %s/n", s, errno, strerror(errno));

exit(EXIT_FAILURE);
}

static int xioctl(int fd, int request, void * arg) {
int r;

do {
r = ioctl(fd, request, arg);
} while (-1 == r && EINTR == errno);

return r;
}

static void process_image(const void * p, int size) {
fwrite(p, size, 1, fp);
}

static int read_frame(void) {
struct v4l2_buffer buf;
unsigned int i;

switch (io) {
case IO_METHOD_READ:
if (-1 == read(fd, buffers[0].start, buffers[0].length)) {
switch (errno) {
case EAGAIN:
return 0;

case EIO:
/* Could ignore EIO, see spec. */
/* fall through */
default:
errno_exit("read");
}
}

process_image(buffers[0].start, buffers[0].length);

break;

case IO_METHOD_MMAP:
CLEAR(buf);

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;

if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
switch (errno) {
case EAGAIN:
return 0;

case EIO:
/* Could ignore EIO, see spec. */

/* fall through */

default:
errno_exit("VIDIOC_DQBUF");
}
}

assert(buf.index < n_buffers);

process_image(buffers[buf.index].start, buf.length);

if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");

break;

case IO_METHOD_USERPTR:
CLEAR(buf);

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_USERPTR;

if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
switch (errno) {
case EAGAIN:
return 0;

case EIO:
/* Could ignore EIO, see spec. */

/* fall through */

default:
errno_exit("VIDIOC_DQBUF");
}
}

for (i = 0; i < n_buffers; ++i)
if (buf.m.userptr == (unsigned long) buffers[i].start
&& buf.length == buffers[i].length)
break;

assert(i < n_buffers);

process_image((void *) buf.m.userptr, buf.length);

if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");

break;
}

return 1;
}

static void mainloop(void) {
unsigned int count;

count = 100;

while (count-- > 0) {
for (;;) {
fd_set fds;
struct timeval tv;
int r;

FD_ZERO(&fds);
FD_SET(fd, &fds);

/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;

r = select(fd + 1, &fds, NULL, NULL, &tv);

if (-1 == r) {
if (EINTR == errno)
continue;

errno_exit("select");
}

if (0 == r) {
fprintf(stderr, "select timeout/n");
exit(EXIT_FAILURE);
}

if (read_frame())
break;

/* EAGAIN - continue select loop. */
}
}
}

static void stop_capturing(void) {
enum v4l2_buf_type type;

switch (io) {
case IO_METHOD_READ:
/* Nothing to do. */
break;

case IO_METHOD_MMAP:
case IO_METHOD_USERPTR:
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
errno_exit("VIDIOC_STREAMOFF");

break;
}
}

static void start_capturing(void) {
unsigned int i;
enum v4l2_buf_type type;

switch (io) {
case IO_METHOD_READ:
/* Nothing to do. */
break;

case IO_METHOD_MMAP:
for (i = 0; i < n_buffers; ++i) {
struct v4l2_buffer buf;

CLEAR(buf);

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;

if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
}

type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
errno_exit("VIDIOC_STREAMON");

break;

case IO_METHOD_USERPTR:
for (i = 0; i < n_buffers; ++i) {
struct v4l2_buffer buf;

CLEAR(buf);

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_USERPTR;
buf.index = i;
buf.m.userptr = (unsigned long) buffers[i].start;
buf.length = buffers[i].length;

if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
}

type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
errno_exit("VIDIOC_STREAMON");

break;
}
}

static void uninit_device(void) {
unsigned int i;

switch (io) {
case IO_METHOD_READ:
free(buffers[0].start);
break;

case IO_METHOD_MMAP:
for (i = 0; i < n_buffers; ++i)
if (-1 == munmap(buffers[i].start, buffers[i].length))
errno_exit("munmap");
break;

case IO_METHOD_USERPTR:
for (i = 0; i < n_buffers; ++i)
free(buffers[i].start);
break;
}

free(buffers);
}

static void init_read(unsigned int buffer_size) {
buffers = calloc(1, sizeof(*buffers));

if (!buffers) {
fprintf(stderr, "Out of memory/n");
exit(EXIT_FAILURE);
}

buffers[0].length = buffer_size;
buffers[0].start = malloc(buffer_size);

if (!buffers[0].start) {
fprintf(stderr, "Out of memory/n");
exit(EXIT_FAILURE);
}
}

static void init_mmap(void) {
struct v4l2_requestbuffers req;

CLEAR(req);

req.count = 4;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;

if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
if (EINVAL == errno) {
fprintf(stderr, "%s does not support "
"memory mapping/n", dev_name);
exit(EXIT_FAILURE);
} else {
errno_exit("VIDIOC_REQBUFS");
}
}

if (req.count < 2) {
fprintf(stderr, "Insufficient buffer memory on %s/n", dev_name);
exit(EXIT_FAILURE);
}

buffers = calloc(req.count, sizeof(*buffers));

if (!buffers) {
fprintf(stderr, "Out of memory/n");
exit(EXIT_FAILURE);
}

for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
struct v4l2_buffer buf;

CLEAR(buf);

buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;

if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
errno_exit("VIDIOC_QUERYBUF");

buffers[n_buffers].length = buf.length;
buffers[n_buffers].start = mmap(NULL /* start anywhere */, buf.length,
PROT_READ | PROT_WRITE /* required */,
MAP_SHARED /* recommended */, fd, buf.m.offset);

if (MAP_FAILED == buffers[n_buffers].start)
errno_exit("mmap");
}
}

static void init_userp(unsigned int buffer_size) {
struct v4l2_requestbuffers req;
unsigned int page_size;

page_size = getpagesize();
buffer_size = (buffer_size + page_size - 1) & ~(page_size - 1);

