simplest way to sync (offset) audio and video

[kktk1]

I have wmv files in which the audio and video are not in sync.

I have read a number of posts with too many recommendations on how to do this.
Lot of the posts and recommendations are based on quality of the product, speed of encoding and debates over other functionality etc etc.

But it just seems like I would have to download 3-4 programs, do a whole bunch of editing etc to do this.

Assuming that there arent too many other issues(bad video frames etc) and that I wasnt really going for the "best" product, isnt there a simple enough way to simply offset the audio stream slightly to get them in sync?

I can even convert these files to avi and edit them that way and convert back to wmv if that makes it easier.

Thanks
K

[redwudz]

WMV video often uses variable video framerate and VBR audio which makes it hard to convert without sync problems. But if the files already have sync problems you don't have much to lose. If you can convert it to AVI you can add a plus or minus audio offset in VirtualDub, then convert it back to WMV with a different encoder. All those conversions would result in quality loss, though.

I don't know of a simple way, as I don't use WMV very often. But maybe someone here has some ideas.

[Scorpion King]

I don't work WMV any, but I do work AVI quite a lot and simple audio offset is.... simple actually.

Open the file in VirtualDub. click File then File information.

Note the lenght of the video: example 1:00.38
Note the length of the audio: example 0:59.90

You can see by the above example times that the offset is 480ms.

To fix the offset simply go Audio then Interleaving then Audio Skew Correction and enter the 480. Select Direct Stream Copy for both video and audio then save the corrected AVI.

Good luck.

[kktk1]

Thanks....this is easy to use I guess.

But another problem comes up......I noted is that in my version of VirtualDubMod(1.5.10.2), I dont have the Audio menu at all....I have to get to it by going into Streams>>Stream list and do it that way--is this normal?

According to this post I found on the net I should have it in VirtualDubMod----dont know why that happens?

"Since the Ogg Media (OGM) and Matroska Video (MKV) files are container formats, they are only supported by VirtualDubMod and not by VirtualDub. This is why VirtualDubMod differs from VirtualDub in certain aspects, like the absence of the Audio menu. The audio streams from an OGM/MKV file are managed independently, and they are accessed from the Streams > Stream List menu"

Any ideas?

[SDeC]

Note the lenght of the video: example 1:00.38
Note the length of the audio: example 0:59.90

You can see by the above example times that the offset is 480ms.

Not a very good example, because 'offset' time is incidental.

I think King's trying to sketch a VDub operation for you; but you should ignore the bit about shifting streams when there is "offset" listed.

You shift streams when there is sync error. There is NO software that can tell you whether a media file has x-seconds of sync error. Sync error exists when the observer (usually a human) decides, "This doesn't look right."

Regards,

- SD

[redwudz]

I normally use VDMod and I find it easier to use it's audio setup than the regular VD. You go to 'Streams>Streamlist'. Right click on the audio file, select 'Interleaving' and then in 'Audio skew correction', you apply the offset, either negative or positive. The numbers are in milliseconds. 1000ms=1second.

There are two main types of sync errors, the first is where the audio has the same amount of error throughout the video. This can be fixed by applying a offset. The hardest part is to determine how much offset is needed.

The second is where the sync error gets worse as the video plays. This can be fixed by changing the length of the audio or video file so they match. VDM will usually show you the different lengths of the audio and video in the 'Information' page.

Worst case, a combination of both errors, along with missing frames and corrupt video. This can be very hard to correct and involves slicing up the video to isolate each problem and dealing with them individually.

VDM also has 'Scan video stream for errors' under 'Video' that may tell you about missing frames.

I usually convert files to DV format for use in VDM, but that's mostly for editing. Other useful AVI formats are Huffy UV or PicVideo. Huffy and DV create fairly large files. DV is 13GB per hour. Huffy, I think, is similar in size. PicVideo is smaller. These type of AVI formats preserve the quality. Some of the more compressed formats like Divx aren't good candidates for editing.

Applying a audio offset is simple, but all the other stuff is where it can get complicated if you have to deal with conversions on top of the sync issue.

