ffmpeg问题汇总及解决方案

1：
如果数据是rtp/rtsp传输的话，ffmpeg会每隔30s（哪里设置该值？）发送一个keepalive包，如果ipc支持GET_PARAMETER命令，就发该命令等ipc回复以确认ipc还活着。
某些ipc(IPCamera)不支持GET_PARAMETER的rtsp命令。则会通过OPTIONS *来是keepalive，不过这会导致连接断掉
原代码，及修改部分如下。先这样处理，有时间再研究原代码为什么不这么处理。

//ffmpeg/libavformat/rtspdec.c rtsp_read_packet()
if (!(rt->rtsp_flags & RTSP_FLAG_LISTEN)) {
        /* send dummy request to keep TCP connection alive */
        if ((av_gettime() - rt->last_cmd_time) / 1000000 >= rt->timeout / 2 ||
            rt->auth_state.stale) {
            if (rt->server_type == RTSP_SERVER_WMS ||
                (rt->server_type != RTSP_SERVER_REAL &&
                 rt->get_parameter_supported)) {
                ff_rtsp_send_cmd_async(s, "GET_PARAMETER", rt->control_uri, NULL);
            } else {
                // ff_rtsp_send_cmd_async(s, "OPTIONS", "*", NULL);                 //原代码
                ff_rtsp_send_cmd_async(s, "OPTIONS", rt->control_uri, NULL);        //修改后的代码，这样就算ipc不支持GET_PARAMETER的命令可以keepalive了
            }
            /* The stale flag should be reset when creating the auth response in
             * ff_rtsp_send_cmd_async, but reset it here just in case we never
             * called the auth code (if we didn't have any credentials set). */
            rt->auth_state.stale = 0;
        }
    }

2：
如果数据是rtp/rtsp/tcp传输，如果没有设置stimeout（socket timeout），那么server断线后av_read_frame会阻塞

AVFormatContext *pFormatCtx = NULL;
    AVPacket        packet;
    AVDictionary *optionsDict = NULL;
    char *streamurl1 = "rtsp://test:test@192.168.11.111:554/test.stream";

    // Register all formats and codecs
    av_register_all();
    avformat_network_init();

    pFormatCtx = avformat_alloc_context();
    av_dict_set(&optionsDict, "rtsp_transport", "tcp", 0);                //采用tcp传输
    av_dict_set(&optionsDict, "stimeout", "2000000", 0);                  //如果没有设置stimeout，那么把ipc网线拔掉，av_read_frame会阻塞（时间单位是微妙）

    // Open video file
    if(avformat_open_input(&pFormatCtx, streamurl, NULL, &optionsDict)!=0){
        printf("linesize = %d\n", __LINE__);
        return -1; // Couldn't open file
    }

    // Retrieve stream information
    if(avformat_find_stream_info(pFormatCtx, NULL)<0){
        printf("linesize = %d\n", __LINE__);
        return -1; // Couldn't find stream information
    }

    // Find the first video stream
    int videoStream=-1;
    for(i=0; i<pFormatCtx->nb_streams; i++){
        if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
            videoStream=i;
            break;
        }
    }

    if(videoStream==-1){
        printf("linesize = %d\n", __LINE__);
        return -1; // Didn't find a video stream
    }

    // Read frames and save first five frames to disk
    while(av_read_frame(pFormatCtx, &packet)>=0) {
        av_free_packet(&packet);
    }

如果是ffmpeg2.0.1版本的话，添加一句就ok了。可是旧版本ffmpeg1.2.*没有stimeout这个字段可以设置
那么只好自己添加了。
在ffmpeg/libavformat/rtsp.h  struct RTSPState添加一个stimeout字段

typedef struct RTSPState {
    /**
     * timeout of socket i/o operations.(this version do not have this segment. added by yqing, refer to ffmpeg-2.0.1)
     */
    int stimeout;
} RTSPState;

在ffmpeg/libavformat/rtsp.c  ff_rtsp_options添加一个stimeout字段

const AVOption ff_rtsp_options[] = {
    { "stimeout", "timeout (in micro seconds) of socket i/o operations.", OFFSET(stimeout), AV_OPT_TYPE_INT, {.i64 = 0}, INT_MIN, INT_MAX, DEC },    //添加这行代码
    RTSP_REORDERING_OPTS(),
    { NULL },
};

在ffmpeg/libavformat/rtsp.c  ff_rtsp_connect函数修改部分代码如下

//ff_url_join(tcpname, sizeof(tcpname), "tcp", NULL, host, port, NULL);                            //原代码
  ff_url_join(tcpname, sizeof(tcpname), "tcp", NULL, host, port, "?timeout=%d", rt->stimeout);     //修改后的代码