Different Output FPS Alters Video Length?

[CybermatriX]

Can a different encoded FPS increase the video length?

For example, if my source video files are 30 FPS and the final encoded file is 24 FPS, can a lower final encoded FPS make the actual video length different than that of the 30 FPS, if watching the 30 FPS files one right after another?

[manono]

It can change the length, but it doesn't have to. A 24fps video that has had one frame out of every 5 removed from the 30fps source, perhaps as part of an IVTC process (probably the case in your example), will have the same length as the 30fps video. If you simply slow a 30fps video to 24fps, then of course the 2 lengths will differ.