Basic audio sync. questions

[payton34]

Hi all,

I am having audio video sync. issues when I capture with my ATI card. My computer system has no problems capturing in perfect audio and video sync. with no dropped frames when I use my Canopus 110 and Premiere Pro. By the way, my computer also does not drop any frames when I attempt to capture analog sources with my ATI card using the HUFFYUV codec. Still however at around the 30 minute mark the audio gets a head of the video by around one second. At this point rather than do the usual detailed description of my workflow I would prefer to ask some basic questions so that I may possibly be able to resolve my audio video sync. issues on my own.

Here are a few of my basic questions:

I capture an analog source to an AVI file using a codec like HUFFYUV or even just a DV25 codec. My ATI software indicates after a 30 minute capture that there were no dropped frames. Why then would my audio be out of sync? Are there other factors at play here?

Also, I read from time to time some people stating that your sound card might be at fault for audio sync. issues. I have a basic Audigy Sound Blaster 24 bit sound card. Why would it matter what sound card I have as it pertains to any audio sync. issues I might be having?

When I use my ATI all in wonder card it does not care how my sound is being delivered to my computer speakers. The ATI card is the piece of hardware that is digitzing the incoming analog audio and video signal, and then form there my software is applying what ever compression format I have chosen, i.e. HUFFYUV. I do not see where my sound card comes into play in the above workflow other than to send the audio signals to my speakers.

Is this correct or am I missing something in the equation?

Thanks,

[vcdforme]

Just a few thoughts.

Why do you believe your ATI software, when it tells
you there are no dropped frames? ATI is just about the
last company I would believe.

Sound cards? Of course they matter.
They all exhibit different amounts of
latency. Did ATI write their software so that
it automatically reads what sound card you have,
then using the proper offset, interleaves the audio
into proper sync with the video?
I think not. Nor do I think they give a shit.

Based on the info in your post....
This is a classic problem of audio card and video not
talking to each other.

[pchan]

You can try AV_IO and huffy or Picvideo MJPEC codec.

[Nelson37]

It is actually your aduio card that is recording the audio signal, not the ATI card. Audio cards have a clock chip, which can be off from the PC timing by as much as 2.5% or more. This can create a cumulative error, resulting in a synch problem. The installation program for the ATI will tell you if your sound card clock is within spec.

There are also issues with the Padding Stream. What exactly this is I do not know. However, I do have some info on what it does. It is apparently used to re-synch the video and audio, and seems to be most used when recording a program interrupted by commercials or otherwise edited. Some playback and manipulation progs use this stream, some do not. WinDVD, version 4, apparently does for playback.

If this stream has any significant size, and the video is processed by a prog which does not utilize it, synch problems will occur. TMPGenc's Merge and Cut feature appears to utilize this stream to correct synch. Many other Mux/Demux programs do not.

[payton34]

Thanks everyone for your input,

Lets see if I learned anything here. It sounds like my sound card is playing a vital role in my captures and any audio video sync. issues.

Using the same computer I have captured with the Canapus 110 converter with no audio sync. problems. Would it be correct then to assume that the reason I do not have any audio sync. issues with the Canopus 110 is because it is essentially a stand alone piece of hardware. Unlike my ATI all in wonder card, is the 110 handling my audio and video indepentdent of my sound card, therefore if I were to have any audio sync problems using the 110, it would most likely have to be the 110 converter itself?

If my sound card is the problem should I be using a different Audigy sound card other than the cheap one I picked up at Best Buy for $24.99

Thanks again,

[Nelson37]

There are a number of users reporting issues with the combination of ATI and Audigy cards. I personally have used 2 such cards with 3 different ATI cards, no issues. Its a crapshoot.

External devices record their own audio, using a single internal reference clock so this issue does not occur. Other limitations and/or issues may, however.

Have you tried MULTIPLE playback softwares, and tested a finished DVD on a standalone player, to check synch? Many software players do not correctly indicate synch condition, most especially on captured files, which are significantly different.

Also, try capping a known good, hi-quality, repeatable source such as a DVD, and do no editing, as a test condition.

[payton34]

Hello Nelson37,

I took your advice and played my 30 miniute captured HUFFYUV avi file on different players.

I first dropped it on the time line of Premiere Pro. Again, by the time I hit the 25 miniute mark the audio was ahead of the video by about 1/2 a second.

I then open the same AVI capture in Micro soft's media player, again the same audio sync. problem.

......However I then opened the same avi captured file in quick time. It had to convert the file to play it but, it played in perfect audio and video sync right to the very end.

Does this mean that I really had no capture sync. problems at all? It was just the players I was using.

Since Premiere Pro cannot play the file with the correct audio/video sync.?.......do I have to be concerned with editing this AVI file on the Premiere Pro timeline, or once I export and convert my project to mpeg2 all my editiing of the video and audio will play in sync. just as the original avi file has played in Quick time?

[Nelson37]

The fact that it converted and played with perfect synch means that everything necessary to maintain synch was already contained within the file. The program that converted it used that information. The other playback softwares did not.

How that will affect various editing softwares, unfortunately, is once again a crapshoot. I learned over the course of several years to basically ignore what most progs were indicating, and only worry about the performance of the final product. That is the only one that matters anyway.

The bad news is that I did find that several softwares wrote their error into the final product, while others did not. I rarely edit other than simple trimming.

[payton34]

Nelson37 and others,

Now am not so sure what is going on. I have tried many other captures with my ATI card using every codec and still as early as the seven minute mark the audio starts playing ahead of the video. Even when I convert the avi file to mpeg2 and burn to DVD the audio still plays ahead of the video.

I am really starting to take a look at my sound card. You mentiond a problem with latency issues with some sound cards.

Here are my questions:

Generaly speaking, if a given sound card was the cause of audio sync. problems, would not the tendency be for the audio to lag behind the video because of a latency issue?


I was on the creative labs site and looked at some of the specs of their sound cards. The card I have has a high latency value as well as a low signal to noise ratio. I am thinking of upgrading to the Audigy 2 ZS card. It has a much better signal to noise ratio and a lower latency.

While capturing VHS video and audio,....Would these better specs of the Audigy 2 ZS sound card give me a higher quality audio recording than my cheaper sound blaster sound card?

Will the the better latency spec possibly resolve my gradual audio sync. problem?


Thanks,