文本主要讲述windows系统下如何利用ffmpeg获取摄像机流并推送到rtmp服务,命令的用法前文
中有讲到过，这次是通过代码来实现。实现该项功能的基本流程如下：
图1 ffmpeg推流流程图
较前面的文章的流程图而言，本流程图显的复杂些，稍微解释下：
ffmpeg 打开摄像头跟打开普通的视频流方法一致，只是输入url是摄像头的名称。真正打开
摄像头操作由dshow来完成，ffmpeg只是调用dshow相应的接口获取返回值；读取packet
的API 依然是av_read_frame,返回的packet并不是编码后的视频包而是原始的图片帧,图片
帧的格式是YUV422(我测试的机器是这样的)。拿到图片帧后并不能直接编码，需要做格式转换
因为libx264不支持YUV422,所以有了上图中的格式转换这一环节。转换图片帧格式后将视频数据
丢给编码器就行编码，编码的packet才可以写到输出流中。
下面给出代码：
1.初始化Ffmpeg
void Init()
{
av_register_all();
avfilter_register_all();
avformat_network_init();
avdevice_register_all();
av_log_set_level(AV_LOG_ERROR);
}
2.创建输入上下文，打开摄像头
int OpenInput(char *fileName)
{
context = avformat_alloc_context();
context->interrupt_callback.callback = interrupt_cb;
AVInputFormat *ifmt = av_find_input_format("dshow");
AVDictionary *format_opts = nullptr;
av_dict_set_int(&format_opts, "rtbufsize", 18432000 , 0);
int ret = avformat_open_input(&context, fileName, ifmt, &format_opts);
if(ret < 0)
{
return ret;
}
ret = avformat_find_stream_info(context,nullptr);
av_dump_format(context, 0, fileName, 0);
if(ret >= 0)
{
cout <<"open input stream successfully" << endl;
}
return ret;
}
3. 初始化编码器
int InitOutputCodec(AVCodecContext** pOutPutEncContext, int iWidth, int iHeight)
{
AVCodec * pH264Codec = avcodec_find_encoder(AV_CODEC_ID_H264);
if(NULL == pH264Codec)
{
printf("%s", "avcodec_find_encoder failed");
return 0;
}
*pOutPutEncContext = avcodec_alloc_context3(pH264Codec);
(*pOutPutEncContext)->codec_id = pH264Codec->id;
(*pOutPutEncContext)->time_base.num =0;
(*pOutPutEncContext)->time_base.den = 1;
(*pOutPutEncContext)->pix_fmt = AV_PIX_FMT_YUV420P;
(*pOutPutEncContext)->width = iWidth;
(*pOutPutEncContext)->height = iHeight;
(*pOutPutEncContext)->has_b_frames = 0;
(*pOutPutEncContext)->max_b_frames = 0; AVDictionary *options = nullptr;
(*pOutPutEncContext)->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
int ret = avcodec_open2(*pOutPutEncContext, pH264Codec, &options);
if (ret < 0)
{
printf("%s", "open codec failed");
return ret;
}
return 1;
}
4.创建输出上下文以及输出流
int OpenOutput(char *fileName)
{
int ret = 0;
ret = avformat_alloc_output_context2(&outputContext, nullptr, "flv", fileName);
if(ret < 0)
{
goto Error;
}
ret = avio_open2(&outputContext->pb, fileName, AVIO_FLAG_READ_WRITE,nullptr, nullptr);
if(ret < 0)
{
goto Error;
} for(int i = 0; i < context->nb_streams; i++)
{
AVStream * stream = avformat_new_stream(outputContext, pOutPutEncContext->codec);
stream->codec = pOutPutEncContext;
if(ret < 0)
{
goto Error;
}
}
av_dump_format(outputContext, 0, fileName, 1);
ret = avformat_write_header(outputContext, nullptr);
if(ret < 0)
{
goto Error;
}
if(ret >= 0)
cout <<"open output stream successfully" << endl;
return ret ;
Error:
if(outputContext)
{
for(int i = 0; i < outputContext->nb_streams; i++)
{
