exporting a looped movie

Tried exporting a bidirectional movie (plays forward and then plays in reverse). It's smoother than just letting the video jump back to the beginning but there's still a visible transition when the rings change direction.

int PassFrames = m_RangeLast - m_RangeFirst + 1;
int TotalFrames = (PassFrames - 1) * 2;
pd.Create();
int j = m_RangeLast;
pd.SetRange(0, TotalFrames);
for (int i = 0; i < TotalFrames; i++) {
    if (i >= PassFrames)
        sm.Seek(--j);
    sm.Read();
    HBITMAP bm = View->MakeDIB(&OutFrameSize, &m_InFrameSize, GetScaleToFit());
    bool    retc = bta.AddFrame(bm);
    DeleteObject(bm);
    if (!m_DisplayOutput)   // prevent view from painting
        View->ValidateRect(NULL);   // must revalidate before SetPos
    pd.SetPos(i);
    if (pd.Canceled())
        return(IDCANCEL);
}