Framing changes with framerate

[Jon Dent]

Noticed an interesting issue with our SX2000A/NEC1200 setup. When displaying flat material at 24fps everything looks properly aligned on the screen, however when I attempt to play 30fps material, the image shifts noticeably to the right by a few feet, leading to an off center image (we have a scope screen with no masking). No lens adjustment are made when the framerate changes, so it appears to be a software issue somewhere.

Has anyone else seen this kind of issue, or know how to solve it? Ideally I'd run everything at 24fps but the judder from converting 29.97fps commercials to 24fps drives me up a wall so I'd prefer not to do it.

[Steve Guttag]

The SX2000A only supports 24fps and 48fps, as I recall. The SX-2000AR supports 30fps (and 60fps). If my suspicion is correct, that is where your image shift is coming from. The only two frame rates that were part of the DCI spec were 24 and 48 so "legacy servers" may only support those (e.g. the Dolby DSS100/DSP100 would also be restricted). Later servers supported 30fps and then 60fps. A few now support even higher rates (e.g. 120fps).

Odds are, there is nothing you can do about it unless GDC had a firmware update that added 30fps capability. You can't fix it in the projector because the image is shifted in the mediablock so the timing is going to be off. You might be able to make a Flat image center via the projector but Scope is likely to just get cropped off.

How's Digi-Key? That's is the thing I knew that came from Thief River Falls!

[Jon Dent]

Seems odd that it would play back at all if it didn't support it. It's running fairly old firmware (7.83). Not sure if there's a reason or just that nobody bothered to update it yet.

Digi-Key (and electronics distribution in general) is hoppin' crazy. They're letting cushy work-from-homers like me volunteer time in the warehouse to meet shipping demands. That's cool you recognize the name.

[Carsten Kurz]

I remember a special option that Carl had to re-implement in dcp-o-matic that allowed older GDCs to play back 30fps IF the container was set to a smaller non-standard type (If I remember right, 1920/1080). The reason to put it back in the application was that some users were not able to play back 30fps content in regular flat containers, and the conversion from 30fps to 24fps is indeed an ugly one.

[Marcel Birgelen]

Is it DCI material you want to playback or something different? Because if the source isn't a DCP, you could try an alternative player connected to the DVI port of the projector. That should support 60fps, which is supported by most media players, which in turn would work fine with 30fps source material. Before delivering commercials as DCP was more common, we used such setups to play digital commercials in all kinds of wacky formats and framerates, including 25fps, 50fps, 30fps and even some in 60fps. We just ran the output at 60p. While not 100% ideal, the upconversion was sufficiently smooth as not to cause any detectable judder or other irritating artifacts. We were happy if we did get something that was non-interlaced and came close to full HD without an awful amount of compression artifacts.