avcodec_close(outputContext->streams[i]->codec);
}
avformat_close_input(&outputContext);
}
return ret ;
}
4.从输入流读取视频包
std::shared_ptr<AVPacket> ReadPacketFromSource()
{
std::shared_ptr<AVPacket> packet(static_cast<AVPacket*>(av_malloc(sizeof(AVPacket))), [&](AVPacket *p) { av_packet_free(&p); av_freep(&p); });
av_init_packet(packet.get());
lastFrameRealtime = av_gettime();
int ret = av_read_frame(context, packet.get());
if(ret >= 0)
{
return packet;
}
else
{
return nullptr;
}
}
5.格式转换
int YUV422To420(uint8_t *yuv422, uint8_t *yuv420, int width, int height)
{
int s = width * height;
int i,j,k = 0;
for(i = 0; i < s;i++)
{
yuv420[i] = yuv422[i * 2];
} for(i = 0; i < height; i++)
{
if(i%2 != 0) continue;
for(j = 0; j <(width /2); j++)
{
if(4 * j + 1 > 2 * width) break;
yuv420[s + k * 2 * width / 4 +j] = yuv422[i * 2 * width + 4 *j + 1];
}
k++;
} k = 0; for(i = 0; i < height; i++)
{
if(i % 2 == 0) continue;
for(j = 0; j < width / 2; j++)
{
if(4 * j + 3 > 2 * width) break;
yuv420[s + s / 4 + k * 2 *width / 4 + j] = yuv422[i *2 * width + 4 * j + 3];
}
k++;
}
return 1;
};
6. 简单实例
string fileInput="video=Integrated Webcam";
string fileOutput="rtmp://127.0.0.1/live/mystream"; Init();
if(OpenInput((char *)fileInput.c_str()) < 0)
{
cout << "Open file Input failed!" << endl;
this_thread::sleep_for(chrono::seconds(10));
return 0;
}
InitOutputCodec(&pOutPutEncContext,DstWidth,DstHeight);
if(OpenOutput((char *)fileOutput.c_str()) < 0)
{
cout << "Open file Output failed!" << endl;
this_thread::sleep_for(chrono::seconds(10));
return 0;
}
auto timebase = av_q2d(context->streams[0]->time_base);
int count = 0;
auto in_stream = context->streams[0];
auto out_stream = outputContext->streams[0];
int iGetPic = 0;
uint8_t *yuv420Buffer = (uint8_t *)malloc(DstWidth * DstHeight * 3 / 2);
yuv420Buffer[DstWidth * DstHeight * 3 / 2 - 1] = 0;
while(true)
{
auto packet = ReadPacketFromSource();
if(packet)
{
auto pSwsFrame = av_frame_alloc();
int numBytes=av_image_get_buffer_size(AV_PIX_FMT_YUYV422, DstWidth, DstHeight, 1);
YUV422To420(packet->data, yuv420Buffer, DstWidth, DstHeight);
av_image_fill_arrays((pSwsFrame)->data, (pSwsFrame)->linesize, yuv420Buffer, AV_PIX_FMT_YUV420P, DstWidth, DstHeight, 1);
AVPacket *pTmpPkt = (AVPacket *)av_malloc(sizeof(AVPacket));
av_init_packet(pTmpPkt);
pTmpPkt->data = NULL;
pTmpPkt->size = 0; int iRet = avcodec_encode_video2(pOutPutEncContext, pTmpPkt, pSwsFrame, &iGetPic);
if(iRet >= 0 && iGetPic)
{
int ret = av_write_frame(outputContext, pTmpPkt);
cout << "ret:"<< ret <<endl;
//this_thread::sleep_for(std::chrono::milliseconds(40));
}
av_frame_free(&pSwsFrame);
av_packet_free(&pTmpPkt);
}
}
CloseInput();
CloseOutput();
cout <<"Transcode file end!" << endl;
this_thread::sleep_for(chrono::hours(10));
return 0;
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