I am using Aegisub to fix the timing of subtitle files of movies. There is a wavelength diagram and I can set the start\end time of a line by clicking on that diagram. I am finding the point in which a person stops talking and then I set the end time. If I load the movie in Aegisub then I can check if the end time is ok.

I can press W after I set the end time of a line to listen to 500ms after the end time of a line. If I hear the end part of a word when I press W then that means the end time of that line is too early. For example, assume that the last word in the line is "hello" and I hear part of the o in hello when I press W. The o is the end part of the word. I am setting the end time of a line correctly and I am not hearing the end part of a word when I press W.

The problem is that if I play the movie in a media player outside Aegisub then I am sensing that the subtitle line is going away a bit early and then person says the end part of the word. I am unsure if the end part of the word is said exactly when the subtitle line goes away or just after the subtitle line goes away. That same line is perfect when I play it in the media player of Aegisub and I am not hearing the end part of a word when I press W.

I want to ask why is this happening? Is the fps of the movie when it plays in the media player of Aegisub different from the fps of the same movie when it plays in a media player outside Aegisub? I don't think it's the same. For example assume that I create a subtitle line for text which shows in the movie and I time the subtitle line so it shows exactly when the text shows in the movie and it goes away exactly when the text goes away in the movie and it's perfect when it plays in the media player of Aegisub. However, if I play that same part in a media player outside Aegisub then the timing of the subtitle line doesn't match the text in the movie.

If what I said is correct then how do I make the fps of the movie when it plays in the media player of Aegisub the same as the fps of the movie when it plays in a media player outside Aegisub like for example MPC-HC and SM Player?