windows ffmpeg 推送攝像頭數據到rtmp服務

文本主要講述windows系統下如何利用ffmpeg獲取攝像機流並推送到rtmp服務,命令的用法前文

中有講到過，這次是通過代碼來實現。實現該項功能的基本流程如下：

                 圖1 ffmpeg推流流程圖

較前面的文章的流程圖而言，本流程圖顯的復雜些，稍微解釋下：

ffmpeg 打開攝像頭跟打開普通的視頻流方法一致，只是輸入url是攝像頭的名稱。真正打開

攝像頭操作由dshow來完成，ffmpeg只是調用dshow相應的接口獲取返回值；讀取packet

的API 依然是av_read_frame,返回的packet並不是編碼后的視頻包而是原始的圖片幀,圖片

幀的格式是YUV422(我測試的機器是這樣的)。拿到圖片幀后並不能直接編碼，需要做格式轉換

因為libx264不支持YUV422,所以有了上圖中的格式轉換這一環節。轉換圖片幀格式后將視頻數據

丟給編碼器就行編碼，編碼的packet才可以寫到輸出流中。

下面給出代碼：

  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.創建輸入上下文，打開攝像頭

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. 初始化編碼器

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.創建輸出上下文以及輸出流

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.從輸入流讀取視頻包

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.格式轉換

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. 簡單實例

	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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