AC3 Delays, why?

[Bulletproof]

Hey guys, i've noticed in the recent guides that you should correct delays that DVD2AVI reports (negative or positive) on your audio files. But, when I used to just used azid then go to mp3 I noticed no problems with any of the encodings, none of them were off sync or anything. And even in doom9's older guides, it has no mention of messing with delays at all, so how come we have to now? and also why are there delays in the AC3's anyway? Thanks in advance.

[Acaila]

If the delay is under 100ms odds are you won't even hear the difference. But just to make it completely correct we use them.

[Doom9]

most movies I dealt with actually had no delay. and when using a ds filter and playing the vobs I think the delay is corrected already so such a correction is not necessary for vob2audio/graphedit. And in the case of the azid guides I recall not having any movies with a delay so I never bothered with it.. but recently I had more and more movies that had a delay so I put it into the guides.

[kallekill]

So if you are using vob2audio or graphedit and use the delay-value when muxing you put it out of sync?

[Doom9]

I would assume so. But as I said.. most of the movies I encoded so far had 0 delay. But since you play vobs in ge, you will start at the point 0:00:00.000 in the video, so the delay will already have been compensated. This may also be the reason why initially azid wasn't so popular, people were getting out of synch problems because they did not adjust the delay (no guide ever spoke about it), so everybody kept using ge/v2a where there are no such problems

[Zhnujm]

most delay i ever had was 22840ms !!! (shang high noon pal).
and this setting was correct (the first 20s was only a black picture without sound)

[Atlantis]

I’m also wondering about this. In the guide it says that you should enter the audio delay including the sign. Shouldn’t it be the opposite? You should change the sign! If the audio delay is –290 ms, you should enter +290 ms to have audio sync! What am I missing?

[Ned]

Just look in the .txt file that Smartripper creates and it will show the delay values for the various streams.

Use exactly what it says.

(-167ms) you put -167 when interleaving.

To those above who can't see the desync with 100ms or less, are you blind? even 50ms is easily detectable.

[Doom9]

@ned: I think less sensitive people are lucky.. they can use mpeg2avi (the worst ever asynch encoder) for NTSC titles ;)

and do you honestly think I can't detect delays of 200ms? (100ms delay, plus switching the sign makes 200ms).. I sure can so the guides are definitely correct.

[Atlantis]

So when the smartripper, dvd2avi and vstrip say that an AC3 has a delay of –190ms, they actually mean that the audio track has a delay of +190ms to the video? Right?

[Zhnujm]

a delay of -190ms means the audio starts 190ms BEFORE the video. thats why you enter -190 in the audio delay box.

[Atlantis]

a delay of -190ms means the audio starts 190ms BEFORE the video. thats why you enter -190 in the audio delay box.
I’m sorry but you do the math. If a delay of -190ms means the audio starts 190ms BEFORE the video, when you enter -190 in the audio delay, you make it –380 ms!.

I have to clarify, I know that an audio delay of –190ms means that the audio starts 190ms sooner. All I’m saying is that when smartripper and … report an audio delay of –190ms and you have to enter -190, then they only mean you should enter –190 but the audio delay in the ac3 file should actually be +190ms, that’s all!

[Doom9]

you're misunderstanding something. As you correctly stated, a delay of -190ms means the audio starts 190ms sooner than the video. But, entering -190ms as offset cuts off the first 190ms from the audio track, so then once the video starts the audio is at 190ms already, which is exactly what we want. Alternatively you could delay the video by 190ms by inserting black frames but that's more problematic...

[Atlantis]

Ah, yes now I get it! Thanks Doom9, your explanation made it clear to me. That’s why I insisted because it wasn’t clear to me. It’s always good to also understand new things, you will never forget them later! Thanks to everyone!

PS - It’s also like if the original audio and video were in perfect sync and you perform a +190ms delay, you achieve the file that says it has a –190ms delay! ;) :D