Ignore the audio side of the equation for this question.
Given: you can convert a 25 fps xvid to 23.976 fps xvid without reencoding simply by loading xvid in Vdub, use "direct copy" and change the framerate.
Question: I was wondering if you're trying to convert a Pal dvd (25 fps progressive) to Ntsc xvid, would it be less "damaging" to the video to only resize it when encoding to xvid (leave it at 25 fps). Then change the fps in Vdub as described? Or is it all the same?
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There's generally no need to change PAL sources to 23.976 fps when making Xvid AVI. Virtually everything that plays Xvid AVI can handle 25 fps just as well as 23.976 fps. I don't even change the frame size, just use PAR flags.
The video specs and goals I mentioned are necessary. I'm only asking if between the two methods to change fps - during encoding, or later with Vdub - is one more damaging than the other.
I'm tempted to say the Vdub method is less damaging, since the framerate change isnt changing the frames, but I guess flagging the player to output differently?
Assuming you're changing the framerate by slowing it down to film speed (as opposed to removing a frame every second), there may be an imperceptibly lower quality by doing it during the encoding if encoding for a specific size (as opposed to doing it using a constant quant). The reason is that by slowing it you're lengthening it a little bit and thus it'll get slightly fewer bits per frame (~4% fewer) if the bitrate for both ways is the same.
But I always do it during the encoding myself (making DVD to DVD though).
thanks, manono. Yes, slowing down with "Assumefps(23.76,true)." I plan on making a dvd conversion for myself, and an xvid for sharing; in both cases I would need to resize (especially the xvid to make the overall file size smaller). I'll be slowing down the audio with it.