Drifting Video offset

[seanmccoy]

Originally Posted by Frank Kruse

That said, you will still get different offsets for different codecs, frame rates, resolutions even when everything's genlocked.

The SYNC HD will only prevent the system from drifting and will bring the start error down to sub-frame (near sample) accuracy. The offset however will stay and will be different for every format. There's no way around that.

F.

So with that said, I take it it's common practice to adjust sync offset for projects with different specs, deferring to sync with the video reference mix for confidence?

[smurfyou]

Originally Posted by seanmccoy

So with that said, I take it it's common practice to adjust sync offset for projects with different specs, deferring to sync with the video reference mix for confidence?

Yes!

Hopefully Avid is serious about a lower cost all-in-one I/O interface that includes sync. Will take the SyncHD out of the picture for smaller rigs.

[seanmccoy]

Originally Posted by smurfyou

Yes!

Hopefully Avid is serious about a lower cost all-in-one I/O interface that includes sync. Will take the SyncHD out of the picture for smaller rigs.

So does everybody pull out their Synchecks between each project, or do you just eye it?

[Schottlandru]

Originally Posted by seanmccoy

So does everybody pull out their Synchecks between each project

THIS! I usually check by eye (mixing/premixing for example) but if I am editing foley/ADR or sound design to picture, I check.
Also after lunch/breaks.

Why this changes I do not know. Without bringing up bashing - Nuendo is consistent, as is the OS video playback. Not a 3 frame span that is clearly visible.
So I wonder what is causing the issue internally with PT - and why would a Sync HD be needed to get the computer to ouput its video and audio streams at roughly the same time. LCD frame offset etc aside... something is wrong in the internal pipeline for sure. And it seems like a different pipe after every session load...

(And I have been to several studios and edit rooms out of house where there are no Sync IO/HD and it is stable and seems consistent throughout. +/- the quarter frame as listed.)

[Schottlandru]

Just came back from lunch break to find that PT video offset in the open session had shifted 90ms over lunch break.

[Fish Horse]

As Frank wrote, only a genlocked system will be 100% accurate when offsets are setup correctly. The big downside of a genlocked system is that a connected PT SYNC unit introduces additional latency when you hit play. Very annoying.

[Schottlandru]

@Fish Horse - it seems to be a different issue. This used to be better in older versions, i.e. one offset for one project worked (actually for one codec for all projects). For me it was 35ms.
It now changes on every re-open, or even over breaks. From -50 for example to +80. And stays at that (+/- 20ms)

I am not talking about slight drifts of 1-2 frames on each play. I have +/- half a frame. I'm talking about actual variations of 4 frames for every time a session is reloaded. Once loaded, THAT new offset stays constant until next load (except for lunch breaks).

I am thinking this might have to do with some kind of power-saving issue of an idle system too, due to it cropping up over a longer break.
Still trying to track that down...

[smurfyou]

I don't experience that. Once I find the offset for a certain codec and format it's consistent.

[Schottlandru]

Originally Posted by smurfyou

I don't experience that. Once I find the offset for a certain codec and format it's consistent.

Yes that's the frightening thing, used to be the same here :-\ Different settings per codec / frame-rate but consistent.

At first I thought it was because of me working through an input-monitored re-rec track (and had the Auto low-latency off setting deactivated in the mixer for that track).
But it happens in a plain edit session with hardly any CPU taxing (25%ish), no re-rec bussing too.
Something has been screwed up and the OP post seemed like a similar issue.

[Schottlandru]

Just an update on interesting findings:
I think it may be linked to processor Speed Stepping (EIST for Intel i.e.).
These I usually have disabled (re DAW OS optimization), but it seems that when they are enabled while loading PT or a PT Session, they throw off the internal latency calculation.
Have to delve deeper into this but I have been pretty consistent with offset values for this one session now over the last week - always making sure I have my right CPU profile loaded when opening PT/session.
Other things I have done also: changed PhysX away from NVIDIA GPU to the CPU and disabled some of NVIDIAs "auto" choice on which GPU does what etc.
Might have been a combination of things.

Hope it helps the OP or others...