Film-Tech Forum ARCHIVE: Film Judder

This is topic Film Judder in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Richard May (Member # 2627) on 08-17-2017, 04:52 PM:

I'm getting what I assume is judder when running either BluRay or off a PC to the projector. The motion is not smooth mostly in panning and movement. Any ideas?

Posted by Frank Cox (Member # 6258) on 08-17-2017, 05:49 PM:

The time that I had that here (it looked like the film was dragging and getting stuck in the projector) the problem was a bad spot on a hard drive that spent too much time re-trying before giving up and moving on to the next data packet.

In your case, it's likely insufficient speed of data transfer from the source device to the projector, which is actually the same problem as I had. The cause is slightly different, though; what are you using to transfer the data from the source to the projector? Are you sure the cables and connections are adequate to the task?

Posted by Richard May (Member # 2627) on 08-17-2017, 06:26 PM:

Going from a computer via HDMI into the GDC IMB. I used a Bluray player with a different movie and had the same effect. Our OPPO decks haven't come in yet so we were using a cheap deck.

Posted by Stephan Shelley (Member # 8587) on 08-17-2017, 07:03 PM:

Do you have the option to use a DVI input on the projector? Those often work better than the IMS/IMB HDMI inputs.

Posted by Richard May (Member # 2627) on 08-17-2017, 07:08 PM:

I do but I would have to reroute the audio then.

Posted by Stephan Shelley (Member # 8587) on 08-17-2017, 07:42 PM:

You should try it for testing purposes anyway. If you look back in other posts on here HDMI inputs are often problematic.

Posted by Richard May (Member # 2627) on 08-17-2017, 08:27 PM:

Just tried DVI-D. Same result.

Posted by Tom Bert (Member # 5719) on 08-18-2017, 04:32 AM:

Are you playing interlaced or progressive?
What framerate is set on the player: could be fractional 23,...

Posted by Marcel Birgelen (Member # 6801) on 08-18-2017, 04:42 AM:

Have you checked alternative content too? Maybe your problem is in the content itself as a result of a previous down-conversion from e.g. 30 fps to 24 fps or 23.976 fps.

Also, when playing from a PC, check the refresh rate of your HDMI output in your operating system. Ideally, it should match the framerate of your content, if that's not possible, it should be as high as possible (At 60 Hz, judder effects should be unnoticeable for average human beings, at least if the rest matches up). Most modern players do have the possibility to set the refresh rate of your output dynamically to match the frame rate of your content, as long as your video card supports it. You want to use this feature, if it works.

In some cases, when playing from a PC, you get horizontal "tearing lines", this is caused by your player not syncing up with the "vertical blanking" of your video card. Most players do have an option for this.

Posted by Steve Guttag (Member # 268) on 08-18-2017, 07:09 AM:

Judder (when motion is not fluid...doesn't require pans can even be people just walking will have a non-fluid motion) is almost always caused by frame rate conversions.

If your source material was originally shot at 24fps and your player is up-converting that to 30 or 60fps it runs the risk of causing judder. When possible, you want to run things at their native frame rate.

Blu-rays are normally pretty good about being able to keep the native frame rate as many consumer TVs are 24fps aware but though many have a 24fps mode, internally they are still ramping them up to 60fps and can possibly introduce judder.

DVDs are almost always frame rate converted to 30fps, regardless of source. Better players, like the Oppo can bring them back down to 24fps and they look MUCH better. Often a DVD/Blu-ray player will have some mode setting that allows one to select "film" or "video" Most are left in Auto, which means the player has to figure it out. Using "film" presumes that the source material was shot at 24fps.

Posted by Carsten Kurz (Member # 5396) on 08-18-2017, 07:17 AM:

Richard - you either have trouble with the natural 24fps motion sequence, which is at the lower end of acceptable temporal resolution for moving images, or, your BluRay Player is set for 60fps output. Check it's setting for HDMI output frame rate or a '24fps'. This may have other names in the player setup.

- Carsten

Posted by Richard May (Member # 2627) on 08-18-2017, 07:53 AM:

I figure when we get the OPPO's, that will correct the issue when using the deck. My bigger problem is playing from a computer (PC). The content looks fine on the computer screen. It's very smooth. Then you look at the screen and it looks like crap. Refresh rate is set to 60hz. I tried the HDMI in on the IMB and I tried the DVI-D in on the projector. No difference. It's not that big of a deal. It would be nice to figure it out for the VERY few times we would run of a PC (like last night).

Posted by Carsten Kurz (Member # 5396) on 08-18-2017, 08:12 AM:

Both deck and PC need to be set to 24fps output rate (or, the PC at 48fps). It is not easy to set up a PC for decent playout quality. A cheap 60US$ Bluray player does better than that. IF you set it to 24fps.

- Carsten

Posted by Jim Cassedy (Member # 4115) on 08-18-2017, 10:22 AM:

quote: Richard May
My bigger problem is playing from a computer (PC).

Without knowing more about your exact setup and the equipment involved,
I can't comment authoritatively about what's causing your problem.

There are several things that could be causing your problem, frame rate
conversions or mis-matches being one of them, as others have mentioned.

But, anecdotally, whenever I've had the issue you describe, it was almost
always a matter of 'computer resources' not being up to the task.

As I've mentioned before in other posts, I often use "Playback-Pro" at
various shows, and I sometimes ran into this problem.

In my case, I went & got a Macbook Pro, with the most memory available,
and replaced the standard drive with one that spins at 7200rpm.- - and I
use this Mac ONLY for video playback, so it doesn't have a lot of other 'crap'
on it. I realize you may not have the time or resources to do this, but I'm
just sayin that once I upgraded and de-cluttered my "playback computer" ,
I've never had the 'motion jidder' problem again. That's what worked for me.

Posted by Richard May (Member # 2627) on 08-18-2017, 10:27 AM:

Yeah, the Macs seem to always play okay as I recall. I may grab someone's mac here and try it.

Posted by Mark Gulbrandsen (Member # 72) on 08-18-2017, 11:20 AM:

Quite literally every one of my SX-3000 customers are using the HDMI inputs for either Ads, Blew Rae, or both. No issues here, it can even be automated.

Mark