H264解码之YUV格式转换及缩放

int video_decoder::swscale(const char* srcbuf, int ntype, int nsrcwidth, int nsrcheight, int ndstwidth, int ndstheight, unsigned char* dstbuf)
{
	if (5 != ntype && 3 != ntype)
	{
		return -1;
	}
	if (!srcbuf || !dstbuf)
		return -1;
	AVPixelFormat srcpixfmt = AV_PIX_FMT_YUV420P;
	AVPixelFormat dstpixfmt = AV_PIX_FMT_BGR32;
	uint8_t* src_y = 0;
	uint8_t* src_u = 0;
	uint8_t* src_v = 0;
	if (3 == ntype)
	{
		src_y = (uint8_t*)srcbuf;
		src_v = (uint8_t*)srcbuf + nsrcwidth * nsrcheight;
		src_u = (uint8_t*)srcbuf + nsrcwidth * nsrcheight + nsrcwidth * nsrcheight / 4;
	}
	else
	{
		src_y = (uint8_t*)srcbuf;
		src_u = (uint8_t*)srcbuf + nsrcwidth * nsrcheight;
		src_v = (uint8_t*)srcbuf + nsrcwidth * nsrcheight + nsrcwidth * nsrcheight / 4;
	}
	uint8_t* src[3] = { src_y, src_v, src_u };
	int srcstride[3] = { nsrcwidth, nsrcwidth / 2, nsrcwidth / 2 };
	srcstride[0] = nsrcwidth;
	srcstride[1] = nsrcwidth / 2;
	srcstride[2] = nsrcwidth / 2;
	src[0] += srcstride[0] * (nsrcheight - 1);
	srcstride[0] *= -1;
	src[1] += srcstride[1] * (nsrcheight / 2 - 1);
	srcstride[1] *= -1;
	src[2] += srcstride[2] * (nsrcheight / 2 - 1);
	srcstride[2] *= -1;

	uint8_t* dst[4] = { dstbuf, NULL, NULL, NULL };
	int dststride[4] = { ndstwidth * 4, 0, 0, 0 };
	SwsContext* s = sws_getContext(nsrcwidth, nsrcheight, srcpixfmt, ndstwidth, ndstheight, dstpixfmt, SWS_BICUBIC, NULL, NULL, NULL);
	if (NULL == s)
	{
		return 0;
	}
	sws_scale(s, src, srcstride, 0, nsrcheight, dst, dststride);
	sws_freeContext(s);
	return 0;
}