使用c语言和jpeg库实现将jpeg图片转成NV21格式的yuv数据

要将JPEG图片转换为NV21格式的YUV数据，需要使用libjpeg库解码JPEG图片，然后使用YUV转换算法将RGB数据转换为YUV格式。以下是一个使用C语言和libjpeg库实现此功能的示例程序：

#include <stdio.h>
#include <stdlib.h>
#include <jpeglib.h>

#define YUV420P_PIXEL_SIZE 3
#define RGB_PIXEL_SIZE 3

int main(int argc, char** argv) {
    if (argc != 3) {
        printf("Usage: jpeg2nv21 <input_file> <output_file>\n");
        return 0;
    }

    char* input_file = argv[1];
    char* output_file = argv[2];

    // Open input file
    FILE* infile = fopen(input_file, "rb");
    if (infile == NULL) {
        printf("Could not open input file: %s\n", input_file);
        return 0;
    }

    // Initialize libjpeg structures
    struct jpeg_decompress_struct cinfo;
    struct jpeg_error_mgr jerr;
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_decompress(&cinfo);
    jpeg_stdio_src(&cinfo, infile);

    // Read JPEG header
    jpeg_read_header(&cinfo, TRUE);

    // Start decompression
    jpeg_start_decompress(&cinfo);

    // Allocate memory for RGB buffer
    int row_stride = cinfo.output_width * RGB_PIXEL_SIZE;
    JSAMPARRAY buffer = (*cinfo.mem->alloc_sarray)
        ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
    int rgb_size = cinfo.output_width * cinfo.output_height * RGB_PIXEL_SIZE;
    unsigned char* rgb_data = (unsigned char*) malloc(rgb_size);

    // Read RGB data
    int row_index = 0;
    while (cinfo.output_scanline < cinfo.output_height) {
        jpeg_read_scanlines(&cinfo, buffer, 1);
        memcpy(rgb_data + row_index * row_stride, buffer[0], row_stride);
        row_index++;
    }

    // Finish decompression
    jpeg_finish_decompress(&cinfo);
    jpeg_destroy_decompress(&cinfo);
    fclose(infile);

    // Convert RGB to NV21
    int y_size = cinfo.output_width * cinfo.output_height;
    int uv_size = y_size / 2;
    unsigned char* nv21_data = (unsigned char*) malloc(y_size + uv_size);

    int y_index = 0;
    int uv_index = 0;
    for (int i = 0; i < rgb_size; i += RGB_PIXEL_SIZE) {
        int r = rgb_data[i];
        int g = rgb_data[i + 1];
        int b = rgb_data[i + 2];

        // Convert RGB to YUV
        int y = (int) (0.299 * r + 0.587 * g + 0.114 * b);
        int u = (int) (-0.169 * r - 0.331 * g + 0.5 * b + 128);
        int v = (int) (0.5 * r - 0.419 * g - 0.081 * b + 128);

        // Write Y data
        nv21_data[y_index] = (unsigned char) y;
        y_index++;

        // Write UV data
        if (i % (2 * RGB_PIXEL_SIZE) == 0) {
            nv21_data[y_size + uv_index] = (unsigned char) v;
            nv21_data[y_size + uv_size + uv_index] = (unsigned char) u;
            uv_index++;
        }
    }

    // Write NV21 data to output file
    FILE* outfile = fopen(output_file, "wb");
    if (outfile == NULL) {
        printf("Could not open output file: %s\n", output_file);
        return 0;
    }
    fwrite(nv21_data, 1, y_size + uv_size, outfile);
    fclose(outfile);

    // Free memory
    free(rgb_data);
    free(nv21_data);

    return 0;
}

注意，这是一个简单的示例程序，可能需要根据具体需求进行修改。在使用此程序时，需要将libjpeg库链接到编译命令中。具体方法可以参考libjpeg库的说明文档。