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Subcap effect lags playback

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Patrick Larsen
Subcap effect lags playback
on Jun 17, 2013 at 8:30:56 am

Hi, i work at a small post production company in Denmark, and we are having a very weird problem with one of our projects in Avid MC. It is a documentary project with a lot of material in different languages, which has been translated to English by a translator using the subcap effect in MC. They did the translation and the adding of subtitles in Sweden, and we recieved the project here (Denmark), to have the editor edit it.

The problem is that whenever the subcap effect track is visible, playback slows down to (sometimes) less than 2 fps. but when we turn the layer off and have the monitor below that track, playback is fine.
I have tried looking for information about it, but it doesn't seem to be a common problem, nor does there seem to be a reasonable solution.

We tried re-installing the OS and the Avid on the computer, but the problem remained. We tried running the project of their own thunderbolt disc, still super choppy playback when the subcaps are on.

The video is transcoded to DNxHD 120, we are running the project of a server (not a unity), that is capable of running DNxHD 120. The computers we tested the project on have these specs:

Mac 1:
Mac OS X: 10.6.8
Avid MC: 6.5 (latest version)
Processor: 2 x 2.8 GHz Quad-core Intel Xeon
Memory: 8 GB DDR2 FB-DIMM
Graphics: ATI Radeon HD 5770 1024 MB

Mac 2:
Mac OS X 10.8.4
Avid Mc:
Processor: 3.4 GHz Intel Core i7
Memory: 16 GB 1600 MHz DDR3
Graphics: NVIDIA Geforce 675MX 1024 mb

The really odd thing is that the Swedish company who made the subcaps say that it works fine on their computer, which is less powerful than our computers.

I find it hard to believe that this is simply a matter of hard drive speed or processors, since we can playback much heavier footage with no problems. Or is the SubCap effect really that rough on the CPU?

I am sort of grasping at straws now, since i can't think of anything more to do, to try to make it playback in real time.

If anyone has tried this before or has an idea of what we can do, any help or suggestions on how to troubleshoot this would be greatly aprreciated.

- Patrick

TL;DR Subcap effect slows down playback to around 2 fps, but when that track is turned off playback is fine.

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Job ter Burg
Re: Subcap effect lags playback
on Jun 17, 2013 at 4:11:11 pm

In my experience it has a lot to do with the combination of available horsepower and the amount of tracks and most of all the amount of subcaps. I have seen slowed down performance as well, and I've always rendered whatever I could render to increase overall performance.

One can only hope that the revised video playback engine in v7 gives us more ease to handle stuff like this.

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Patrick Larsen
Re: Subcap effect lags playback
on Jun 18, 2013 at 9:34:24 am

Okay, that does seem logical, but it doesn't make any sense to me that a two minute sequence with one video track, and one subcap track, would drop frames all over the place.

Would you recommend rendering all the subcap effects, then? i haven't been deling with effects and rendering all that much. Does it keep the render when you shut down Avid?

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