White flashes on screening

[julipe]

Hi there,

First of all, thanks a lot Carl for this amazing software!

I run a University film club and I've been using DOM for years without any trouble. On 3 of our last 5 screenings though, there's been one (or in one instance two) white flash at some point in the middle of the screening. I haven't been able to reproduce it in the theatre yet because it's all one-off screenings and the movies have been deleted right after the screening. If it happens again I'll ask them not to delete and we'll try to reproduce it.

I'm trying to identify if the issue comes from the DCP or the projector (a Doremi DCP 2k). From what I gather looking at old threads here, it seems it could be a frame issue on the DCP? I still have the DCP of the last movie on my computer and tried to play it with DOM's player. I didn't see any flash, but I wasn't present at this screening so my test was based off other people's description of the moment it happened, and they could have remembered wrong. I'm guessing the computer's player might not behave the same way as the projector anyway. Verification doesn't find any problem.

Is this a known issue? Does anyone know how I can prevent it (if it indeed comes from the DCP and not the projector)? Like I said, I've been doing this for years and never had this issue before.

Thanks a lot!
Julie

[carl]

Hi Julie,

Others might have better ideas but my first question would be what JPEG2000 bit-rate you are using. Some systems can do strange things if you get close to the maximum (250MBit/s).

[Carsten]

Use the latest DCP-o-matic player to perform a full verification (incl. datarate checking) (will take sometime).
Is this a SMPTE, or Interop DCP? Verification differs between the two.
Maybe the verifier will find something obvious. As Carl says, some projection systems show such flashes around datarate peaks. But it could also be something that has nothing to do with the DCP itself, but the projection systems hardware, like e.g. cabling or disk issues.

[julipe]

Hello,

Thanks for the answers!

Bitrate was only 150MBit/s (I've actually learned about it in the process and bumped it to 200MBit/s for my next film, hope it won't make matters worse but it still seems far off from the critical rate?).

Those are SMPTE DCPs. Verification was done using the latest version.

My next screening is tonight, I'll see if it happens again and I'll get back to you if there's any new information. It's entirely possible that it's a hardware issue, we're using old material.

[Carsten]

If a SMPTE DCP verification in current player shows no issues, your DCP should be okay. Theoretically, a data transmission error could occur while copying or ingesting the DCP to the server, but, that is very unlikely. Some systems allow to play a DCP directly off a transport drive, which sometimes causes issues. I assume you ingest prior to playout? 150-200MBit/s is definitely safe.

[julipe]

Hi again!

So, I ran into another issue during yesterday's screening: this time, it was two black flashes approximately one minute apart. They lasted for a bit less than a second (felt like more than one dropped frame though). It skipped the subtitle at this very moment too. We tested it again after the screening and the same issue happened. I filmed it if it's any use for a "diagnostic".

Checking it today on DCP-o-matic's player, right at those moments it says "Dropped frames: 1 (error 1)". I've already had dropped frames on the player and it generally didn't translate to any issue that I could see, but I don't remember ever seeing the "error 1".

The DCP is SMPTE, 150MBit/s. I downloaded the very last version (2.16.83) and ran the verification again, no error. We always ingest prior to playout.

Could the drives I use be a possible cause? The problem with the computer in my office is that 1) it's not very powerful, so it takes a long time making DCPs - I usually make them during the night but sometimes I have to work while it runs, I pause, restart, etc, so it's not always super fluid 2) it has very few internal memory so I always encode directly on an external hard drive, which I've read is not the safest way. However I've done this for years with the same material. Sometimes the DCPs fail on ingest and I have to make them again, but I never had any problem once it's correctly ingested/verified until these last few weeks. And if the problem happened during copying/ingesting, the hash shouldn't match anyway, correct?

[Carsten]

If you have continuous access to this projection system, can you try to play the problematic parts again to see if the dropouts always appear at the same playout time?



I never had issues, but I would still recommend to let the encoding run through undisturbed, especially when using external USB drives.

[julipe]

Hello Carsten,

We tested it again and the bug always appeared at the same time.

My next screening is tonight, I'm getting a bit anxious but we'll see if this one runs without problem!

[Carsten]

If they appear always at the same position, you might be able to reproduce these quirks in DCP-o-matic player - they may NOT appear as white flashes there, but maybe as a stuck frame or in the form of other artefacts. That would be a clear indicator that something is wrong with the video file.

[julipe]

Yes as mentioned in a previous message, I checked it with DOM's player and at the moment of the error it says:
"Dropped frames: 1 (error 1)". From my experience dropped frames are not necessarily a problem, but I've never seen "error 1" before. Do you know what it refers to?