如何用.sdp打开本地live555文件

Question

我需要打印每帧时间(UTC)通过获得每个RTP时间戳，但vlc API不支持这个特性。因此，我刚听说VLC库调用live555库来解析RTSP，并在testRTSPClient(官方网站testRTSPClient)中找到函数afterGettingFrame，打印出每个帧的UTC时间。

我只是去使用testRTSPClient在本地PC中打开.sdp文件。但不起作用。它只能打开"rtsp://123.434.12.4/3523swdawd.sdp“这个表单，以此类推。

我需要安装rtsp服务器吗？因为我发现它需要向服务器发送一些特殊的命令(安装、播放、选项)。

如果testRTSPClient只能处理rtsp://123.434.12.4/3523swdawd.sdp这种形式的url，那么testRTSPClient媒体播放器如何处理本地.sdp文件而不设置RTSP服务器？

提示:这个本地.sdp文件是给我的本地IP相机的。我可以用VLC播放器从IP摄像头播放视频帧，但我只想使用testRTSPClient处理本地.sdp文件并打印视频帧的UTC时间，有谁能解决这个问题呢？

Answer 1

为了接收使用live555的SDP文件描述的RTP流，您需要：

1. 从SDP创建一个MediaSession (这将创建关联的MediaSubsession )
2. 启动MediaSubsession以便打开接收RTP/RTCP的UDP端口
3. 创建一个重载的MediaSink来接收RTP帧
4. 启动这个水槽

受testRTSPClient.cpp启发的天真实现可能如下所示：

#include "liveMedia.hh"
#include "BasicUsageEnvironment.hh"

UsageEnvironment& operator<<(UsageEnvironment& env, const MediaSubsession& subsession) 
{
    return env << subsession.mediumName() << "/" << subsession.codecName();
}

#define DUMMY_SINK_RECEIVE_BUFFER_SIZE 100000

class DummySink: public MediaSink 
{
    public:
        static DummySink* createNew(UsageEnvironment& env,
                      MediaSubsession& subsession, // identifies the kind of data that's being received
                      char const* streamId = NULL) // identifies the stream itself (optional)
        {
              return new DummySink(env, subsession, streamId);
        }

    private:
        DummySink(UsageEnvironment& env, MediaSubsession& subsession, char const* streamId)  
            : MediaSink(env), fSubsession(subsession) 
        {
            fStreamId = strDup(streamId);
            fReceiveBuffer = new u_int8_t[DUMMY_SINK_RECEIVE_BUFFER_SIZE];
        }

        virtual ~DummySink()
        {
            delete[] fReceiveBuffer;
            delete[] fStreamId;
        }

        static void afterGettingFrame(void* clientData, unsigned frameSize,
                    unsigned numTruncatedBytes,
                    struct timeval presentationTime,
                    unsigned durationInMicroseconds)
        {
            DummySink* sink = (DummySink*)clientData;
            sink->afterGettingFrame(frameSize, numTruncatedBytes, presentationTime, durationInMicroseconds);        
        }
        void afterGettingFrame(unsigned frameSize, unsigned numTruncatedBytes,
                 struct timeval presentationTime, unsigned durationInMicroseconds)
        {
            if (fStreamId != NULL) envir() << "Stream \"" << fStreamId << "\"; ";
            envir() << fSubsession.mediumName() << "/" << fSubsession.codecName() << ":\tReceived " << frameSize << " bytes";
            if (numTruncatedBytes > 0) envir() << " (with " << numTruncatedBytes << " bytes truncated)";
            char uSecsStr[6+1]; // used to output the 'microseconds' part of the presentation time
            sprintf(uSecsStr, "%06u", (unsigned)presentationTime.tv_usec);
            envir() << ".\tPresentation time: " << (int)presentationTime.tv_sec << "." << uSecsStr;
            if (fSubsession.rtpSource() != NULL && !fSubsession.rtpSource()->hasBeenSynchronizedUsingRTCP()) 
            {
                envir() << "!"; // mark the debugging output to indicate that this presentation time is not RTCP-synchronized
            }
            envir() << "\tNPT: " << fSubsession.getNormalPlayTime(presentationTime);
            envir() << "\n";

