Receiving RTSP stream using FFMPEG and OpenCV.md

Receiving RTSP stream using FFMPEG and OpenCV

如果想要用OpenCV接收IPcam的串流來源，其中一種方法可以透過FFMPEG的Library實現。

首先電腦必須安裝FFMPEG

以下是Sample Code：

#include "stdafx.h"
#include <iostream>
#include <opencv2/highgui/highgui.hpp>

extern "C" {
#include <libavutil/opt.h>
#include <libavdevice/avdevice.h>
#include <libswscale/swscale.h>
#include <libavcodec/avcodec.h>
}

#pragma comment(lib, "avcodec.lib")
#pragma comment(lib, "avdevice.lib")
#pragma comment(lib, "avfilter.lib")
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "swscale.lib")

int _tmain(int argc, _TCHAR* argv[])
{
    av_register_all();//註冊muxers/demuxers
    avdevice_register_all();
    avcodec_register_all();//註冊codec與硬體加速器
    avformat_network_init();

    const char  *filenameSrc = "rtsp://admin:pass@192.168.10.211/axis-media/media.amp"; //Axis

    AVCodecContext  *pCodecCtx;
    AVFormatContext *pFormatCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVFrame *pFrameRGB;

    pFormatCtx = avformat_alloc_context();
    if ( pFormatCtx == NULL )
        return -8;

    //打開檔案，建立AVFormatContext以供後續decode使用
    if ( avformat_open_input( &pFormatCtx, filenameSrc, NULL, NULL ) != 0 ) {
        std::cout << "Open File Error 12" << std::endl;
        return -12;
    }

    //判斷檔案內是否有stream相關資訊
    if ( av_find_stream_info( pFormatCtx ) < 0 ) {
        std::cout << "Get Stream Information Error 13" << std::endl;
        av_close_input_file( pFormatCtx );
        pFormatCtx = NULL;
        return -13;
    }
    av_dump_format( pFormatCtx, 0, filenameSrc, 0 );
    int video_stream_index = -1;

    //顯示此媒體有幾個stream
    for ( int i = 0; i < pFormatCtx->nb_streams; i++ ) {
        //判斷此stream是否屬於video
        if ( pFormatCtx->streams[i]->codec->coder_type == AVMEDIA_TYPE_VIDEO ) {
            video_stream_index = i;
            break;
        }
    }
    //沒有找到可用的video stream
    if ( video_stream_index < 0 ) {
        std::cout << "Video stream was not found Error 14" << std::endl;
        av_close_input_file( pFormatCtx );
        pFormatCtx = NULL;
        return -14;
    }

    //根據codec id找到對應的codec
    pCodecCtx = pFormatCtx->streams[video_stream_index]->codec;
    pCodec  = avcodec_find_decoder( pCodecCtx->codec_id );
    if ( pCodec == NULL ) {
        std::cout << "codec not found Error 15" << std::endl;
        return -15;
    }

    if (avcodec_open2( pCodecCtx, pCodec, NULL ) < 0) {
        std::cout << "Open Codec Error 16" << std::endl;
        return -16;
    }

    //配置一個AVFrame，準備用來放置待會解開的影像資料
    pFrame    = avcodec_alloc_frame();
    pFrameRGB = avcodec_alloc_frame();

    AVPixelFormat pFormat = AV_PIX_FMT_RGB24 ;
    int numBytes  = avpicture_get_size( pFormat, pCodecCtx->width, pCodecCtx->height );
    uint8_t *buffer = (uint8_t *)av_malloc( numBytes * sizeof(uint8_t) );
    avpicture_fill( (AVPicture *)pFrameRGB, buffer, pFormat, pCodecCtx->width, pCodecCtx->height );

    int y_size  = pCodecCtx->width * pCodecCtx->height;
    AVPacket *packet = (AVPacket *)malloc(sizeof(AVPacket));
    av_new_packet( packet, y_size );

    int res;
    int frameFinished;
    while ( res = av_read_frame( pFormatCtx, packet ) >= 0 )
    {
        if ( packet->stream_index == video_stream_index ) {
            avcodec_decode_video2( pCodecCtx, pFrame, &frameFinished, packet );

            if (frameFinished) {
                struct SwsContext *img_convert_ctx;
                img_convert_ctx = sws_getCachedContext( NULL,
                                                        pCodecCtx->width,
                                                        pCodecCtx->height,
                                                        pCodecCtx->pix_fmt,
                                                        pCodecCtx->width,
                                                        pCodecCtx->height,
                                                        AV_PIX_FMT_BGR24,
                                                        SWS_BICUBIC,
                                                        NULL,
                                                        NULL,
                                                        NULL );
                sws_scale( img_convert_ctx,
                           ((AVPicture*)pFrame)->data,
                           ((AVPicture*)pFrame)->linesize,
                           0,
                           pCodecCtx->height,
                           ((AVPicture *)pFrameRGB)->data,
                           ((AVPicture *)pFrameRGB)->linesize );

                cv::Mat img( pFrame->height, pFrame->width, CV_8UC3, pFrameRGB->data[0] );
                cv::imshow( "Display" , img );
                cv::waitKey( 30 );

                av_free_packet( packet );
                sws_freeContext( img_convert_ctx );
            }
        }
    }

    av_free_packet( packet );
    avcodec_close( pCodecCtx );
    av_free( pFrame );
    av_free( pFrameRGB );
    avformat_close_input( &pFormatCtx );

    return ( EXIT_SUCCESS );
}

更多OpenCV文章請參考：OpenCV Tutorial (學習筆記)