我通过live555打开本地的SDP文件，然后通过这个文件为我的IP Camera建立个传输会话，已经成功，DummySink中的 afterGettingFrame这回调函数能不间断的调用，我直接把表示每帧fReceiveBuffer和frameSize传入了FFMPEG的解码器，但是 avcodec_decode_video2总是调用失败。我查看了一些帧的fReceiveBuffer，里面没有插入相关的SPS和PPS，没有0x00000001的标记，因为解码器要解码IDR帧必须通过SPS和PPS正确初始化，才能够解码，我的SDP文件里面有PPS和SPS的Base64编码，我需要怎么处理这个SPS和PPS才能正确初始化解码器？不然解码器是无法解码H264的。FFMPEG中的AVCodecContext中的extradata也没有相关文档描述怎么用，听说是用来存放SPS和PPS的，如果是，该怎么用？我需要把SPS和PPS的Base64的编码解出来再传入吗？还是直接就传入（插入）SPS和PPS的Base64版本？

以下是我的代码片断：

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_s(uSecsStr, 7, "%06u", (unsigned)presentationTime.tv_usec);
        envir() << ".\tPresentation time: " << (int)presentationTime.tv_sec << "." << uSecsStr;


        gffmpeg->decodeFrame(fReceiveBuffer, frameSize, presentationTime.tv_sec, presentationTime.tv_usec);


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

void  QFFmpeg::decodeFrame(uint8_t* frameBuffer, int frameLength, long second, long microSecond)
{
    if (frameLength <= 0) return;

    int frameFinished = 0;

    AVPacket framePacket;
    av_init_packet(&framePacket);

    framePacket.size = frameLength;
    framePacket.data = frameBuffer;

    int ret = avcodec_decode_video2(m_pAVCodecContext, m_pAVFrame, &frameFinished, &framePacket);

    if (ret < 0)
    {
        qDebug() << "Decode error";
        return;
    }

    if (frameFinished)
    {
        m_playMutex.lock();

        m_videoWidth = m_pAVFrame->width;
        m_videoHeight = m_pAVFrame->height;

        m_pSwsContext = sws_getContext(m_videoWidth, m_videoHeight, AVPixelFormat::AV_PIX_FMT_YUV420P, m_videoWidth, m_videoHeight, AVPixelFormat::AV_PIX_FMT_RGB24, SWS_BICUBIC, 0, 0, 0);


        sws_scale(m_pSwsContext, (const uint8_t* const *)m_pAVFrame->data, m_pAVFrame->linesize, 0, m_videoHeight, m_pAVPicture.data, m_pAVPicture.linesize);


        char timestamp[100];

        sprintf_s(timestamp, 100, "Time Stamp is: %ld.%ld", second, microSecond);


        //发送获取一帧图像信号
        QImage image(m_pAVPicture.data[0], m_videoWidth, m_videoHeight, QImage::Format_RGB888);

        QPainter pen(&image);
        pen.setPen(Qt::white);
        pen.setFont(QFont("Times", 10, QFont::Bold));
        pen.drawText(image.rect(), Qt::AlignBottom, QString(timestamp));
        emit GetImage(image);
        m_playMutex.unlock();
    }
}

以下是解码器的初始化，都能正确返回

bool QFFmpeg::Init()
{
    


    m_pAVCodec = avcodec_find_decoder(AV_CODEC_ID_H264);

    if (!m_pAVCodec)  return false;


    m_pAVCodecContext = avcodec_alloc_context3(m_pAVCodec);
    


    if (avcodec_open2(m_pAVCodecContext, m_pAVCodec, NULL) < 0)  return false;
    
    
    return true;
}