Video is being opened by Avisynth's DirectShowSource, need to change that

[Compositor]

I use Aegisub's video player to get the exact frame number of a video to make cuts. On this particular video, I get the following warning:

The file is being opened using Avisynth's DirectShowSource, which has unreliable seeking. Frame numbers might not match the real number. PROCEED AT YOUR OWN RISK!

True enough, on Aegisub's audio display, where it usually shows the location of keyframes, there are no keyframes indicated.

I try opening other video files in Aegisub and there are no issues. This is a quirk of this particular video file. I try to see if the issue will go away if the video is reencoded, I get the same thing on the encoded result.

So, what kind of property on a video would prompt the use of Avisynth's DirectShowSource to display it and how can I change that? I can reencode the video if I have to. I plan to cut out a piece of this video and join it to another video, both will be encoded to the same settings and I don't want this issue causing problems in the joined video as well.

I would be most grateful for any help.

Edit: Tried just cutting the video and the quirk went away and I can get accurate frame numbers now. I still would be interested in a solution that did not involve cutting. Next time, I may not have the margin to cut anything.

[sekininsha]

I use Aegisub's video player to get the exact frame number of a video to make cuts. On this particular video, ......

for the same I use VirtualDub2 directly ...

https://www.videohelp.com/software/VirtualDub2

[Compositor]

for the same I use VirtualDub2 directly ...

Is it drag-and-drop video and start playing it now? I remember VirtualDub1 a long time ago, I had no idea how to set it up to display a video to manipulate. Never used it again.
I use Aegisub for editing subtitles, so this is a handy secondary use.