rgb32 to i420/yv12

gistfile1.txt

int rgb32_to_i420(int width, int height, const char * src, char * dst)
{
	unsigned char * dst_y_even;
	unsigned char * dst_y_odd;
	unsigned char * dst_u;
	unsigned char * dst_v;
	const unsigned char *src_even;
	const unsigned char *src_odd;
	int i, j;

	src_even = (const unsigned char *)src;
	src_odd = src_even + width * 4;

	// it's planar

	dst_y_even = (unsigned char *) dst;
	dst_y_odd = dst_y_even + width;
	dst_u = dst_y_even + width * height;
	dst_v = dst_u + ((width * height) >> 2);

	// NB this doesn't work perfectly for u and v values of the edges of the video if your video size is not divisible by 2. FWIW.
	for ( i = 0; i < height / 2; ++i )
	{
		for ( j = 0; j < width / 2; ++j )
		{
			short r, g, b;
			b = *src_even++;
			g = *src_even++;
			r = *src_even++;
			++src_even;
			*dst_y_even++ = (( r * 66 + g * 129 + b * 25 + 128 ) >> 8 ) + 16;
			short sum_r = r, sum_g = g, sum_b = b;

			b = *src_even++;
			g = *src_even++;
			r = *src_even++;
			++src_even;
			*dst_y_even++ = (( r * 66 + g * 129 + b * 25 + 128 ) >> 8 ) + 16;
			sum_r += r;
			sum_g += g;
			sum_b += b;

			b = *src_odd++;
			g = *src_odd++;
			r = *src_odd++;
			++src_odd;
			*dst_y_odd++ = (( r * 66 + g * 129 + b * 25 + 128 ) >> 8 ) + 16;
			sum_r += r;
			sum_g += g;
			sum_b += b;

			b = *src_odd++;
			g = *src_odd++;
			r = *src_odd++;
			++src_odd;
			*dst_y_odd++ = (( r * 66 + g * 129 + b * 25 + 128 ) >> 8 ) + 16;
			sum_r += r;
			sum_g += g;
			sum_b += b;

			// compute ave's of this 2x2 bloc for us and v
			// could use Catmull-Rom interpolation maybe?
			sum_r += 2;
			sum_g += 2;
			sum_b += 2;

			sum_r /= 4;
			sum_g /= 4;
			sum_b /= 4;

			*dst_u++ = (( sum_r * -38 - sum_g * 74 + sum_b * 112 + 128 ) >> 8 ) + 128; // only one
			*dst_v++ = (( sum_r * 112 - sum_g * 94 - sum_b * 18 + 128 ) >> 8 ) + 128; // only one
		}

		dst_y_even += width;
		dst_y_odd += width;
		src_even += width * 4;
		src_odd += width * 4;
	}

	return 0;
}