在做网络视频监控系统时，摄像头有的不支持v4l2_pix_fmt_mjpeg格式，只能支持v4l2_pix_fmt_yuyv格式，这样的话，不适合于在网络上的传输。为了将YUYV转换成MJPEG,我借助于jpeg库。
)jpeg源码包通过下面这个网址下载
http://www.ijg.org/files/jpegsrc.v8b.tar.gz
2)解压源码包
$ tar xzvf jpegsrc.v8b.tar.gz
$ cd jpeg-8b
$ ./configure --prefix=/usr/local/jpeg
$ make
$ make install
2)具体用法：
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "print.h"
#define OUTPUT_BUF_SIZE 4096
#define WIDTH 640
#define HEIGHT 480
struct buffer {
void * start;
size_t length;
};
typedef struct {
struct jpeg_destination_mgr pub;
JOCTET * buffer;
unsigned char *outbuffer;
int outbuffer_size;
unsigned char *outbuffer_cursor;
int *written;
}mjpg_destination_mgr;
typedef mjpg_destination_mgr *mjpg_dest_ptr;
static int fd= -1;
struct buffer *buffers= NULL;
static unsigned int n_buffers= 0;
char *temp_buffer =NULL;
METHODDEF(void) init_destination(j_compress_ptr cinfo) {
mjpg_dest_ptr dest = (mjpg_dest_ptr) cinfo->dest;
dest->buffer = (JOCTET *)(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, OUTPUT_BUF_SIZE * sizeof(JOCTET));
*(dest->written) = 0;
dest->pub.next_output_byte = dest->buffer;
dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
}
METHODDEF(boolean) empty_output_buffer(j_compress_ptr cinfo) {
mjpg_dest_ptr dest = (mjpg_dest_ptr) cinfo->dest;
memcpy(dest->outbuffer_cursor, dest->buffer, OUTPUT_BUF_SIZE);
dest->outbuffer_cursor += OUTPUT_BUF_SIZE;
*(dest->written) += OUTPUT_BUF_SIZE;
dest->pub.next_output_byte = dest->buffer;
dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
return TRUE;
}
METHODDEF(void) term_destination(j_compress_ptr cinfo) {
mjpg_dest_ptr dest = (mjpg_dest_ptr) cinfo->dest;
size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
/* Write any data remaining in the buffer */
memcpy(dest->outbuffer_cursor, dest->buffer, datacount);
dest->outbuffer_cursor += datacount;
*(dest->written) += datacount;
}
void dest_buffer(j_compress_ptr cinfo, unsigned char *buffer, int size, int *written) {
mjpg_dest_ptr dest;
if (cinfo->dest == NULL) {
cinfo->dest = (struct jpeg_destination_mgr *)(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, sizeof(mjpg_destination_mgr));
}
dest = (mjpg_dest_ptr)cinfo->dest;
dest->pub.init_destination = init_destination;
dest->pub.empty_output_buffer = empty_output_buffer;
dest->pub.term_destination = term_destination;
dest->outbuffer = buffer;
dest->outbuffer_size = size;
dest->outbuffer_cursor = buffer;
dest->written = written;
}
//摄像头采集帧图像的YUYV格式转换为JPEG格式
int compress_yuyv_to_jpeg(unsigned char *buf, unsigned char *buffer, int size, int quality) {
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
JSAMPROW row_pointer[1];
unsigned char *line_buffer, *yuyv;
int z;
static int written;
//int count = 0;
//printf("%s\n", buf);
line_buffer = calloc (WIDTH * 3, 1);
yuyv = buf;//将YUYV格式的图片数据赋给YUYV指针
printf("compress start...\n");
cinfo.err = jpeg_std_error (&jerr);
jpeg_create_compress (&cinfo);
/* jpeg_stdio_dest (&cinfo, file); */
dest_buffer(&cinfo, buffer, size, &written);
cinfo.image_width = WIDTH;
cinfo.image_height = HEIGHT;
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults (&cinfo);
jpeg_set_quality (&cinfo, quality, TRUE);
jpeg_start_compress (&cinfo, TRUE);
z = 0;
while (cinfo.next_scanline < HEIGHT) {
int x;
unsigned char *ptr = line_buffer;
for (x = 0; x < WIDTH; x++) {
int r, g, b;
int y, u, v;
if (!z)
y = yuyv[0] << 8;
else
y = yuyv[2] << 8;
u = yuyv[1] - 128;
v = yuyv[3] - 128;
r = (y + (359 * v)) >> 8;
g = (y - (88 * u) - (183 * v)) >> 8;
b = (y + (454 * u)) >> 8;
*(ptr++) = (r > 255) ? 255 : ((r < 0) ? 0 : r);
*(ptr++) = (g > 255) ? 255 : ((g < 0) ? 0 : g);
*(ptr++) = (b > 255) ? 255 : ((b < 0) ? 0 : b);
if (z++) {
z = 0;
yuyv += 4;
}
}
row_pointer[0] = line_buffer;
jpeg_write_scanlines (&cinfo, row_pointer, 1);
}
jpeg_finish_compress (&cinfo);
jpeg_destroy_compress (&cinfo);
free (line_buffer);
return (written);
}
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