最近大部分时间都在研究usb 摄像头顺便把jpg编码也写上　下面大部分函数都是我在网上找的　然后稍微的改一点就可以使用了　不过找这些函数费了不少时间　jpg编码网上有很多说明　大致流程都是一样的　我也没深入研究这里就不说了　接前面几篇Camera的文章　这里主要同把获取到的yuv数据通过jpg压缩　以及压缩成mjpeg视频流 首先说明下摄像头获取到的数据格式是yuv422(p16) 这个是在你初始化摄像头设置pixelformat我们当初设置的是V4L2_PIX_FMT_YUYV它的实际格式就是yuv422了　具体的格式你就上网找吧　具体过程是　首先将yuv422转换成rgb888然后在将rgb888转换成jpg　其实是可以直接将yuv422转成jpg的但是我没实现后面我们也放上相关的代码　下面我就直接上代码了

首先yuv422转rgb888

static void YUV422toRGB888(int width, int height, unsigned char *src, unsigned char *dst)
{
	int line, column;
	unsigned char *py, *pu, *pv;
	unsigned char *tmp = dst;
	/* In this format each four bytes is two pixels. Each four bytes is two Y's, aCb 
	and a Cr.Each Y goes to one of the pixels, and the Cb and Cr belong to bothpixels. */
	py = src;
	pu = src + 1;
	pv = src + 3;
	#define CLIP(x) ( (x)>=0xFF ? 0xFF : ( (x) <= 0x00 ? 0x00 : (x) ) )
	for (line = 0; line < height; ++line) {
		for (column = 0; column < width; ++column) {
			*tmp++ = CLIP((double)*py + 1.402*((double)*pv-128.0));
			*tmp++ = CLIP((double)*py - 0.344*((double)*pu-128.0) -0.714*((double)*pv-128.0));
			*tmp++ = CLIP((double)*py + 1.772*((double)*pu-128.0));
			// increase py every time
			py += 2;
			// increase pu,pv every second time
			if ((column & 1)==1) {
				pu += 4;
				pv += 4;
			}
		}
	}
}

static int jpeg_mem_copy(unsigned char* img,unsigned char *dest)
{
	struct jpeg_compress_struct cinfo;
	struct jpeg_error_mgr jerr;
	JSAMPROW row_pointer[1];
  	unsigned char *pbuf = NULL;
	int jpglen = 0;
	// create jpeg data
	cinfo.err = jpeg_std_error( &jerr );
	jpeg_create_compress(&cinfo);
	//jpeg_stdio_dest(&cinfo, fp);
	jpeg_mem_dest(&cinfo, &pbuf, &jpglen);
	// set image parameters
	cinfo.image_width = mwidth;
	cinfo.image_height = mheight;
	cinfo.input_components = 3;
	cinfo.in_color_space = JCS_RGB;
	// set jpeg compression parameters to default
	jpeg_set_defaults(&cinfo);
	// and then adjust quality setting
	jpeg_set_quality(&cinfo, 80, TRUE);
	// start compress
	jpeg_start_compress(&cinfo, TRUE);
	// feed data
	while (cinfo.next_scanline < cinfo.image_height) {
		row_pointer[0] = &img[cinfo.next_scanline * cinfo.image_width * 
		cinfo.input_components];
		jpeg_write_scanlines(&cinfo, row_pointer, 1);
	}
	// finish compression
	jpeg_finish_compress(&cinfo);
	// destroy jpeg data
	jpeg_destroy_compress(&cinfo);
    memcpy(dest,pbuf,jpglen);
	//LOGD("++++++++++++++++len is %d\n",jpglen);
	if(pbuf)
		free(pbuf);
    return jpglen;
}

下面是我提供给上层调用的一个接口

JNIEXPORT jint JNICALL Java_com_hclydao_usbcamera_Fimcgzsd_writefile(JNIEnv * env, jclass obj,jbyteArray yuvdata,jbyteArray filename)//jintArray rgbdata
{
	jbyte *ydata = http://www.mamicode.com/(jbyte*)(*env)->GetByteArrayElements(env, yuvdata, 0);>这个传入的是获取到的yuv数据以及要保存的jpg文件的路径 里面有一些参数是我声明的全局变量　具体可以去看我前面几篇文章

