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Downconvert 720p 23.98 to 29.97 Betacam Problem

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Bill Paris
Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 2:18:11 am

I'm new to the Kona 3 platform and having trouble getting my 23.98 720p clips that reside in a 23.98 FCP project to output to 29.97 Betacam. The manual says the Kona 3 platform doesn't support different video rate cross converts and/or downconverts and when I select the 23.98 all other rates are grayed out. I usually work in 1080p 29.97, so it hasn't been an issue. Any advise would be greatly appreciated!



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Jeremy Garchow
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 2:46:59 am

It works.

Open your KOna control panel. RIght click on the frame buffer and choose 720p59.94. Then right click on your output pipeline icon (such as SDI 1, SDI 2, or Analog component) and then choose secondary, right click again and choose 525i29.97.

Now go back to FCP and make sure your video out is set to 720p by selecting an easy setup with your sequence codec and and the word Varicam in it, such as "AJA Kona 3 720p23.98 ProResHQ Varicam" or similar.

Jeremy




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Bill Paris
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 3:22:18 am

Jeremy,

I think my problem is that I have a true 23.98 rate not the 59.94 rate the Varicam uses for 24p. When I select the 23.98 rate at the frame buffer, I can only select another 23.98 rate in another resolution like 1080 for the SDI out 1 or 2 and Analog. Everything else is gray.

bp



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Jeremy Garchow
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 4:26:34 am

That's okay. Have you tried setting to 59.94 instead of 23.98?


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Bill Paris
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 5:27:07 am

Jeremy,

Ok.... I'm getting though-put now.... I must have had something setup incorrectly. I still need to reconfigure some hardware to get the video into my Betacam deck, but I'm seeing playback with the crops via the monitor so I know I'm getting there.

Question..... do you see the 23.98 motion artifacts diminish after running the 2:3:2:3 conversion in combination with the interlaced SD playback?

Thanks for your help, I'm a little confused about why the 59.94 rate works with the 23.98 source, but I'll take the results for now and figure out the rest later..... thanks again!

bp



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Jeremy Garchow
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 2:58:20 pm

[Bill Paris] "do you see the 23.98 motion artifacts diminish after running the 2:3:2:3 conversion in combination with the interlaced SD playback? "

Can you explain what you mean here? 23.98 is 23.98 and when you add pulldown, you still have 23.98 motion with a few interlaced fields thrown in to conform the frame rate to 29.97. It doesn't smooth out the motion as you would if you shot 29.97 from the get-go. Is that what you mean? If you don't work in 23.98 that much, you will get used to the motion. Going back to base 30 video is quite a shock sometimes.


[Bill Paris] "Thanks for your help, I'm a little confused about why the 59.94 rate works with the 23.98 source, but I'll take the results for now and figure out the rest later..... thanks again! "

Well, I could tell you, but that would require me sending you an invoice, a thorough credit background check of you and your business, and a nice cup of hot coffee, the good kind.

Just kidding!

Very simply, 720p23.98 is a format that is understood by our computers. It is an 'intermediate' format that is stored as 23.98 data. In order to play out 23.98 to most monitors in real time, it has to be conformed to 59.94 (60p) for SMPTE and their rules/standards. So, when you have 23.98 material at a 720p resolution the material gets played out @ 59.94 with standard 3:2 pulldown, although the pulldown is in full frames and not fields. So you have 3 full duplicate frames, then 2 full duplicate frames repeated over and over. This will bring your video to 720p59.94. From there, since you are now at a base 30 frame rate, you can down convert or cross convert to 525i or 1080i. Does that make sense? ALso, when your video is 720p23.98, the Kona cards can take the 23.98 signal and cross convert to 1080p(sf)24 as well as 1080i 29.97 (24p with 3:2 pulldown)

Hope that helps.

Jeremy


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Bill Paris
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 6:30:12 pm

Jeremy,

I guess I owe you at least a good cup of coffee! Thanks for explaining why the 59.94 setting works. I didn't realize the footage was already being processed by the computer so the monitors can display it.... makes sense.

Regarding the conversion to interlaced from progressive, I was assuming the every frame would be converted to two interlaced fields of scanned information.... not just the filler interlaced frames included for timing purposes I'm assuming we see during playback in the 23.98 timeline. Since each frame would be interlaced and scanned onto the screen, I thought this might even out some of the jitter associated with faster moving clips? I have a shot I really like where a giant wave crashed in front of a nice sunset, but I'm getting some motion artifacts as the water explodes into the air..... it's driving me a little crazy since the shot is great otherwise. I was hoping that by converting the shot to interlace from progressive I might be able to smooth out the motion a bit. The other factor would be the pull down settings. From what I've read on the message boards, the best setting would be 2:3:2:3. ?

