Opening mp4 videos with different Frame Rate for Quality Comparison

[avzabr]

Hello,
Sorry if i have raised the topic which already exists..I have checked the forum - but have not found the answer.

The question is the following:
I have the MSU VQMT tool which compares the quality of the original and the optimized videos by checking the same frames of each video. And i am faced with the problem of comparison mp4 videos with Variable Frame Rate and Constant Frame Rate. I use the Avisynth script to open mp4 and i can see that program compares the wrong frames: frame of original videos with frame of optimized video, but several seconds later or prior. Therefore i get the wrong results of tool.

So the question is:
How to open the Original and Optimized variants of MP4 videos with Avisynth script to compare exactly the right frames?
The following cases could be:
1) The VFR mp4 is optimized to the VFR mp4
2) The CFR mp4 is optimized to the CFR mp4
3) The VFR mp4 is optimized to the CFR mp4

I assume that for the 1st case files should be opened in the following way:
clip = DirectShowSource("D:\Qualitytest\Test\orig\00001-LUjn3RpkcKY.mp4", converfps=true)
return clip
But original and optimized frames are very shifted.

For the second case:
clip = DirectShowSource("D:\Qualitytest\Test\orig\video.mp4")
framePerSecond=clip.FrameRate
clip1 = DirectShowSource("D:\Qualitytest\Test\optimized\video.mp4",fps = framePerSecond)
return clip1
The original and optimized frames are almost the same, but not exacly

For the 3rd case i even do not know what to do..

PS: I do not know in which way videos have been optimized. But need to compare the right frames and get the results..

Does anybody have any suggestions?