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Sound and Video not matching up

Discussion in 'Multimedia, Projection, and Show Control' started by MHSTech, Nov 16, 2007.

  1. MHSTech

    MHSTech Active Member

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    Tonight I went to play a DVD on our video system. As I was playing it, I noticed that the audio was a second or so ahead of the video. What causes this? What can be done to fix it? We have a VP-25xl presentation switcher from Kramer, and they it gets sent to a distribution amplifier (also a Kramer) to all of the TVs and projector.
     
  2. icewolf08

    icewolf08 CBMod CB Mods

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    Did you try the DVD in any other player? It is possible that the disc is defective. Did you try a different DVD in your system, is the problem isolated, have you had it before?
     
  3. Raktor

    Raktor Active Member

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    Try a different DVD player, different DVD, hooking up headphones or small speakers directly to the player, hooking up a small TV to the player, etc.

    You don't have a delay set on any amps do you?
     
  4. kwotipka

    kwotipka Active Member

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    This is quite common in video rigs. First, play the DVD on a player that is directly connected to a NTSC (not computer) monitor. Make sure that it is not an issue with the DVD. Sometimes, DVDs that come from "pro-amateurs" have some sync issues so rule that out first.

    Commonly, the video delay is caused by the time it takes to process the NTSC signal into hires, scaled video. Depending on the speed of the internal processor, it can vary from model to model. The way it seems that this one works is to process anything that is not highres before it sends it to the output. Sorry but there is no way around this. It is doing lots of things here that need to be done technically. If you want a more detailed example, let me know and I can get into the grit of the matter.

    Normally, we put audio delays on the devices and slow them down just a bit. Usually this is no more then the 1/30 of a second delay caused but the box. If it is more, then there may be some other issues.

    kw
     
  5. SHARYNF

    SHARYNF Well-Known Member

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    You need to check the frame delay specs on your Kramer switcher, If for instance it allows you to switch seamlesly un synced sources, it will have at least one frame delay sometimes two frames. Projectors especially dlp will usually also introduce a frame delay, each frame is 1/29.97 of a second. to keep things in sync you need to get an audio delay which will allow you to add the frame delays.

    Where this can get to be an issue is if in stead of video you are using a feed froma camera thru a switcher do a dlp projector in a live situations, here you are sort of stuck, you cannot delay the audio unless ALL of it is pre recorded.

    Fun fun fun, a lot people cannot detect a single frame delay, more can detect a two frame delay and most can detect 3 or more frames

    Sharyn
     
  6. MHSTech

    MHSTech Active Member

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    Thanks for the responses. The DVD isn't the issue, it worked in another DVD player and TV when we watched it earlier this week. It can from a TV station (WTVG) too, so I trust their work. I haven't tried another DVD player with the system, but my guess is that it was something in the processor. We had never had this problem before though.

    I would like some more details on this. There is also an option to bypass the highres on the output. I don't think I tried this yet.
     
  7. kwotipka

    kwotipka Active Member

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    Well, I am not too sure why you haven't noticed it before. Unless something is really going bad, it should have been there any time you use the switcher and it has to upscale the signal. By upscaling, I mean it is taking the NTSC analog composite video or component (Y/C or R-Y,B-Y,Y) and converting the approximately 720x480 (I said approximate don't no one go getting all picky or I'll have to start a new thread on resolutions) and upscaling it to 1024x768 which is the popular projector standard. It *may* also be converting the scan rate and other voodoo for you as well. One thing you can do is set your output scan rate to 60hz as this is the closest to NTSC video. If you are running the projector at 70hz or some other freq, you can see where the scaler is doing more work then it probably needs to do.

    If you are playing back from a computer or other hires source, then it does not have to be upscaled and is passed right to the output (as quoted from the company's website). So, in a nutshell, anything that is not whatever the native output resolution of the switcher/scaler will have to bescaled / converted.

    Also, the other poster is right that DLP's insert a bit of the delay due to the way they work. Another thing is that you *can* put delays on the mic lines provided all of the stars and planets align and you are in the perfect situation. I wouldn't count on this 99.9% of the time though cause it is pretty dang ugly for the person having to do the speaking. I am hoping that as processing speeds of the scalers get faster and we move over to HD sources that require less horsepower to process, this issue will fix itself.

