ffmpeg使用三：ffempg录屏编码rtmp推流
上两篇分别完成对录屏数据保存yuv420p和对yuvp420p的264编码，都保存为文件。
在实际应用中并不需要对其进行保存，而是直接推流到流媒体服务器。本篇主要在上一节264编码的基础上实现推流。
推流非常简单，只需把上一张的输出到文件，改为输出到流媒体服务器的url即可。另外需要注意rtmp推流支持flv封装格式，所以在初始化AVFormatContext的时候用函数avformat_alloc_output_context2()初始化，指定其封装格式。且在编码时一定要写pts。
代码如下：基本跟编码一致
#include
using namespace std;
#include
#define __STDC_CONSTANT_MACROS
//Linux...
extern "C"
{
#include
#include
#include
#include
#include
#include
} int main(int argc, char* argv[]) { AVFormatContext* pInputFormatContext=NULL; AVCodec* pInputCodec=NULL; AVCodecContext* pInputCodecContex=NULL; AVFormatContext *pOutputFormatContext=NULL; AVCodecContext* pOutCodecContext=NULL; AVCodec* pOutCodec=NULL; AVStream* pOutStream=NULL; av_register_all(); avformat_network_init(); avdevice_register_all(); const char* out_file = "rtmp://192.168.80.31:8811/myapp/test6"; int ret,i; int videoindex=-1; //输入（Input） pInputFormatContext = avformat_alloc_context(); AVDictionary* options = NULL; AVInputFormat *ifmt=av_find_input_format("x11grab"); av_dict_set(&options,"framerate","25",0); //av_dict_set(&options,"video_size","1440x900",0); if(avformat_open_input(&pInputFormatContext,":0.0",ifmt,&options)!=0){ //Grab at position 10,20 真正的打开文件,这个函数读取文件的头部并且把信息保存到我们给的AVFormatContext结构体中 printf("Couldn't open input stream.\n"); return -1; } if ((ret = avformat_find_stream_info(pInputFormatContext, 0)) < 0) { printf( "Failed to retrieve input stream information"); return -1; } for(i=0; i
nb_streams; i++) if(pInputFormatContext->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){ videoindex=i; break; } pInputCodecContex=pInputFormatContext->streams[videoindex]->codec;// 相当于虚基类,具体参数流中关于编解码器的信息就是被我们叫做"codec context"（编解码器上下文）的东西。 pInputCodec=avcodec_find_decoder(pInputCodecContex->codec_id);//这里面包含了流中所使用的关于编解码器的所有信息，现在我们有了一个指向他的指针。但是我们必需要找到真正的编解码器并且打开 if(pInputCodec==NULL) { printf("Codec not found.\n"); return -1; } //打开解码器 if(avcodec_open2(pInputCodecContex, pInputCodec,NULL)<0) { printf("Could not open codec.\n"); return -1; } //为一帧图像分配内存 AVFrame *pFrame; AVFrame *pFrameYUV; pFrame=av_frame_alloc(); pFrameYUV=av_frame_alloc();//为转换来申请一帧的内存(把原始帧->YUV) pFrameYUV->format=AV_PIX_FMT_YUV420P; pFrameYUV->width=pInputCodecContex->width; pFrameYUV->height=pInputCodecContex->height; unsigned char *out_buffer=(unsigned char *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pInputCodecContex->width, pInputCodecContex->height)); //现在我们使用avpicture_fill来把帧和我们新申请的内存来结合 avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P, pInputCodecContex->width, pInputCodecContex->height); struct SwsContext *img_convert_ctx; img_convert_ctx = sws_getContext(pInputCodecContex->width, pInputCodecContex->height, pInputCodecContex->pix_fmt, pInputCodecContex->width, pInputCodecContex->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); //============================================================================================= avformat_alloc_output_context2(&pOutputFormatContext, NULL, "flv", out_file); //RTMP if (!pOutputFormatContext) { printf( "Could not create output context\n"); ret = AVERROR_UNKNOWN; return -1; } //Open output URL 打开输入文件 返回AVIOContext(pFormatCtx->pb) if (avio_open(&pOutputFormatContext->pb,out_file, AVIO_FLAG_READ_WRITE) < 0){ printf("Failed to open output file! \n"); return -1; } //创建输出流,AVStream 与 AVCodecContext一一对应 pOutStream = avformat_new_stream(pOutputFormatContext, 0); if(pOutStream == NULL) { printf("Failed create pOutStream!