av sync problem (depsite good hardware)

[fabweb]

Despite my best efforts and good hardware I got a audio sync problem when tranfering my old Hi8 tapes to DV.
I've got leading audio by one second.
Not always, but on more tapes than one...
The tapes are 1997 first generation Hi8 tapes.

I use a Sony EV-S9000, connected via S-Video to a AD converter (a Sony miniDV camcorder with analog in) which outputs a DV signal.
Am I correct that once I capture the DV signal my system (performance etc.) doesn't matter. Capturing with WinDV it shows 0 droped frames. Does this mean I have absolutely no dropped frames or does it means I "just" recorded everything that I fed him and there still might be dropped frames elsewhere?

On the EV-S9000 I use the built in DNR & TBC. I thought I would be safe from audio sync problems.

Any ideas where the problem could be located and how to avoid it?
I have no problem investing more money in new hardware.

[Scorpion King]

If the audio is simply leading (offset) the entire file then it is an easy fix in many programs. I use VirtualDub myself. In VD you enter a value in Audio - Interleaving - Audio Skew Correction. A value of 1000 = 1 second. I would start by entering a value like 400. Thats a little less than 1/2 a second, then go from there until you find where the file will play in sync in virtualdub. Once you find the needed value to sync the file then click Video - Direct Stream Copy, Audio - Direct Stream Copy, File - Save As AVI and type in a new filename. The new file should then play correctly.

If the audio is not simple offset then more drastic actions must be taken to repair it. Sometimes it might be easier to record the audio seperatly then join it to the video portion using a program like Ulead VideoStudio. Tough but a do-able fix. That program would give you the ability to cut up and splice the audio into smaller portions as necessary. I've did it that way before and it will work. It can be quite timely though. There are other ways.

Good luck.

[JohnnyMalaria]

Try using Windows Movie Maker to capture the video (make sure you select DV as the destination type) and see if the files have the same problem.

Also, where does the audio problem show up? If you simply play a DV AVI created by WinDV in Windows Media Player, do you get the delay? What if you send the DV back to the camcorder - is there a delay?

[fabweb]

My audio sync problem was caused by a dropped frame issue.
I thought that when using a DV camera as AD converter I would not ave those problems. Wrong.

My old tpaes had some dropped frames and so the audio and video drifted apart.

I got myself a canopus ADVC 300. This devices duplicetes frames in order to keep the snyc.

And it works perfectly. No sync issues anymore.

[JohnnyMalaria]

I thought that when using a DV camera as AD converter I would not ave those problems. Wrong.

Very true! I have experienced dropped frames in the same manner. In fact, for a given source (e.g., analog output of a DVD player playing a specific DVD), the same frames would get dropped everytime.

[edDV]

WinDV detects lost frames looking at timecode stamps through the process to the file. For DV, lost frames are usually caused when the hard disk becomes unavailable due to OS priority. WinDV attempts to buffer to memory but DV data is coming in a >25Mb/s causing the buffer to fill quickly. The only problem I've seen with WinDV is failure to report a full hard disk or give a warning the disk is near full.

First test is to see if a DV tape captures properly and if audio remains in sync. It should.

In passthrough mode, audio sync is a camcorder and source issue. WinDV has no visibility of source timecode.

I use a ADVC-100 in locked audio mode and have never had an audio sync problem. I've never had an audio sync problem with a pass through DV camcorder either.

If you are dealing with multicamera editing, I always have audio sync problems caused by the ungenlocked camcorders free running at slightly different speeds while recording. This causes audio to slowly drift out of sync as the two files advance. Same goes for an unlocked DAT recorder.

[fabweb]

We are talking about analog video.

My system is set up perfectly. I do not have dropped frames due to a slow hard drive (etc.)

BUT:
(I am writing this for the archives; I learned a lot while researching the internet!)

Dropped frames can also occur when you video is digitized, before the DV signl is sent via firewire to your computer.

Those droped frames will never be reported since windv captures everything that it receives.

So you have dropped frames (which can result in sync issues) which are never reported.

The canopus ADVC takes care of that problem. So if you can afford it, the ADVC 300 is the way to go.

[edDV]

We are talking about analog video.

My system is set up perfectly. I do not have dropped frames due to a slow hard drive (etc.)

BUT:
(I am writing this for the archives; I learned a lot while researching the internet!)

Dropped frames can also occur when you video is digitized, before the DV signl is sent via firewire to your computer.

Those droped frames will never be reported since windv captures everything that it receives.

So you have dropped frames (which can result in sync issues) which are never reported.

The canopus ADVC takes care of that problem. So if you can afford it, the ADVC 300 is the way to go.

True frames can be dropped upstream or during capture. Also true that WinDv won't see these. If WinDv is reporting lost frames, it is a PC issue.

The ADVC is a good capture device and takes measures to maintain audio lock through the conversion to DV format but I am unaware of any feature in the ADVC that will correct audio sync problems originating upstream in the analog domain. It has no way to know if incoming audio is in or out of sync.

[JohnnyMalaria]

WinDV detects lost frames looking at timecode stamps through the process to the file.

That's not entirely the case (you can detect breaks in timecode and report "missing frames"). However, the typical "Captured x frames (Dropped y) z.zz seconds" that most capture tools report rely on DirectShow to report dropped frames. Any DirectShow-based capture utility interrogates a particular software interface to get information about dropped frames etc. Also, for Firewire transfer, DirectShow using the Firewire bus timing for synchronization. Traditionally (i.e., analog capture cards), it uses the sound card's clock for synchronization. My understanding of WinDV is that it is DirectShow-based.

[fabweb]

It has no way to know if incoming audio is in or out of sync.

If the problem is "hardcoded" into the picture (e.g. after one analog copy session) it will not detect it as incorrect.

But the ADVC did a perfect job keeping sync from damaged analog sources (contraire to my DV camcorder/passthrough method).

[edDV]

It has no way to know if incoming audio is in or out of sync.

If the problem is "hardcoded" into the picture (e.g. after one analog copy session) it will not detect it as incorrect.

But the ADVC did a perfect job keeping sync from damaged analog sources (contraire to my DV camcorder/passthrough method).

I'd have to understand that better. If Hi8 plays in a way that frames are lost, audio gets the same time discontinuity (from PCM or linear tracks).

[fabweb]

Good point. I was wondering about that at one point myself. But I focused on solving it by trial and error rather than contemplating about the underlying concept.

I think the sync issue was not due to gradual lost frames but rather because I had "blank" areas on the tape. (back then I rewound the tape, watched it and left some blank buffer before starting the recording again)

This caused a one second lead in audio over video. When I watched the original tape on TV it looked fine, but it wouldn't digitize correctly.

I cannot tell you how it works, but this error was reproducable. Using the ADVC 300 it disappeared. I bought the ADVC for that reason and it didn't disappoint.

[edDV]

Good point. I was wondering about that at one point myself. But I focused on solving it by trial and error rather than contemplating about the underlying concept.

I think the sync issue was not due to gradual lost frames but rather because I had "blank" areas on the tape. (back then I rewound the tape, watched it and left some blank buffer before starting the recording again)

This caused a one second lead in audio over video. When I watched the original tape on TV it looked fine, but it wouldn't digitize correctly.

I cannot tell you how it works, but this error was reproducable. Using the ADVC 300 it disappeared. I bought the ADVC for that reason and it didn't disappoint.

Ahh, now I see. Normal practice would be to start preroll on the active video (after the blank spot). You would loose a couple of seconds that way but the capture would be solid.

[fabweb]

Well, this might be, BUT with the ADVC I can just capture the entire tape without thinking about it.

[edDV]

ok