    Most of the time, unless there is something like a talking head in the video, most people will never notice it.

    So, here are a few options:

    Put an audio delay on the source (DVD, VHS, DVCAM, whatever is not native 1024x768 RGBHV).

    Convert your media to some sort of video file and play back from the computer. Test this first because now the computer is having to do the upscaling and they don't always look good. Remember you are taking a 720x480ish signal and bumping it up to 1024x768. To keep it looking the best, it needs to be played back at it's native resolution. For example, if you have some miniDV footage, then it will play back at 720x480 which as you can tell is not "full screen" (1024x768). You can set some players so that they play in a window or you can embed it into something like power point. Another thing that puts a hit on quality is image compression. I find that a video from a DVD (MPEG2) looks horrible after the compressed image gets processed yet again in the scaler on it's way to 1024x768. Again, quality varies with the quality of the encode but just like audio, encode->decode->re-encode doesn't work so well. True, most of your digital formats such as miniDV are compressed but not as bad as DVD.

    Check to see if the devices you are using can be gen-locked. This helps by bringing everything into time and you might makeup a few ms of time. I do this whenever possible because I can then switch sources in pip windows without them going to black in between to resync. This won't be possible with a consumer DVD player and I don't know if they even make a genlockable DVD player.

    As far as media goes, my preferences are in the following order DVCAM, BETA-SP (cause the machines are tanks),DVCPRO. I try to steer the clients away from DVD whenever possible.

    Now, if you are working with HD sources and HDSDI signals, this is a totally different story. Most of those native resolutions are well above the 1024x768 and you are actually scaling down the video. Of course if you have HD video to work with in the first place, then you most likely will be using HD switchers and projectors as well.

    Hope this helped you out and didn't confuse the issue.

    kw
     
  8. museav

    museav CBMod CB Mods Departed Member

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    Was it really a second? I can understand a few frames from processing but a full second is a little extreme to be just processing related. And if it was related to processing the DVD output, one would think that it would be consistent and be related to the device, not the DVD itself. Also, the VP-25xl apparently has no audio delay available, meaning that can't be used to help you but it also can't have changed to cause the problem.

    Prehaps there is some video delay inherent in the video production that when direct viewed on a CRT isn't readily apparent but that when combined with the latency in your presentation system becomes quite apparent.
     
  9. MHSTech

    MHSTech Active Member

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    I may have been exagerating it a little bit when I said a second. I'm beginning to think there may have been some issues in how they put the DVD together, since it has appeared to be unique to this DVD. I will find more out next week when I dive into the issue.
     
  10. astrotechie

    astrotechie Member

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    If the problem appears to be with the DVD, then the problem is from the people you encoded the DVD. If you don't match the audio sequence to be in line with video sequence, then you will have a problem with video delay or no video, or no audio, or audio delay. Also another problem could have occurred when the DVD was burnt. Another possibility is that you were using a video scaler and that made something happen. The worst case possibility is that there is a problem with the DVD play proc. and that means the player is defective. There is nothing in how you establish a DVD, if it is in NTSC or PAL. The matter is in the arrangement in the program that it was edited in. Also another problem is a delay in the sound system.

    I'm a volunteer for WPMC. I have worked with Avid Media Composer, Adobe Premiere Pro, Sorenson Squeeze, and Adobe Creative Suite 3. So it isn't the problem in which format it is in (NTSC or PAL[the difference is the ratio]).

    I hope that helped a little bit.
     
  11. kwotipka

    kwotipka Active Member

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    I am curious about how this turned out. Was it a problem with the DVD or was it a combination of DVD and scaler delay? Sometimes when novices and even professionals start working with digital media, the don't understand how things like changes in sample rates can cause a/v to get out of sync. This usually shows up as the video slowing becoming unsynced with the video as time progresses.

    In the future, if you have these types of issues and you don't have an audio delay to work it out, have the person who is producing the video slide the a/v out of sync by "X" frames. Yes, this is an ugly way of doing things but it will work.

    kw
     

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