\n"); return -1; } //相当于虚基类,具体参数 pOutCodecContext = pOutStream->codec; pOutCodecContext->codec_id = AV_CODEC_ID_H264; //type pOutCodecContext->codec_type = AVMEDIA_TYPE_VIDEO; //像素格式, pOutCodecContext->pix_fmt = AV_PIX_FMT_YUV420P; //size pOutCodecContext->width = pInputCodecContex->width; pOutCodecContext->height = pInputCodecContex->height; //目标码率 pOutCodecContext->bit_rate = 400000; //每250帧插入一个I帧,I帧越小视频越小 pOutCodecContext->gop_size=100; //Optional Param B帧 pOutCodecContext->max_b_frames=3; pOutCodecContext->time_base.num = 1; pOutCodecContext->time_base.den = 25; pOutCodecContext->lmin=1; pOutCodecContext->lmax=50; //最大和最小量化系数 pOutCodecContext->qmin = 10; pOutCodecContext->qmax = 51; pOutCodecContext->qblur=0.0; av_dump_format(pOutputFormatContext, 0, out_file, 1); AVDictionary *param = 0; // //H.264 if(pOutCodecContext->codec_id == AV_CODEC_ID_H264) { av_dict_set(¶m, "preset", "slow", 0); av_dict_set(¶m, "tune", "zerolatency", 0); } // av_dump_format(pOutputFormatContext, 0, out_file, 1); pOutCodec = avcodec_find_encoder(pOutCodecContext->codec_id); if (!pOutCodec){ printf("Can not find encoder! \n"); return -1; } if (avcodec_open2(pOutCodecContext, pOutCodec,¶m) < 0) { printf("Failed to open encoder! \n"); return -1; } //Write File Header int r = avformat_write_header(pOutputFormatContext,NULL); if(r<0) { printf("Failed write header!\n"); return -1; } AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket)); int got_picture; AVPacket pkt; int picture_size = avpicture_get_size(pOutCodecContext->pix_fmt, pOutCodecContext->width, pOutCodecContext->height); av_new_packet(&pkt,picture_size); int frame_index=0; while((av_read_frame(pInputFormatContext, packet))>=0) { if(packet->stream_index==videoindex) { //真正解码,packet to pFrame avcodec_decode_video2(pInputCodecContex, pFrame, &got_picture, packet); if(got_picture) { sws_scale(img_convert_ctx, (const unsigned char* const*)pFrame->data, pFrame->linesize, 0, pInputCodecContex->height, pFrameYUV->data, pFrameYUV->linesize); pFrameYUV->pts=frame_index; frame_index++; int picture; //真正编码 int ret=avcodec_encode_video2(pOutCodecContext, &pkt,pFrameYUV, &picture); if(ret < 0){ printf("Failed to encode! \n"); return -1; } if (picture==1) { ret = av_interleaved_write_frame(pOutputFormatContext, &pkt); if (ret < 0) { printf( "Error muxing packet\n"); break; } av_free_packet(&pkt); } } } av_free_packet(packet); } //Write file trailer av_write_trailer(pOutputFormatContext); sws_freeContext(img_convert_ctx); //fclose(fp_yuv); av_free(out_buffer); av_free(pFrameYUV); av_free(pFrame); avcodec_close(pInputCodecContex); avformat_close_input(&pInputFormatContext); avcodec_close(pOutStream->codec); av_free(pOutCodec); avcodec_close(pOutCodecContext); avformat_free_context(pOutputFormatContext); return 0; }
基本和上一节的输出到文件的代码一致：
区别一：输出不是重定向到文件，而是一个url；
区别二：初始化输出AVFormatContext所用的函数不一样；
另：关于pts和dts，输出到文件可不设置pts，推流的话，必须设置pts，不然播放器无法播放；若无B帧，pts和dts可设置相等；因为只是实现录屏，并不考虑声音，不用做音视频同步，故只要用pts对每帧进行排序即可。最后会在此基础上实现直播，到时再研究。