Broken Video? Send it to Tape!

This is of no importance whatever, but I'm just curious why it's happening. Mac Dual G5, Panther, FCP 4.5HD (remember that?) and a very nice AJA IO connected to the machine room. All aggressively Standard Def. All soon, hopefully, to be blown away for a nice Intel machine with the latest FCP, etc.

It's a given that any time we have video with interlace problems, bad horizontal motion, gross lines across the picture, etc, etc, the only way to cure it it to send it to the machine room and record it onto one of the DigiBeta machines. Then capture it again and all the problems are gone.

Poof.

It's never been known to fail. It's the video Get Out Of Jail card. We keep a scratch tape in the machine room and that's all it does. We spent weeks once trying all sorts of other cures and conversions and patches and exports. etc. etc. etc. Nothing. Nada. Zippo. We would just exchange one set of anomalies and damage for another.

"OK, the lines are gone, but now the picture buzzes when somebody moves..."

Then somebody noticed that video on tape from the Flames, Infernos and Avids never did this. So we tried it -- we made a tape from the damaged video and pulled it back in again. Son of a sea cook if it didn't work!

We don't deinterlace at any time and the final video still clearly has interlace in it -- the shows all go out at 29.97, but it's the difference between video you'd be willing to show somebody and garbage.

Koz

Is it possible that it's your capture card correcting the mystery problem? When you see the interlacing/motion problems, where are you seeing them?


www.derekmok.com

Where is this video coming from? If it is so badly interlaced and full of horizontal movement, how are you outputting this to tape WITHOUT all of that as part of the image? Why does it suddenly vanish when you output to tape?

How are you monitoring all of this?

I'm sorry, but this sounds like user error...because I haven't heard of this. Plus that is a very old version of FCP...was it designed to work with the IO? (hmmm....maybe).

Stilll...you see those issues, yet play out to tape and don't have them? Smells fishy, like that sea cook didn't cook the food long enough.


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<<<Is it possible that it's your capture card correcting the mystery problem? When you see the interlacing/motion problems, where are you seeing them?>>>

Almost always stuff we got from Somebody Else. One of our jobs arrived as Apple ProRes 4:2:2 720:486 video files. It looks dreadful on the Viewer, it looks dreadful on the Canvas at any size including 100%, it looks dreadful on an attached glass NTSC monitor and it makes a dreadful DVD.

Off to tape with you. Problem gone. It's like waving an 83 pound magic wand.

Some fraction of this artist's work does that and some fraction doesn't. Some clips showed up as 16x9 and some 4x3. Both machines do it on the same cuts, the other Dual G5 has FCP 5.0.4 and the AJA Kona II.

Some of the work looks perfect everywhere under all circumstances. Still clearly NTSC and interlaced. Those drop right into a timeline, Studio Pro, make a DVD and go home.

This is just one client, but it happens all the time on and off.

I'm thinking about this as I write. Are we looking at field reversals? The computers don't give a fig where the fields are, but the tape machine is a fanatic about it.

Koz

> it looks dreadful on an attached glass NTSC monitor and it makes a dreadful DVD.

And what's the signal path on the NTSC monitor? I assume you have a central machine room where you do the tape output, but the monitor on the individual stations isn't hooked up to that pipeline. Which makes me suspect that a) either the individual stations have something wrong with the way they're set up to view the video signal, or b) there's something in the central machine room's tape-output pipeline, some piece of hardware that's correcting the problem.


www.derekmok.com

There is a glass NTSC monitor on a stand-alone DVD player. That's our Quality Control point. Each Mac has a glass NTSC monitor connected to the monitor point on each capture card, IO in one case and Kona II on the other.

I did not look at the damaged video as it was being sent to the machine room and I didn't inspect the tapes after the last cycle of correction.

I can do that tomorrow.

Gotta be fields. There are only two states in the clip. It's either suitable for air or the dumpster. There is no subtle variation.

Koz

I'm also thinking field order. What it doesn't explain is why the stand-alone stations, with the same capture card and broadcast monitor, doesn't play it back okay. Have you already compared the Kona Control Panel settings? What about how the card connects with the deck in the machine room vs. how it connects with the monitors at the stations?


www.derekmok.com

Is it the difference between 720x486 and 720x480? That would reverse fields.


Adam

> Is it the difference between 720x486 and 720x480?

Where'd you get that? These frame sizes would be NTSC. In NTSC land, it's always Lower First.


www.derekmok.com

ONly from ONE client that you have this issue. Then the issue is caused by that one client. This isn't normal. Dunno how you solve this by going to tape...I'm not enough of an engineer to figure that out. But the client is doing something screwy, and instead of slapping a band aid on the wound, or treating the symptom, why not look at the cause and figure it out?


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If you run 720x486 video through a process (like compressing for DVD) that is expecting 720x480 source material instead of 720x486, the frames will become reversed and you will see interlacing artifacts.

Try it yourself if you don't believe me.

Also, if you edit 480 material into a 486 timeline, FCP automatically sets the center point to 0,1 to account for this difference. The reverse is also true.

Maybe what he is seeing is a result of something like this.

What sequence settings are being used?

A

> If you run 720x486 video through a process (like compressing for DVD) that is expecting
> 720x480 source material instead of 720x486, the frames will become reversed and you will
> see interlacing artifacts.

Compressor can make a mistake interpreting field order on an Uncompressed SD file in the Automatic setting, but a) it doesn't happen all the time, and b) you can get around it by setting the Field Order to Lower instead of Automatic. It still doesn't explain why he sees the problem on the station's own capture card-broadcast monitor combination, and why the problem disappears once it goes to tape. Any field-order issue in the source file should end up on the tape itself, and that's the mystery.

He doesn't see it just on 720x480 DVDs. He sees the problem by playing source file in the Viewer played through a broadcast monitor, using a 720x486 ProRes file. So unless he was using 720x480 viewing presets (unlikely, since they're working at broadcast and going to DigiBeta), it doesn't look like a likely suspect to me.


www.derekmok.com