[kktk1]

Thanks folks.

I have noticed(by following these suggestions), that sometimes when I load an avi file, I cant hear any audio in VDM....I can hear audio on that same file using another program..but nothing in VDM....why is that?

These are the wmv files that I converted to avi to fix the audio sync issue.
I used winavi to do that.

K

[redwudz]

VirtualDub or VD Mod is not much of a player, but then it doesn't need to be as long as it works well as an editor. I never notice if the audio plays or not. As long as VD says it has audio and it's in the correct format, it works for me.

It's about the same playing video with VD. It may be jerky or slow, but the same video will play perfectly in a regular software video player. This will be especially noticeable in preview mode with filters applied. I guess it's just not optimized for playback, but I've never seen that as a problem.

[kktk1]

hmmmm...its kinda hard to sync up the audio if you cant hear it :P

I figured out my problem....the avi file had the audio in mp3 format....which VDM does not like?
I rebuilt the avi using PCM format and that worked fine.

K

[Scorpion King]

hmmmm...its kinda hard to sync up the audio if you cant hear it :P

I figured out my problem....the avi file had the audio in mp3 format....which VDM does not like?
I rebuilt the avi using PCM format and that worked fine.

K

I think you need to install the MP3 codec. I installed Lame ACM MP3 Codec quite a while ago and it works good in VD and Mod.

Good luck.

[kktk1]

always someone out there with a solution!
thanks!

I will try this.

K

[kktk1]

I installed the Lame ACM codec, but I still get no audio when the avi file's audio is in mpeg format.
So what am I missing here?


If I create an avi file with audio in PCM format I can hear the audio..

[David K]

Not a very good example, because 'offset' time is incidental

S.D. could you explain more?
What do you mean by "incidental"?
I've never understood what the offset numbers mean, since one can get offset times in files that appear perfectly synched, and as you note, synch is a perceptual phenomenon anyway.

[manono]

I'm not SD, but you can't get the delay/offset just by comparing the lengths of the audio and video. What if the audio ends before the video? Happens a lot.

OK, just what kind of audio is in this MPEG? Have you told us yet? Open it in GSPot and tell us. Maybe all you need is to install the AC3Filter.

And to synch them back up:

Open the AVI in Media Player Classic. Right-click the screen and go Options->Filter->Audio Switcher->check the "audio time shift" box, and fill in an estimate of the amount of asynch. Hit "Apply" and test it out. Negative values are to make the audio play earlier. 1000 ms= 1 second. Resume playback. Adjust until you get it right. At that point you'll know how much the audio is out of synch and how much to set the delay in VDubMod. Then open the AVI in VDubMod, set the Video for Direct Stream Copy, go Streams->Stream List->Right-click the audio->Interleaving->Audio Skew Correction, and set the same delay as you found using MPC. OK your way out of there, go File->Save As, give it a new name, wait a minute or 2, and test it out.

When all done, either uncheck the box or set the audio time shift back to 0 in MPC.

[kktk1]

This is the information I got from Gspot.

Strem Type and A/V interface
Type : OpenDML AVI
I/L : 25 vid frames (1000 ms) Split: Yes

Video
Bitrate : 250 kb/s
FPS : 25

Audio
Name : 0x0055(MP3) ID'd as MPEG-1 Layer 3
Bitrate : 128 kb/s (64/ch, stereo) CBR
FS : 44100 Hz

I downloaded Media player classic, and I can offset and hear audio there from this avi, but cant if I try in VDM. Installing AC3Filter didnt do it either.

[Scorpion King]

When you open the file in VDM what does the program say in File - File Information:

Audio Tag.......... ?
Compression..... ?

The audio tag should say ACM decodable MPEG-1 layer 3 (mp3)
And the compression should be the Mpeg-1 Layer 3 (MP3) compressor (codec) you have installed.

Or at least mine does....

Just a though
Good luck.

[manono]

Yeah, it's not AC3, so that wouldn't help. I wouldn't attach any importance to it not playing, or not playing well, in VDubMod, since it's not really a player. It is used to fix the asynch, but not to discover the amount of asynch.