29.97 -> 23.976 FPS Adjustment of sound needed?

[StainlessSteel]

Hello again.

Another fine-tune question. It deals with audio content this time. AFAK the audio stream of a movie doesn't play independently aside the video stream, but linked to each video frame. Therefore, it's necessary to pitch the audio data, when an NTSC DVD movie gets adjusted from 29.97 to 23.976 FPS.

Generally I use GordianKnot 0.30 alpha for the whole conversion process and already saw BeSweet arguments for correcting the audio speed to get synced to readjusted movie FPS.

My question is this: If I want to include AC3 in my encoded movie, do I have to pitch the AC3 audio stream manually? Does DGIndex (DVD2AVI) pitch automatically when using Force Film? Do I have to prepare the sound manually when I use IVTC?

Thanks,

Stainless

[KpeX]

Hi,

When doing an IVTC operation, audio adjustment is normally not needed, because (in theory) only duplicate frames are removed, and the change in the number of frames is balanced by a change in framerate.

The only time an audio stretch operation is necessary is when the number of frames is changed without changing the framerate, or vice versa.

To really understand the subject, I'd recommend taking a look at the excellent tutorial put together by a few of the mods: http://www.doom9.org/ivtc-tut.htm

[StainlessSteel]

Thanks a lot. I've read the tutorial you mentioned, but it doesn't really explain the relation between audio streams and video streams and how they work together.

So what about movies I apply FORCE FILM at? Does DVD2AVI (DGIndex) does necessary audio stretch operations?

[manono]

Hi-

No stretch is needed whether you apply Force Film, or you perform IVTC. In both cases the video length stays exactly the same. As KpeX said, the fewer frames are balanced by the lower framerate.