以下是视频流的相关接口
FILE * video_file;
/*
 *put in frame buffer to queue
 */
JNIEXPORT jint JNICALL Java_com_hclydao_usbcamera_Fimcgzsd_videoopen(JNIEnv * env, jclass obj,jbyteArray filename)
{
	jbyte *filedir = (jbyte*)(*env)->GetByteArrayElements(env, filename, 0);

  	if ((video_file = fopen(filedir, "wb")) == NULL) {
    	LOGE("++++++++++++open %s failed\n",filedir);
    	return -1;
  	}

	(*env)->ReleaseByteArrayElements(env, filename, filedir, 0);
}

JNIEXPORT jint JNICALL Java_com_hclydao_usbcamera_Fimcgzsd_videostart(JNIEnv * env, jclass obj,jbyteArray yuvdata)
{
	jbyte *ydata = http://www.mamicode.com/(jbyte*)(*env)->GetByteArrayElements(env, yuvdata, 0);>就是连续保存jpg文件到同一个文件 保存的文件直接播放不了　用格式工厂转换成avi以后就可以放了

下面是一个直接将yuv转jpg的函数　这是将yuv420p转成jpg的 我的是yuv422的　改了很多次发现保存的图片不对　看来还是要研究下这些格式之间的区别
/* put_jpeg_yuv420p_memory converts an input image in the YUV420P format into a jpeg image and puts
 * it in a memory buffer.
 * Inputs:
 * - input_image is the image in YUV420P format.
 * - width and height are the dimensions of the image
 * Output:
 * - dest_image is a pointer to the jpeg image buffer
 * Returns buffer size of jpeg image     
 */
static int put_jpeg_yuv420p_memory(unsigned char *dest_image,
                                   unsigned char *input_image, int width, int height)
{
    int i, j, jpeg_image_size;
  
    JSAMPROW y[16],cb[16],cr[16]; // y[2][5] = color sample of row 2 and pixel column 5; (one plane)
    JSAMPARRAY data[3]; // t[0][2][5] = color sample 0 of row 2 and column 5
  
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
  	char *pbuf = NULL;
	int jpglen = 0;
    data[0] = y;
    data[1] = cb;
    data[2] = cr;
  
    cinfo.err = jpeg_std_error(&jerr);  // errors get written to stderr 
      
    jpeg_create_compress(&cinfo);
    cinfo.image_width = width;
    cinfo.image_height = height;
    cinfo.input_components = 3;
    jpeg_set_defaults (&cinfo);
  
    jpeg_set_colorspace(&cinfo, JCS_YCbCr);
  
    cinfo.raw_data_in = TRUE;                  // supply downsampled data
    cinfo.do_fancy_downsampling = FALSE;       // fix segfaulst with v7
    cinfo.comp_info[0].h_samp_factor = 2;
    cinfo.comp_info[0].v_samp_factor = 2;
    cinfo.comp_info[1].h_samp_factor = 1;
    cinfo.comp_info[1].v_samp_factor = 1;
    cinfo.comp_info[2].h_samp_factor = 1;
    cinfo.comp_info[2].v_samp_factor = 1;
  
    jpeg_set_quality(&cinfo, 80, TRUE);
    cinfo.dct_method = JDCT_FASTEST;
  
    jpeg_mem_dest(&cinfo, &pbuf, &jpglen);    // data written to mem
      
    jpeg_start_compress (&cinfo, TRUE);
  
    for (j = 0; j < height; j += 16) {
        for (i = 0; i < 16; i++) {
            y[i] = input_image + width * (i + j);
            if (i%2 == 0) {
                cb[i/2] = input_image + width * height + width / 2 * ((i + j) / 2);
                cr[i/2] = input_image + width * height + width * height / 4 + width / 2 * ((i + j) / 2);
            }
        }
        jpeg_write_raw_data(&cinfo, data, 16);
    }
  
    jpeg_finish_compress(&cinfo);
    jpeg_destroy_compress(&cinfo);
    memcpy(dest_image,pbuf,jpglen);
	if(pbuf)
		free(pbuf);
    return jpglen;
}
最近比较迷茫　所以没有深入研究这些　同时我也一直在想　有些东西到底有没有深入研究的必要　纠结　接下来接着准备看下ffmpeg h264压缩