最近整理之前代码，发现之前写过一个利用jpeg库将 yuv420p/yuv444p转为指定大小的jpeg格式图片的代码，共享出来供小伙伴们参考。

JmJpegHelper.h

//
//Created by Jimmy.Wei on 2018-02-13
//
#ifndef _JPEG_HELPER_H_
#define _JPEG_HELPER_H_#include <stdlib.h>
//
//Created by Jimmy.Wei
//
#include <stddef.h>
#include <stdio.h>
#include <string.h>#include <libjpeg/jpeglib.h>#define DEFAULT_JPEG_QUAULITY 50typedef struct _JmYuv{unsigned char *yPtr;unsigned char *uPtr;unsigned char *vPtr;int width;int height;int stride;int stride1;int stride2;bool is420p;//true:420p,false:444p
} JmYuv;class JmJpegHelper{
public:JmJpegHelper(): jpeg_buf_(nullptr), jpeg_size_(0){}virtual ~JmJpegHelper(){}//the returned poniter must be called freeJpeg() or free manually by yourself after usedunsigned char *PlanarYuv2JpegEncoder(unsigned long &out_size, JmYuv *yuv, int quality);void freeJpeg();protected:private:unsigned long yuv2jpeg(unsigned char **dest_image, JmYuv *yuv, int quality);void jmCompress(j_compress_ptr cinfo, JmYuv *yuv);unsigned char *jpeg_buf_;unsigned long jpeg_size_;
};#endif //_JPEG_HELPER_H_

JmJpegHelper.cpp

//
//Created by Jimmy.Wei on 2018-02-13
//
#include "JmJpegHelper.h"unsigned char *JmJpegHelper::PlanarYuv2JpegEncoder(unsigned long &out_size, JmYuv *yuv, int quality)
{out_size = yuv2jpeg(&jpeg_buf_, yuv, quality);return jpeg_buf_;
}void JmJpegHelper::freeJpeg()
{if(jpeg_buf_) {free(jpeg_buf_);jpeg_buf_ = nullptr;jpeg_size_ = 0;printf("after free\n");}
}unsigned long JmJpegHelper::yuv2jpeg(unsigned char **dest_image, JmYuv *yuv, int quality)
{(*dest_image) = nullptr;if (!yuv || !(yuv->yPtr) || !(yuv->uPtr) || !(yuv->vPtr))return 0;if (yuv->width <=0 || yuv->height <= 0)return 0;int width = yuv->width;int height = yuv->height;struct jpeg_compress_struct cinfo;// = {0};struct jpeg_error_mgr jerr;// = {0};cinfo.err = jpeg_std_error(&jerr);  // errors get written to stderrjpeg_create_compress(&cinfo);cinfo.image_width = width;cinfo.image_height = height;cinfo.input_components = 3;cinfo.in_color_space = JCS_YCbCr;jpeg_set_defaults(&cinfo);jpeg_set_colorspace(&cinfo, JCS_YCbCr);cinfo.raw_data_in = yuv->is420p?TRUE:FALSE;                  // supply downsampled data
//    cinfo.do_fancy_downsampling = FALSE;       // fix segfaulst with v7cinfo.comp_info[0].h_samp_factor = 2;cinfo.comp_info[0].v_samp_factor = 2;
#if 0cinfo.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;
#endifjpeg_set_quality(&cinfo, quality, TRUE);cinfo.optimize_coding = TRUE;cinfo.dct_method = JDCT_FASTEST;//    jpeg_mem_dest(&cinfo, dest_image, width * height * 2);    // data written to memunsigned long jpeg_image_size = 0;jpeg_mem_dest(&cinfo, dest_image, &jpeg_image_size);    // data written to memjpeg_start_compress(&cinfo, TRUE);jmCompress(&cinfo, yuv);//compress to jpegjpeg_finish_compress(&cinfo);
//    jpeg_image_size = jpeg_mem_size(&cinfo);jpeg_destroy_compress(&cinfo);return jpeg_image_size;
}void JmJpegHelper::jmCompress(j_compress_ptr cinfo, JmYuv *yuv)
{unsigned char *yPtr = yuv->yPtr;unsigned char *uPtr = yuv->uPtr;unsigned char *vPtr = yuv->vPtr;int width = yuv->width;int height = yuv->height;int stride = yuv->stride;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 5data[0] = y;data[1] = cb;data[2] = cr;//    printf("before compress time: %s\n", getNow(NOW_BUFF));int i, j;if (yuv->is420p) {int uv_stride = yuv->stride1;//or yuv->stride2;for (j = 0; j < height; j += 16) {for (i = 0; i < 16; i++) {y[i] = yPtr + stride * (i+j);if (i%2 == 0){cb[i/2] = uPtr + uv_stride * ((i + j) / 2);//uPtr + width / 2 * ((i + j) / 2);cr[i/2] = vPtr + uv_stride * ((i + j) / 2);//vPtr + width / 2 * ((i + j) / 2);}}jpeg_write_raw_data(cinfo, data, 16);}}else {
#if 0//raw data mode is not support with 444pfor (j = 0; j < height; j += 16) {for (i = 0; i < 16; i++) {y[i] = yPtr + stride * (i+j);cb[i] = uPtr + stride * (i+j);cr[i] = vPtr + stride * (i+j);}jpeg_write_raw_data(cinfo, data, 16);}
#endifJSAMPROW row_pointer[1];unsigned char *yuv_row = (unsigned char *)malloc(width*3);int idx, line = 0;while (cinfo->next_scanline < cinfo->image_height) {idx = 0;for(int i = 0; i < width; i++) {yuv_row[idx++] = yPtr[i + line*stride];//ybase[i + line * image_width];yuv_row[idx++] = uPtr[i + line*stride];//ubase[line/2 * image_width+(i/2)*2]; y[0]u[0]u[1] y[1]u[0]u[1] y[3]u[2]u[3] y[4]u[2]u[3]yuv_row[idx++] = vPtr[i + line*stride];//ubase[line/2 * image_width+(i/2)*2+1]; y[0]u[0]u[1] y[1]u[0]u[1] y[3]u[2]u[3] y[4]u[2]u[3]#if 0//for 420p, but is poor efficiency, compress one frame(1920*1080) large 300usyuv_row[idx++] = uPtr[(line/2)*stride/2 + (i/2)];//ubase[line/2 * image_width+(i/2)*2];yuv_row[idx++] = vPtr[(line/2)*stride/2 + (i/2)];//ubase[line/2 * image_width+(i/2)*2+1];
#endif}row_pointer[0] = yuv_row;jpeg_write_scanlines(cinfo, row_pointer, 1);line++;}free(yuv_row);}//    printf("after compress time: %s\n", getNow(NOW_BUFF));
}

下载链接中为用QT工程的，包括jpeg的头文件， 由于是在aarch64下编译的，所以 其它平台的库文件并未打包进来，大家根据可以找到相应平台的库文件放到相应目录下即可编译使用，main.cpp中有简单使用方法。

下载链接：https://download.csdn.net/download/weizhiming/12541665