mpeg audio / video gradually goes out of synch

[CaptainChaos]

Hi

I have a concert video (vcd quality at best), and while the sound>video start off in synch, it seems they gradually get further apart, with the audio ending up approx. 3 seconds ahead of the video at the end of 1hr 15 minutes.

Is there any way of stretching/shrinking either to make it more in time with each other?

[mats.hogberg]

In what format is your video? (codec) and what do you intent to play it on?

/Mats

[CaptainChaos]

Ok .... I just GSpotted it & it came up with this .....

Stream Type & A/V Interleave = Type: AVI, IMRR: 1.00, I/L: 24 vid frames (1000 ms) Split: Yes.

Codec = 4CC: DIV3/div4, Name: DivX 3 Fast-Motion

Runtime: 01:13:24 (105,700 fr)

x:y = 320x240 (1.33:1) [=4:3]

Audio Codec = 0x0055(MP3) ID'd as MPEG-1 Layer 3

Bitrate: 96 kb/s (48/ch, stereo) CBR

Fs = 44100 Hz

Video Src Type = 4cc: DIV3

Audio Src = MPEGLAYER3 (MP3) (0x0055)

Video Path = (S) --> AVI Splitter --> DivXAntiFreeze --> DivX Decoder Filter --> (R)

Audio Path = (S) --> AVI Splitter --> MPEG Layer-3 Decoder --> (R)


I hope that makes more sense to you than it does to me!

I burnt it to vcd format & it goes out of synch on both pcs (before tmpgenc) & standalone dvd player (on cdr after tmpgenc).

[mats.hogberg]

Ah, it isn't out of sync to begin with, but goes out of sync after converting to VCD mpg!
It sems to be 24 FPS, that's the problem. What's your target frame rate? I bet it's 23.976.
The problem is that the video gets a little slowed down, but the audio plays at the same speed as before.
Extract the audio, decode to WAV, make it 0.999 times original length with GoldWave time warp function, then use this new wav as audio source when encoding.

/Mats

[CaptainChaos]

Thank you very much for suggesting GoldWave .... I have d'loaded the Trial version ..... 3000 button presses to go! lol

Ok .... Tell me if what I have done is right or not

I opened the "original" file, which gave me a time length of 1.13.25.133

I found a button in GoldWave called "Time Warp", went to "length" and did one .wav reduced by 2 seconds (time = 1.13.23.000) and one reduced by 3 seconds (time = 1.13.22.000).

So now - I use TMPGenc to encode each new one, but instead of using the original avi as the audio, I use one of the new ones I saved (as a .wav) & try that till I get it right?

It's quite difficult to work out the exact time it goes out of synch by, but I guess I can mess about with the "time warp" till it gets it pretty much spot on, yes?

Thanks again!

[mats.hogberg]

Yes, that seems about right. Old AVI as video source, new wav as audio source, TMPGEnc settings the same as before on all other points.
I don't think you'll notice a point where it suddenly is out of sync - (if the AVI is OK without bad frames and stuff) - Here we're talking about audio "drift" where it gets 1/1000 sec more out of sync for each second. Unnoticable at first, but unwatch/listenable after an hour...
But hey wait - you say the audio is ahead of the video - then you should make the audio longer (in time) to compensate - not shorter!?!

/Mats

[CaptainChaos]

YOIKES!!!

You're right ..... there was me being all smug & self-congratulatory & you made the very good point that yes, the audio is ahead of the video by 3(ish) seconds by the end ..... hmmmm ..... ok ..... will try extending it a bit .... will let you know how it goes & thank you very much for your help!

[CaptainChaos]

oh hang on a minute!!!!

The audio is ahead of the video, therefore surely the audio needs to be shrunk in size to fit the video??

The audio ends 3 seconds or so before the video, therefore, surely I need to shrink the audio, not extend it?

Brain Fade will occur in 5 ... 4 ... 3 ... 2 ...

[mats.hogberg]

Yes, if the audio ends before video, it has to be made longer, right?
If one piece of string ends before the other, it has to be made longer, or s-t-r-e-c-h-e-d to be of equal length?

/Mats

[CaptainChaos]

hahahahahaha

Tell you what - I'll try both & see what happens!

Ty again ..... please excuse me - Ive been drinking tonight lol

Thinking about it (again) you are probably right lol

[CaptainChaos]

oK .... The plot thickens ....

Thanks for Goldwave - looks good .....

I have done loads of "tests".

If I added 2 seconds to the length (using Time Warp in Goldwave), the sound went wayyyy out ....

So I subtracted 2 seconds from the original length .... still out by a second or so ....

Then I tried minus 4 seconds .... seemed worse ....

Is there a way (without tmpgenc'ing it for 1 1/2 hrs each time) to "test" it quicker?

I'm now wondering whether its not actually gradually going out of synch, but actually "jumping" out at certain points .... If thats the case gawd knows how I'll "realign" it ....

[mats.hogberg]

I'm now wondering whether its not actually gradually going out of synch, but actually "jumping" out at certain points .... If thats the case gawd knows how I'll "realign" it ....

In that case, I'd forget it all, if you're not the masochistic type. If it's jumping out of sync at certain points, there are most likely bad/undecodable video frames at that point, and you're in for some heavy duty cleaning up of your source before encoding.

/Mats

[CaptainChaos]

LOL OK & thank you for all your help .... something else Ive learnt!

Im just going to try to get it as "close" as possible & leave it at that

Thanks again!