Code in blue is to be added to each specific file.

camera.h

class Camera {
    ...
     
    //---[ Save/Load Kerframes ]------------------------------
    bool saveKeyframes(const char* szFileName) const;
    bool loadKeyframes(const char* szFileName);
    float keyframeTime(int keyframe) const;
};

camera.cpp

#include <windows.h>
#include <Fl/gl.h>
#include <gl/glu.h>
#include <fstream>

...
  
bool Camera::saveKeyframes(const char* szFileName) const
{
    std::ofstream ofsFile;
    ofsFile.open(szFileName, std::ios::out);
    if (!ofsFile.fail()) {
        ofsFile << mNumKeyframes << std::endl;
        ofsFile << NUM_KEY_CURVES << std::endl;
    
    if (mKeyframes[0]) 
        for (int i = 0; i < NUM_KEY_CURVES; ++i) {
            mKeyframes[i]->toStream(ofsFile);
        }
    
        return true;
    }
    
    return false;
}

bool Camera::loadKeyframes(const char* szFileName)
{
    std::ifstream ifsFile;
    
    ifsFile.open(szFileName, std::ios::in);
    if (!ifsFile.fail()) {
        int iCurveCount;
        int iNumKeyframes;

        ifsFile >> iNumKeyframes;
        if (iNumKeyframes <= 0)
            return false;
        mNumKeyframes = iNumKeyframes;

        ifsFile >> iCurveCount;
        if (iCurveCount != NUM_KEY_CURVES) {
            return false;
        }

        deleteCurves();
        createCurves(0.0f, 1.0f);

        for (int i = 0; i < iCurveCount; ++i) {
            mKeyframes[i]->fromStream(ifsFile);
        }

        return true;
    }
    return false;
}

float Camera::keyframeTime(int keyframe) const
{
    if (mKeyframes[0]) {
        Point ptCtrlPt;
        mKeyframes[0]->getControlPoint(keyframe, ptCtrlPt);
        return ptCtrlPt.x;
    }

    return 0.0f;
}

modelerui.cpp

inline void ModelerUI::cb_openAniScript_i(Fl_Menu_*, void*)
{
    char *szFileName = fl_file_chooser("Open Animation Script", "*.ani", NULL);
    if (szFileName) {
        if (m_pwndGraphWidget->loadScript(szFileName)) {
            endTime(m_pwndGraphWidget->endTime());
            activeCurvesChanged();
            // load the camera keyframes
            string strCamKeyframeFileName = szFileName;
            strCamKeyframeFileName += ".cam";
            m_pwndModelerView->m_curve_camera->loadKeyframes(strCamKeyframeFileName.c_str());
            // synchronize the indicator window with the loaded keyframes
            m_pwndIndicatorWnd->clearIndicators();
            for (int ikf = 0; ikf < m_pwndModelerView->m_curve_camera->numKeyframes(); ++ikf)
                m_pwndIndicatorWnd->addIndicator(m_pwndModelerView->m_curve_camera->keyframeTime(ikf));
            }
            else {
                fl_alert("Sorry! I can't load the animation script!");
        }
    }
}

...

inline void ModelerUI::cb_saveAniScript_i(Fl_Menu_*, void*)
{
    char *szFileName = fl_file_chooser("Save Animation Script As", "*.ani", NULL);
    if (szFileName) {
        string strFileName = szFileName;

        // Append the default extension
        char szExt[_MAX_EXT];
        _splitpath(strFileName.c_str(), NULL, NULL, NULL, szExt);
        if (strlen(szExt) == 0)
            strFileName += ".ani";

        if (m_pwndGraphWidget->saveScript(strFileName.c_str())) {
            // save the camera keyframes
            string strCamKeyframeFileName = strFileName + ".cam";
            m_pwndModelerView->m_curve_camera->saveKeyframes(strCamKeyframeFileName.c_str());
        }
        else {
            fl_alert("Sorry! I can't save the animation script!");
        }
    }
}