            // Then continue, to request the next frame of data:
            continuePlaying();          
        }

    private:
        virtual Boolean continuePlaying()
        {
            if (fSource == NULL) return False; // sanity check (should not happen)          
            fSource->getNextFrame(fReceiveBuffer, DUMMY_SINK_RECEIVE_BUFFER_SIZE, afterGettingFrame, this, onSourceClosure, this);
            return True;
        }

    private:
        u_int8_t* fReceiveBuffer;
        MediaSubsession& fSubsession;
        char* fStreamId;
};

int main(int argc, char** argv) 
{
    TaskScheduler* scheduler = BasicTaskScheduler::createNew();
    UsageEnvironment* env = BasicUsageEnvironment::createNew(*scheduler);

    if (argc < 2) 
    {
        *env << "Usage: " << argv[0] << " file.sdp\n";
        return 1;
    }
    const char* filename = argv[1];
    FILE* file = fopen(filename,"r");
    if (file == NULL)
    {
        *env << "Cannot open SDP file:" << filename << "\n";        
        return 1;
    }
    fseek(file, 0, SEEK_END);
    long size = ftell(file);
    fseek(file, 0, SEEK_SET);
    char sdp[size];
    fread(sdp,size,1,file);
    fclose(file);

    MediaSession* session = MediaSession::createNew(*env, sdp);               
    if (session == NULL)
    {
        *env << "Failed to create a MediaSession object from the SDP description: " << env->getResultMsg() << "\n";     
        return 1;
    }

    MediaSubsessionIterator iter(*session);
    MediaSubsession* subsession = NULL;
    while ((subsession = iter.next()) != NULL) 
    {
        if (!subsession->initiate (0))
        {
            *env << "Failed to initiate the \"" << *subsession << "\" subsession: " << env->getResultMsg() << "\n";
        }
        else
        {
            subsession->sink = DummySink::createNew(*env, *subsession, filename);
            if (subsession->sink == NULL)
            {
                *env << "Failed to create a data sink for the \"" << *subsession << "\" subsession: " << env->getResultMsg() << "\n";           
            }
            else
            {
                subsession->sink->startPlaying(*subsession->rtpSource(), NULL, NULL);
            }
        }
    }

    char eventLoopWatchVariable = 0;
    env->taskScheduler().doEventLoop(&eventLoopWatchVariable);

    return 0;
}

运行程序时，给出包含SDP的文件的路径作为参数，将读取RTP流、打印帧大小和每个帧的时间戳。

类似于：

Stream "ffmpeg.sdp"; video/H265:    Received 5131 bytes.    Presentation time: 1442350569.228804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 7917 bytes.    Presentation time: 1442350569.268804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 2383 bytes.    Presentation time: 1442350569.308804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 7780 bytes.    Presentation time: 1442350569.348804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 1773 bytes.    Presentation time: 1442350569.388804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 9580 bytes.    Presentation time: 1442350569.428804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 7934 bytes.    Presentation time: 1442350569.468804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 2180 bytes.    Presentation time: 1442350569.508804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 10804 bytes.   Presentation time: 1442350569.548804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 7801 bytes.    Presentation time: 1442350569.588804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 7816 bytes.    Presentation time: 1442350569.628804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 4028 bytes.    Presentation time: 1442350569.668804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 7959 bytes.    Presentation time: 1442350569.708804!   NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 8062 bytes.    Presentation time: 1442350569.794000    NPT: 0.000000
Stream "ffmpeg.sdp"; video/H265:    Received 8014 bytes.    Presentation time: 1442350569.834000    NPT: 0.000000