CLEAR(req);

req.count = 4;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_USERPTR;

if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
if (EINVAL == errno) {
fprintf(stderr, "%s does not support "
"user pointer i/o/n", dev_name);
exit(EXIT_FAILURE);
} else {
errno_exit("VIDIOC_REQBUFS");
}
}

buffers = calloc(4, sizeof(*buffers));

if (!buffers) {
fprintf(stderr, "Out of memory/n");
exit(EXIT_FAILURE);
}

for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
buffers[n_buffers].length = buffer_size;
buffers[n_buffers].start = memalign(/* boundary */page_size,
buffer_size);

if (!buffers[n_buffers].start) {
fprintf(stderr, "Out of memory/n");
exit(EXIT_FAILURE);
}
}
}

static void init_device(void) {
struct v4l2_capability cap;
struct v4l2_cropcap cropcap;
struct v4l2_crop crop;
struct v4l2_format fmt;
unsigned int min;

if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
if (EINVAL == errno) {
fprintf(stderr, "%s is no V4L2 device/n", dev_name);
exit(EXIT_FAILURE);
} else {
errno_exit("VIDIOC_QUERYCAP");
}
}

if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
fprintf(stderr, "%s is no video capture device/n", dev_name);
exit(EXIT_FAILURE);
}

switch (io) {
case IO_METHOD_READ:
if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
fprintf(stderr, "%s does not support read i/o/n", dev_name);
exit(EXIT_FAILURE);
}

break;

case IO_METHOD_MMAP:
case IO_METHOD_USERPTR:
if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
fprintf(stderr, "%s does not support streaming i/o/n", dev_name);
exit(EXIT_FAILURE);
}

break;
}

/* Select video input, video standard and tune here. */

CLEAR(cropcap);

cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
crop.c = cropcap.defrect; /* reset to default */

if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) {
switch (errno) {
case EINVAL:
/* Cropping not supported. */
break;
default:
/* Errors ignored. */
break;
}
}
} else {
/* Errors ignored. */
}

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_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;

if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
errno_exit("VIDIOC_S_FMT");

/* Note VIDIOC_S_FMT may change width and height. */

/* Buggy driver paranoia. */
min = fmt.fmt.pix.width * 2;
if (fmt.fmt.pix.bytesperline < min)
fmt.fmt.pix.bytesperline = min;
min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
if (fmt.fmt.pix.sizeimage < min)
fmt.fmt.pix.sizeimage = min;

switch (io) {
case IO_METHOD_READ:
init_read(fmt.fmt.pix.sizeimage);
break;

case IO_METHOD_MMAP:
init_mmap();
break;

case IO_METHOD_USERPTR:
init_userp(fmt.fmt.pix.sizeimage);
break;
}
}

static void close_device(void) {
if (-1 == close(fd))
errno_exit("close");

fd = -1;
}

static void open_device(void) {
struct stat st;

if (-1 == stat(dev_name, &st)) {
fprintf(stderr, "Cannot identify '%s': %d, %s/n", dev_name, errno,
strerror(errno));
exit(EXIT_FAILURE);
}

if (!S_ISCHR(st.st_mode)) {
fprintf(stderr, "%s is no device/n", dev_name);
exit(EXIT_FAILURE);
}

fd = open(dev_name, O_RDWR /* required */| O_NONBLOCK, 0);

if (-1 == fd) {
fprintf(stderr, "Cannot open '%s': %d, %s/n", dev_name, errno,
strerror(errno));
exit(EXIT_FAILURE);
}
}

static void usage(FILE * fp, int argc, char ** argv) {
fprintf(fp, "Usage: %s [options]/n/n"
"Options:/n"
"-d | --device name   Video device name [/dev/video]/n"
"-h | --help          Print this message/n"
"-m | --mmap          Use memory mapped buffers/n"
"-r | --read          Use read() calls/n"
"-u | --userp         Use application allocated buffers/n"
"", argv[0]);
}

static const char short_options[] = "d:hmru";

static const struct option long_options[] = { { "device", required_argument,
NULL, 'd' }, { "help", no_argument, NULL, 'h' }, { "mmap", no_argument,
NULL, 'm' }, { "read", no_argument, NULL, 'r' }, { "userp", no_argument,
NULL, 'u' }, { 0, 0, 0, 0 } };

int main(int argc, char ** argv) {
dev_name = "/dev/video0";

for (;;) {
int index;
int c;

c = getopt_long(argc, argv, short_options, long_options, &index);

if (-1 == c)
break;

switch (c) {
case 0: /* getopt_long() flag */
break;

case 'd':
dev_name = optarg;
break;

case 'h':
usage(stdout, argc, argv);
exit(EXIT_SUCCESS);

case 'm':
io = IO_METHOD_MMAP;
break;

case 'r':
io = IO_METHOD_READ;
break;

case 'u':
io = IO_METHOD_USERPTR;
break;

default:
usage(stderr, argc, argv);
exit(EXIT_FAILURE);
}
}

open_device();

init_device();

start_capturing();

fp = fopen(filename, "wa+");
mainloop();
fclose(fp);

stop_capturing();

uninit_device();

close_device();

exit(EXIT_SUCCESS);

return 0;
}