FFmpeg 4.0.2 解码h264为YUV

一、FFmpeg 4.0.2解码h264为YUV的流程如下图所示：

二、C/C++代码：

#include 
extern "C"
{
#include 
#include 
#include 
#include 
#include 
};
using namespace std;

int main()
{
	const char *fname = "test.h264";
	// 打开h264文件，并把文件信息存入fctx中 
	int iRes = 0;
	AVFormatContext *fctx = avformat_alloc_context();
	if ((iRes = avformat_open_input(&fctx, fname, NULL, NULL)) != 0)
	{
		cout << "File open failed!" << endl;
		return -1;
	}
	// 寻找视频流信息
	if (avformat_find_stream_info(fctx, NULL) < 0)
	{
		cout << "Stream find failed!\n";
		return -1;
	}
	// dump调试信息
	av_dump_format(fctx, -1, fname, NULL);
	// 打开了视频并且获取了视频流 ，设置视频索引值默认值
	int vindex = -1;
	for (int i = 0; i < fctx->nb_streams; i++)
	{
		if (fctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
			vindex = i;
	}
	// 如果没有找到视频的索引，说明并不是一个视频文件
	if (vindex == -1)
	{
		cout << "Codec find failed!" << endl;
		return -1;
	}
	// 分配解码器上下文空间
	AVCodecContext *cctx = avcodec_alloc_context3(NULL);
	// 获取编解码器上下文信息
	if (avcodec_parameters_to_context(cctx, fctx->streams[vindex]->codecpar) < 0)
	{
		cout << "Copy stream failed!" << endl;
		return -1;
	}
	// 查找解码器
	AVCodec *c = avcodec_find_decoder(cctx->codec_id);
	if (!c) {
		cout << "Find Decoder failed!" << endl;
		return -1;
	}
	// 打开解码器
	if (avcodec_open2(cctx, c, NULL) != 0) {
		cout << "Open codec failed!" << endl;
		return -1;
	}
	// 对图形进行宽度上方的裁剪，以便于显示得更好
	struct SwsContext *imgCtx = sws_getContext(cctx->width, cctx->height, cctx->pix_fmt, cctx->width, cctx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
	if (!imgCtx) 
	{
		cout << "Get swscale context failed!" << endl;
		return -1;
	}
	AVPacket *pkt = av_packet_alloc();
	AVFrame *fr = av_frame_alloc();
	AVFrame *yuv = av_frame_alloc();
	int vsize = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, cctx->width, cctx->height, 1);
	uint8_t *buf = (uint8_t *)av_malloc(vsize);
	av_image_fill_arrays(yuv->data, yuv->linesize, buf, AV_PIX_FMT_YUV420P, cctx->width, cctx->height, 1);
	char errbuf[256] = { 0 };
	FILE *fp_yuv = fopen("test_out.yuv", "wb+");
	while (av_read_frame(fctx, pkt) >= 0) 
	{
		if (pkt->stream_index == vindex) 
		{
			if ((iRes = avcodec_send_packet(cctx, pkt)) != 0)
			{
				cout << "Send video stream packet failed!" << endl;
				av_strerror(iRes, errbuf, 256);
				return -5;
			}
			if ((iRes = avcodec_receive_frame(cctx, fr)) != 0)
			{
				cout << "Receive video frame failed!" << endl;
				av_strerror(iRes, errbuf, 256);
				return -6;
			}
			cout << "decoding the frame " << cctx->frame_number << endl;
			sws_scale(imgCtx, fr->data, fr->linesize, 0, cctx->height, yuv->data, yuv->linesize);
			int y_size = cctx->width*cctx->height;
			fwrite(yuv->data[0], 1, y_size, fp_yuv);		// Y 
			fwrite(yuv->data[1], 1, y_size / 4, fp_yuv);	// U
			fwrite(yuv->data[2], 1, y_size / 4, fp_yuv);	// V
		}
	}
	av_free(buf);
	av_frame_free(&yuv);
	av_frame_free(&fr);
	av_packet_free(&pkt);
	sws_freeContext(imgCtx);
 	avcodec_free_context(&cctx);
	avformat_close_input(&fctx);
	avformat_free_context(fctx);
    fclose(fp_yuv);// 非常重要
	return getchar();
}

三、新增/替换的API函数
(1) avcodec_parameters_to_context()
(2) av_image_get_buffer_size()
(3) av_image_fill_arrays()
(4) avcodec_send_frame()
(5) avcodec_receive_packet()
(6) av_packet_unref()