尝试使用C语言将YUV420p转换为RGBA

Question

我的视频数据是YUV420p（I420）。我尝试使用C语言转换为RGBA，但我不知道我的代码的哪一部分是错误的，我无法获得正确的RGBA数据。

const void *data = [frameData bytes];

NSInteger numOfPixel = width * height;
NSInteger positionOfV = numOfPixel;
NSInteger positionOfU = numOfPixel * 5 / 4;
uint8_t *rgba = malloc(numOfPixel * 4);

for (uint32_t i = 0; i < height; i ++) {
    NSInteger startY = i * width;
    NSInteger step = (i/2)*(width/2);
    NSInteger startU = positionOfU + step;
    NSInteger startV = positionOfV + step;

    for (uint32_t j = 0; j < width; j ++) {
        NSInteger indexY = startY + j;
        NSInteger indexU = startU + j/2;
        NSInteger indexV = startV + j/2;
        NSInteger index = indexY * 4;

        uint8_t Y = *(uint8_t *)(&data[indexY]);
        uint8_t U = *(uint8_t *)(&data[indexU]);
        uint8_t V = *(uint8_t *)(&data[indexV]);

        int r = (int)((Y&0xff) + 1.4075 * ((V&0xff) - 128));
        int g = (int)((Y&0xff) - 0.3455 * ((U&0xff)-128) - 0.7169*((V&0xff)-128));
        int b = (int)((Y&0xff) + 1.779 * ((U&0xff)-128));
        int a = 0xff;

        if (r<0) r=0; if (r>255) r=255;
        if (g<0) g=0; if (g>255) g=255;
        if (b<0) b=0; if (b>255) b=255;

        rgba[index] = (uint8_t)r;
        rgba[index + 1] = (uint8_t)g;
        rgba[index + 2] = (uint8_t)b;
        rgba[index + 3] = (uint8_t)a;
    }
}