View Full Version : FireWire Video Latency Compensation
Sean McCoy
02-11-2008, 02:52 PM
Bob-
Any chance of increasing the resolution of the Frame Advance option to half or quarter frames? The latency on my system sits squarely at a half frame boundary. Not a lot, I know, but I've noticed that Pro Tools and Logic allow for quarter frame adjustments, and I would love to get mine even tighter. (those are on Mac, of course, and I don't know if Windows allows for such divisions)
I guess the SynCheck II came in. :)
It would be cool to have more resolution.
Regards,
MM
Bob L
02-11-2008, 03:42 PM
Well, in reality there is no such thing as quarter frame video sync playback... everything works a frame at a time, as far as I know... but in SS its very easy to simply slide the audio forward or backward anywhere you want in relation to the video to comprensate for latency... you can then adjust to sample resolution if desired.... let's see... how about 1/44100 of a sec offset... that is what... oh i would say a little better than 1/4 frame resolution. :)
Bob L
The problem is that the latency between running picture and sound doesn't fall on full frame boundries all the time. It is a realtime playback issue. You wouldn't want to move audio region position to compensate.
Regards,
MM
Sean McCoy
02-11-2008, 05:16 PM
The problem is that the latency between running picture and sound doesn't fall on full frame boundries all the time. It is a realtime playback issue. You wouldn't want to move audio region position to compensate.
Regards,
MM
Exactly. It's a matter of knowing with total confidence that you're seeing the picture at the right time relative to the absolute timeline, since that is what will be referenced when the audio leaves your studio and goes back to the video editor or DVD author.
Probably unrelated to FireWire latency, but I'm having a sync issue that I'm trying to put a finger on. As soon as I can find some consistency to it, I'll bring this up in another thread.
Sean McCoy
02-11-2008, 05:56 PM
Okay, nevermind the new thread. :o I seem to have discovered, using my cool new Syncheck II, there seems to be a 2 frame difference in latency between 29.97 and 23.976 framerates. :confused: If this is true, it would explain my sync issue. Michael, Dave, Bob, or anybody who might be sending their video out via FireWire, can you verify this? It would be nice to be able to sleep again.
Bob L
02-11-2008, 08:02 PM
You could always adjust and then slip the audio back for the final mix... you can always see the proper sync position by referencing the video on the computer monitor.
This firewire latency is also why I recommend the Overlay method... no latency... even in many HD TV sets now, the UYB, RGB, SVideo and composite signal have a few frames latency when playing an SD video... therefore they are no good for audio sound design... but I have found that in some cases, if you use the PC input of the HD TV (presuming it has one), you can use the overlay out on the second video output of your video card and there is no latency at SD and it also displays the HD better.
Bob L
Sean McCoy
02-11-2008, 09:14 PM
Zero latency would certainly be welcome, so overlay sounds like a good option for my main front LCD when I'm working alone. But I do ADR and Foley recording as well and have to be able to get video out through a video D.A. to a couple of remote monitors, and long DVI runs to LCD's, which would require boosting, would be formidably expensive and logistically impractical. (sure would be cool, though) Can you think of any other way to incorporate overlay into a multi-room setup?
Bob L
02-11-2008, 09:36 PM
Yup... long 100 ft runs work fine when using analog VGA connections... and this will pass HD video perfectly also.
Take the second monitor out of an ATI or Matrox Video card... and then run that thru a video splitter box and you can easily run multiple 100 ft runs using vga cables.
Using the Overlay render mode in ATI Theatre mode or Matrox DVDMax mode, you get full screen video on the second monitor out while your working computer screen lets you edit comfortably in SS.
Bob L
Sean McCoy
02-11-2008, 10:03 PM
I would actually have to send the split VGA signal to both the remote and main front monitors, as it wouldn't be practical for the director to have to watch my editing screen for cues. But I'm sure the quality would be at least as high as the FireWire to S-Video conversion I'm using now. Any advantages to a card with two monitor and one TV out?
Thanks, Bob---this just might be workable. Definitely worth exploring.
sebastiandybing
02-11-2008, 11:03 PM
You can only use 2 of the 3 video outputs, that is how it is working
on my ATI1050 card and also on the ATI1950GT card.
Maybe the Matrox card work differently.
Sebastian
Sean McCoy
02-11-2008, 11:33 PM
You can only use 2 of the 3 video outputs, that is how it is working
on my ATI1050 card and also on the ATI1950GT card.
Maybe the Matrox card work differently.
Sebastian
That may be why Bob recommended using a VGA splitter. That way you can still have the DVI output for your computer monitor and two or more VGA signals for video monitors. Gefen, among others, makes a reasonably affordable VGA distributor.
Bob L
02-12-2008, 02:21 AM
You can get 4 way or more VGA splitter boxes that will easily handle 1920 x 1600 res for very reasonable money... and for video only output, your res on that second monitor output will probably not go that high.
Bob L
Cary B. Cornett
02-12-2008, 06:38 AM
Any advantages to a card with two monitor and one TV out? I assume you mean that you work with two screens now, and that you want the video display out to be independent of both screens. I am not sure that this is necessary. I used dual 17" CRT's for a long time, but when I built my "road rig" I went to a single 19" LCD. My ATI Radeon X300 card allows me to "window" a 2048 x 1536 desktop with a 1280 x 1024 screen. The resulting desktop has TWICE the total space I had with my "dual 17" setup, even though I can't see it all at the same time.
This might seem like a severe handicap at first, but all I have to do to see the "off screen" stuff is roll the mouse over and the screen scrolls smoothly to the area I want to see. Now, if I want to click on something "over there", even with dual displays I would still have to roll the mouse over, so there is actually no extra effort involved. In reality, I work just a little harder, perhaps, but the convenience of being able to work the same way on a remote as at home, and the reduction in hassle with wiring, more than compensates me for this minor inconvenience.:cool:
So, before you pop for a new, more expensive triple-head card, I suggest you try the "windowed large desktop" way of working with a single screen. That way, you can dedicate your second display output to full-screen video.
BTW, if you do try this, I will be very interested in how well it works for you.
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