场景：
安卓摄像头获取画面的处理。

内容来自：
https://code.google.com/p/libyuv

源代码下载：
http://files.cnblogs.com/files/wzswzd/libyuv-master.zip

相关的代码如下：

#define YG 18997 /* round(1.164 * 64 * 256 * 256 / 257) */
#define YGB -1160 /* 1.164 * 64 * -16 + 64 / 2 */

#define UB -128 /* max(-128, round(-2.018 * 64)) */
#define UG 25 /* round(0.391 * 64) */
#define VG 52 /* round(0.813 * 64) */
#define VR -102 /* round(-1.596 * 64) */

#define BB (UB * 128            + YGB)
#define BG (UG * 128 + VG * 128 + YGB)
#define BR            (VR * 128 + YGB)

typedef unsigned char sd_uint8;
typedef unsigned long sd_uint32;
typedef signed long sd_int32;

sd_int32 clamp0(sd_int32 v) { return ((-(v) >> 31) & (v)); }
sd_int32 clamp255(sd_int32 v) { return (((255 - (v)) >> 31) | (v)) & 255; }
sd_uint32 Clamp(sd_int32 val) { int v = clamp0(val); return (sd_uint32)(clamp255(v)); }

void YuvPixel(
    sd_uint8 y,
    sd_uint8 u,
    sd_uint8 v,
    sd_uint8* b,
    sd_uint8* g,
    sd_uint8* r
    ){
    sd_uint32 y1 = (sd_uint32)(y * 0x0101 * YG) >> 16;
    *r = Clamp((sd_int32)(-(u * UB) + y1 + BB) >> 6);
    *g = Clamp((sd_int32)(-(v * VG + u * UG) + y1 + BG) >> 6);
    *b = Clamp((sd_int32)(-(v * VR) + y1 + BR) >> 6);
}
void NV21ToARGBRow_C(
    const sd_uint8* src_y,
    const sd_uint8* src_vu,
    sd_uint8* rgb_buf,
    int width
    ){
    int x;
    for ( x = 0; x < width - 1; x += 2 ) {
        YuvPixel(src_y[0], src_vu[1], src_vu[0], rgb_buf + 0, rgb_buf + 1, rgb_buf + 2);
        rgb_buf[3] = 255;
        YuvPixel(src_y[1], src_vu[1], src_vu[0], rgb_buf + 4, rgb_buf + 5, rgb_buf + 6);
        rgb_buf[7] = 255;
        src_y += 2;
        src_vu += 2;
        rgb_buf += 8;
    }
    if ( width & 1 ) {
        YuvPixel(src_y[0], src_vu[1], src_vu[0], rgb_buf + 0, rgb_buf + 1, rgb_buf + 2);
        rgb_buf[3] = 255;
    }
}
int NV21ToARGB(
    const sd_uint8* src_y,
    int src_stride_y,
    const sd_uint8* src_uv,
    int src_stride_uv,
    sd_uint8* dst_argb,
    int dst_stride_argb,
    int width,
    int height
    ){
    int y;
    if ( !src_y || !src_uv || !dst_argb || width <= 0 || height == 0 ) { return -1; }
    for ( y = 0; y < height; ++y ) {
        NV21ToARGBRow_C(src_y, src_uv, dst_argb, width);
        dst_argb += dst_stride_argb;
        src_y += src_stride_y;
        if ( y & 1 ) {
            src_uv += src_stride_uv;
        }
    }
    return 0;
}
int ConvertToARGB(
    const sd_uint8* sample, // 原图的地址
    sd_uint8* crop_argb, // RGBA的地址
    int argb_stride, //  should be width * 4 or width must be 1 right
    int crop_x, // 裁剪的x坐标
    int crop_y, // 裁剪的y坐标
    int src_width, // 原图的宽度
    int src_height, // 原图的高度
    int crop_width, // 裁剪的宽度
    int crop_height // 裁剪的高度
    ){
    const sd_uint8* src;
    const sd_uint8* src_uv;
    int aligned_src_width = (src_width + 1) & ~1;
    src = sample + (src_width * crop_y + crop_x);
    src_uv = sample + aligned_src_width * (src_height + crop_y / 2) + crop_x;
    // Call NV12 but with u and v parameters swapped.
    return NV21ToARGB(src, src_width, src_uv, aligned_src_width, crop_argb, argb_stride, crop_width, crop_height);
}