Thanks for your help....... perhaps I should throw in a danish with that cup of coffee?

bp




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Jeremy Garchow
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 7:51:59 pm

[Bill Paris] "Since each frame would be interlaced and scanned onto the screen, I thought this might even out some of the jitter associated with faster moving clips?"

Oh boy, you asked for it so let the good times roll.

I see how you could think that, but it doesn't work that way as the motion is still based of 24p and with 24p there are no fields and fields account for video like motion as each field as a distinct moment in time, even if the fields that make up that frame are different.

Okay since you now understand how we can see 720p23.98 on a monitor (really, it's 23.98 with pulldown added, so 59.94) we will take this a step further. Now if you were to record that 59.94 stream and look at it frame by frame, you would see that it would be 60 frames per second and have a repeating cadence of 3 duplicate frames, then 2 duplicate frames over and over. Using the ABCD frame cadence reference:

24p= ABCD
24p with 3:2 pulldown in a 60p environment = AAA BB CCC DD with each letter representing a whole frame

So when you down or cross convert to an interlaced 30 frame base band, each progressive FRAME gets mapped to an interlaced FIELD. Alright ... follow me on this one. You are going from 59.94 frames per second to 59.94 fields per second. So essentially each progressive frame gets segmented and turned into a field. Then when you combine those fields in a 30 frame per second wrapper each field follows the exact pattern of the the frames it was made up of. Since you have 3:2 pulldown, it would be 3 fields made up of the 3 prog. frames, then two fields made up of 2 progressive frames, but since they are fields and get combined/played back at 30fps, you have:

24p with 3:2 pulldown in a 30fps environment: AA AB BC CC DD with each letter representing a field.

SO, what the hell does all this mean? This means that the motion characteristics hold up with 24p material when down converting or cross converting. 3 out of every 5 frames are still 'progressive' whole frames, and 2 of those 5 are terlaced but made up the other 3. So you aren't getting any traditional interlacing where every field is a picture from a different moment in time which would equal:

AB CD

Now if you want to make your 24p material look more interlaced, we can talk about motion interpolation plugins that will attempt to recreate fields that are discreet moments in time. For the most part, you will have to retrain your eyes to get used to the motion. Pretty soon, after watching it day in and day out, you will get used to it. then you go back to a true 60i environment and say, "now how the hell can I get this to look like 24p?" And around and around we go.

If you can follow all that, I owe you the coffee and danish.

Jeremy




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walter biscardi
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 8:03:37 pm

[Jeremy Garchow] "If you can follow all that, I owe you the coffee and danish."

You had me at "Oh boy."

Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.

STOP STARING AND START GRADING WITH APPLE COLOR Apple Color Training DVD available now!
Read my Blog!
View Walter Biscardi's profile on LinkedIn


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Bill Paris
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 9:03:55 pm

Oh Boy is Right!

Ok so now we're up to a great cup of coffee.... a danish.... and lunch later in the day!
Thanks for the "pull down seminar"! I'm going to have to reaad this a few more times to get it to sink into my rather thick head, but I really appreciate the information!

Regarding training the eyes for 24p..... I've actually switched to shooting 30psf (29.97) with my F900 and 30pn with the Panasonic P2 cameras because to my eye, the motion artifacts inherent in 24p are too distracting when fast action is involved. I love it for interviews and drama, but for many shots 24p is just too damn jittery for my taste. I guess I've always assumed I could perform a reverse pull down using Cinema Tools if 24p was needed from the footage. (I have not tried this yet, so please correct me if this is not true). I'm primarily a DP with clients that ask for 30psf most of the time. I guess my eye has started to adjust to the look.

Thanks again for the help!

bp




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Jeremy Garchow
Re: Downconvert 720p 23.98 to 29.97 Betacam Problem
on Mar 26, 2008 at 9:08:42 pm

It makes perfect sense, Bill. i know a lot of people who shoot and edit in 30p.

[Bill Paris] "I guess I've always assumed I could perform a reverse pull down using Cinema Tools if 24p was needed from the footage. (I have not tried this yet, so please correct me if this is not true)"

If you shoot 30p, you are stuck with 30p, no removing pulldown will get you to 24p. Again you can do interpolation, but that works better sometimes than others.


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