Audio Desynch with DivX 5.02

[DJ Alik]

This is what I did to encode "The Patriot". Since it only has 5.1 AC3 stream i converted it into 2.0 stream with the following:

I concerted 5.1 448kbps AC3 stream into WAV using AZID 1.8
Normalized it using Sound Forge 6.0
Reencoded it back into AC3 2.0 160kbps using Soft Encode and muxed it with the movie folling the Gordian Knot guide. I used b-frames and GMC no psych no qpel.

Now at the beginning the movie seems fine but towards the middle you get desynching and at the end it gets really bad.

I thought the problem was the transcoding part but then I did "The Gladiator" and just Muxed the supplied 192kbps Audio stream into the encoded video. I also get the desynching. Can anyone help?!?

[DJ Bobo]

Why using AC3 if you can use MP3 and get 100% synch sound??!! :confused:

1) MP3 has slightly better sound quality
2) MP3 encoding is faster
3) MP3 has universal compatibilty
4) MP3 decoding is faster

[mustaneekeri]

Ya, it's absolytely no sense use AC3 exept for more than 2 channels audio.

[DJ Alik]

I have always used AC3 with my divx movies and never had desynch problems. The reason i use AC3 so that I can keep the sorround sound. I am not sure if the MP3 format keeps the Dolby Sorround in it's encoding.

[Acaila]

You're downmixing the AC3 when you re-encode it into less channels then the original. You'll also downmix when you encode the 6ch AC3 straight into a 2ch MP3.

In both ways you'll keep the illusion of surround sound. So there's really no sense in using 2ch AC3 when you can also use 2ch MP3 for the reasons bobotns mentioned.

However I personally prefer Vorbis over MP3. Better quality at low bitrates. And a whole bunch of other things which I won't mention here. Check the New A/V section for more info on Vorbis.

[DJ Bobo]

@ DJ Alik
As Acaila said, AC3 2.0 is no better than MP3 in keeping Surround informations.
Just to keep 100% sure your MP3 has 100% Dolby Surround code: encode it in Stereo mode, not in Joint Stereo.

--off topic--
@ Acaila
Your system is very nice, but your VGA card doesn't suit your profile, you better got an ATi Radeon 8500 to enjoy best video acceleration and features on the market ;)

[DJ Alik]

But how would you explain desynched sound when I just use the ac3 that comes on the VOB without any modifications like in Gladiator (it includes 192kbps 2.0 ac3 stream) If i just mux it in i should have the perfect mix but i get the desynched sound with this new DivX 5.02 Never had a problem with 4.12 or 5.01

[DJ Alik]

Just for a test i muxed the video with the supplied 5.1 AC3 . Same story, in the beginning of the movie the synching is fine but it gets progressively worse towards the end.

[Acaila]

If you still get sync issues with the 5.1 AC3 stream you're probably doing something wrong during interleaving.

GKnot isn't supposed to give you async, even with AC3, but you'd best do it manually in Nandub with these settings:
384kbps AC3 (5.1) -> 160 ms preload, 160 ms interleaving
192kbps AC3 (2.0) -> 96 or 64 ms preload, 96 or 64 ms interleaving.
Those values should work for most people.

Ps.
Are you sure your system is fast enough to keep up? Turning off DivX5's post-processing solves many sync problems.

@bobotns:
I agree, my video card seems a little off compared to the rest. But I've had it for quite a while (and I paid a fair amount of money for it when it just came out, ok that was stupid I know :)), and it's never given me any problems. Besides, decoding is already fast enough, and a faster video card isn't going to speed up encoding anyway (although TV-out would have been nice...).

[DJ Alik]

Even if I turn all the post processing to minimum it gives me desynched audio. And my system should be fast enough:

AMD Tbird 1.4Ghz CPU, PC2100 256 Mb ram, GeForce 3 TI500 video, SB Audigy sound card, WD 7200rpm 40Gb Hard Drive.

See I have been doing this for quite awhile now, and I never had problems with desynched sound, only with 5.02. When I open my old movies that were done with previous versions of the codec, everything is perfect

[jggimi]

Stupid question, but have you tried syncing with the wav file you got from azid? Yeah, it takes up a lot of space, but that could tell you if your conversion from wav -> ac3 was at fault. (You could also convert from wav -> mp3 and try the same thing.)

[DJ Bobo]

@ jggimi
He tried with the original AC3 also, doesn't work

@ DJ Alik
Which program had you used to extract the AC3? you should *ALWAYS* do it in DVD2AVI while saving the project. You get a delay, that you have to enter while muxing and for interleaving: I always got synch sound with 96ms/96ms and I have only a PIII @667MHz.

[DJ Alik]

I used DVD2AVI 1.76 to extract the AC3.

When muxing I used nandub and I prereload 500ms and interlieve after each frame

[DJ Bobo]

preload: 96ms
interleaving: 96ms

and enter delay of course, as is (negative if it is negative, positive if it positive)