Video Sync Offset jumps

[simonchase]

Hi All,

I'm using Syncheck II. I'm outputting video on my intensity pro.

The video sync offset feature in Protools only seems to work in full frame chunks. That's to say it has no effect for 3 increments of "One quarter frame" then it leaps to a full frame change.

Here's what I found:

-2 quarterframes - 1 frame and six sixteenths (audio Ahead)
-1 quarterframes - six sixteenths (audio Ahead)
0 quarterframes - six sixteenths (audio Ahead)
1 quarterframe - six sixteenths (audio Ahead)
2 quarter frames - 10 sixteenths (video ahead)
3 quarter frames - 10 sixteenths (video ahead)
4 quarter frames - 10 sixteenths (video ahead)
5 quarter frames - 10 sixteenths (video ahead)
6 quarter frames - 1 frame and 10 sixteenths (video ahead)
7 quarter frames - 1 frame and 10 sixteenths (video ahead)
8 quarter frames - 1 frame and 10 sixteenths (video ahead)
9 quarter frames - 1 frame and 10 sixteenths (video ahead)
10 quarter frames - 2 frames and 10 sixteenths (video ahead)


Any clues anyone?

[Postman]

That's the way it works when video goes through video hardware. It is not a Pro Tools limitation so much as a fact of life with video signals through video hardware. The best way to deal with it is to get speaker audio ahead of video by a small amount, consistently the same amount, then delay the speaker audio just enough to make up the difference (with a plugin or external delay hardware).
Same thing happens with MojoDX and with a video satellite.

The excellent consistency you show proves that your system is syncing flawlessly! Check it during heavy audio processing and automation to be sure you've got the best 1/4 frame value. PT's 1/4 frame increments sometimes need to be tweaked + or- one digit to get 100% consistent results.

[dford]

The video sync offset in Pro Tools does work in 1/4 frame increments as designed. I think you'll find the fault in SynCheck. I have used both SynCheck II and SynCheck III and the results vary.

To be fair, the SynCheck manual states that digital video has a "span" which can change the delay with every play/stop command. Professional signal paths and gear might see a 1/4 frame to 1/2 frame span on each play/stop command, whereas a consumer setup could include up to a 1 frame span (and more in some cases).

If this variance is not what you are used to see, check the batteries. The batteries on the SynCheck are very sensitive to voltage changes, they should be checked often. I even found a power supply that I wired to a 9V battery clip to provide a constant voltage. That at least helped me trust the tool every time I use it.

Good luck, I hope some of that helps.


Dev

[cananball]

Avid Mojo quicktime offset is adjustable by quarter frames
Avid Mojo "Avid Video" offset is adjustable by full frames
Blackmagic Video cards only adjustable by full frames (quaterframe adjustment might be available in Pro Tools but BM card can only resolve full frames)

[dford]

When you make a change to the video sync offset in ProTools, it moves the video file up and down the timeline by the adjusted amount. Then the black magic receives video frames from the GPU at the encoded frame rate and plays out to your display. Therefore ProTools can indeed make order quarter frame adjustments.

If you're referencing your black magic card, it could be possible that the video is trying to align to the frame edge. That said, I do not believe the intensity pro card has a reference input.

Dev

[Frank Kruse]

In PT11 the sync offset window says that when your card is gen-locked (and your PT via sync HD) any entered offset value will be rounded to the next full frame.
Even though you can now enter ms and qf.

I just did a quick test with my Intensity SDI genlocked. The sync is much tighter and less jittery than with the Intensity pro but it's not possible to narrow the offset down 100%. I can get it down to 6-10ms of stable offset and then do the fine-tuning with my digital board which luckily has a delay on every output bus.

10ms is very good. even moving around your room could introduce more delay so I wouldn't get too obsessed with getting it down to 0ms and no jitter.

Lets say you get a reading of 59ms on the Syncheck with 0 offset. In theory you would enter 59ms in the offset window. If I do that I get a reading of around 6-10ms depending on where I measure. 10ms using the line-in instead of the mic at my listening position, which is strange because it's actually more than in front of my center speaker.

You'll never get it stable with an Intensity pro or any other non-genlocked card, BTW. Get the BM SDI card it's almost the same price as the Intensity pro plus one of these cheap 35€ SDI to HDMI converters. No need for a 200€ box for that. For editing purposes it works like a charm.

You will need a sync hd btw and a common tri-level clock to get as close as possible.

Frank.

[Postman]

My mistake, yes Intensity Pro has no reference in. Not sure why I was thinking of referenced SyncHD and DeckLink. Frank's right the sync will not be stable until you get a genlocked video output, AND SyncHD.

[simonchase]

Thanks all,

It's not the Syncheck because i can manually move the audio quarter frames and see the results on the Syncheck. And, as been pointed out, the intensity pro has no clock in, so shouldn't fall foul of the warning on the video sync offset window (in theory).

I am very pleased with the lack of drift though. I'm getting way more consistent results than ever before now I'm in PT11.

Nearest half frame will have to do with this set up I guess.

And I'll take the opportunity to add my voice to the general bemoaning about AVID being unable to provide a simple video playback solution for Pro Tools users that just locks solid any quicktime.

[Chief Technician]

Originally Posted by dford

When you make a change to the video sync offset in ProTools, it moves the video file up and down the timeline by the adjusted amount. Then the black magic receives video frames from the GPU at the encoded frame rate and plays out to your display. Therefore ProTools can indeed make order quarter frame adjustments.

I'm not certain that this statement is accurate. Someone on Avid's payroll (name withheld to protect the guilty) told me that with Pro Tools v10 and earlier, QuickTime playback is provided by the QuickTime engine, which they refer to as a black box. When you press play in Pro Tools, it reads a video frame from your movie and sends it to the black box (QuickTime engine). The black box eventually passes the video frame out to your playback device, then tells Pro Tools "I'm ready for another frame". The thing about this black box is that it doesn't always stay locked to video ref, if ever. Essentially the black box that is QuickTime playback is always susceptible to +/- .5 frame of slop.

This should be different with Pro Tools v11, though I have not done any testing with v11 to confirm this.

[dford]

Originally Posted by Chief Technician

I'm not certain that this statement is accurate. Someone on Avid's payroll (name withheld to protect the guilty) told me that with Pro Tools v10 and earlier, QuickTime playback is provided by the QuickTime engine, which they refer to as a black box. When you press play in Pro Tools, it reads a video frame from your movie and sends it to the black box (QuickTime engine). The black box eventually passes the video frame out to your playback device, then tells Pro Tools "I'm ready for another frame". The thing about this black box is that it doesn't always stay locked to video ref, if ever. Essentially the black box that is QuickTime playback is always susceptible to +/- .5 frame of slop.

This should be different with Pro Tools v11, though I have not done any testing with v11 to confirm this.

Hey Chief,

I think we are basically saying the same thing...In a previous post I mentioned the "span" that is inherent in any digital video playback too - So I agree a variance will always be detected to some extent


Dev