整体方案：
采集端：摄像头采集（YUV）->编码（YUV转H264）->RTMP推流
客户端：RTMP拉流->解码（H264转YUV）->YUV显示（SDL2）

H264码流转YUV是视频解码部分，具体的代码实现如下。

#include <stdio.h>
#include <stdlib.h>
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/imgutils.h>
#include <libswscale/swscale.h>
#ifdef __cplusplus
}
#endifint main(int argc, char *argv[])
{char* in_file = NULL;char* out_file = NULL;av_log_set_level(AV_LOG_INFO);if(argc < 3){av_log(NULL, AV_LOG_ERROR, "缺少输入文件和输出文件参数");return -1;}in_file = argv[1];out_file = argv[2];AVFormatContext *fmt_ctx = NULL;AVCodecContext *cod_ctx = NULL;AVCodec *cod = NULL;struct SwsContext *img_convert_ctx = NULL;int ret = 0;AVPacket packet;//第一步创建输入文件AVFormatContextfmt_ctx = avformat_alloc_context();if (fmt_ctx == NULL){ret = -1;av_log(NULL, AV_LOG_ERROR,"alloc fail");goto __ERROR;}if (avformat_open_input(&fmt_ctx, in_file, NULL, NULL) != 0){ret = -1;av_log(NULL, AV_LOG_ERROR,"open fail");goto __ERROR;}//第二步 查找文件相关流，并初始化AVFormatContext中的流信息if (avformat_find_stream_info(fmt_ctx, NULL) < 0){ret = -1;av_log(NULL, AV_LOG_ERROR,"find stream fail");goto __ERROR;}av_dump_format(fmt_ctx, 0, in_file, 0);//第三步查找视频流索引和解码器int stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &cod, -1);//第四步设置解码器上下文并打开解码器AVCodecParameters *codecpar = fmt_ctx->streams[stream_index]->codecpar;if (!cod){ret = -1;av_log(NULL, AV_LOG_ERROR,"find codec fail");goto __ERROR;}cod_ctx = avcodec_alloc_context3(cod);avcodec_parameters_to_context(cod_ctx, codecpar);ret = avcodec_open2(cod_ctx, cod, NULL);if (ret < 0){av_log(NULL, AV_LOG_ERROR,"can't open codec");goto __ERROR;}//第五步打开输出文件FILE *out_fb = NULL;out_fb = fopen(out_file, "wb");if (!out_fb){av_log(NULL, AV_LOG_ERROR,"can't open file");goto __ERROR;}//创建packet,用于存储解码前的数据av_init_packet(&packet);//第六步创建Frame，用于存储解码后的数据AVFrame *frame = av_frame_alloc();frame->width = codecpar->width;frame->height = codecpar->height;frame->format = codecpar->format;av_frame_get_buffer(frame, 32);AVFrame *yuv_frame = av_frame_alloc();yuv_frame->width = codecpar->width;yuv_frame->height = codecpar->height;yuv_frame->format = AV_PIX_FMT_YUV420P;av_frame_get_buffer(yuv_frame, 32);// size_t writesize = av_image_get_buffer_size(frame->format, frame->width,frame->height, 32);//第七步重采样初始化与设置参数// uint8_t **data = (uint8_t **)av_calloc((size_t)out_channels, sizeof(*data))img_convert_ctx = sws_getContext(codecpar->width, codecpar->height, codecpar->format, codecpar->width, codecpar->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);//while循环，每次读取一帧，并转码//第八步 读取数据并解码,重采样进行保存int count = 0;while (av_read_frame(fmt_ctx, &packet) >= 0){if (packet.stream_index != stream_index){av_packet_unref(&packet);continue;}ret = avcodec_send_packet(cod_ctx, &packet);if (ret < 0){ret = -1;av_log(NULL, AV_LOG_ERROR,"decode error");goto __ERROR;}while (avcodec_receive_frame(cod_ctx, frame) >= 0){av_log(NULL, AV_LOG_INFO,"decode frame count = %d\n" , count++);sws_scale(img_convert_ctx,(const uint8_t **)frame->data, frame->linesize,0,codecpar->height, yuv_frame->data,yuv_frame->linesize);int y_size = cod_ctx->width * cod_ctx->height;fwrite(yuv_frame->data[0], 1, y_size, out_fb);fwrite(yuv_frame->data[1], 1, y_size/4, out_fb);fwrite(yuv_frame->data[2], 1, y_size/4, out_fb);}av_packet_unref(&packet);}while(1){av_log(NULL, AV_LOG_INFO,"flush decode \n");ret = avcodec_send_packet(cod_ctx, NULL);if (ret < 0){ret = -1;av_log(NULL, AV_LOG_ERROR,"flush decode error\n");goto __ERROR;}while (avcodec_receive_frame(cod_ctx, frame) >= 0){av_log(NULL, AV_LOG_INFO,"flush decode frame count = %d" , count++);sws_scale(img_convert_ctx,(const uint8_t **)frame->data, frame->linesize,0,codecpar->height, yuv_frame->data,yuv_frame->linesize);int y_size = cod_ctx->width * cod_ctx->height;fwrite(yuv_frame->data[0], 1, y_size, out_fb);fwrite(yuv_frame->data[1], 1, y_size/4, out_fb);fwrite(yuv_frame->data[2], 1, y_size/4, out_fb);}}__ERROR:if (fmt_ctx){avformat_close_input(&fmt_ctx);avformat_free_context(fmt_ctx);}if (cod_ctx){avcodec_close(cod_ctx);avcodec_free_context(&cod_ctx);}if (out_fb){fclose(out_fb);}if (frame){av_frame_free(&frame);}if (yuv_frame){av_frame_free(&yuv_frame);}if(img_convert_ctx){sws_freeContext(img_convert_ctx);}return ret;
}

工程链接：https://download.csdn.net/download/sishen4199/88522521?spm=1001.2014.3001.5503
查看YUV视频的工具：https://download.csdn.net/download/sishen4199/88522520?spm=1001.2014.3001.5503
查看H264码流的工具：https://download.csdn.net/download/sishen4199/88522519?spm=1001.2014.3001.5503