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TC accurate edits during conversions

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cmlundy
TC accurate edits during conversions
on Nov 13, 2007 at 9:20:15 pm

I'm at a facility that does a ton of work using the the Kona 3. One of the gotchas we're consistently running into are TC accurate outputs when doing any type of conversion with the card. Here's a prime example:

Timeline is 720p 23.98 (DVCPro HD, 8bit, or 10bit, doesn't matter). We need to output to HDCAM at 1080i. So, FCP's playback is set to 720p 59.94 (this adds pulldown to the 24p timeline). Then the Kona is set to cross-convert to 1080i 29.97. The outputs work and look great. The issue is that 9 times out of 10 the output is a field off. If my first frame of picture should be at 01:00:00:00 it may land on that frame, but on the second field instead of the first. Changing playback offsets only moves it an entire frame ahead or back, but it still lands a field late.

What is going on here? Anyone else experience this? I've tried locking to difference references because I'm in a big facility and have a lot at our disposal. All to no avail. Sometimes it works, sometimes doesn't.


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walter biscardi
Re: TC accurate edits during conversions
on Nov 13, 2007 at 9:39:36 pm

This is most likely due to the fact that your 720 timeline is NDF and you're going to a DF format. FCP has never supported Drop Frame in 720p and I have no answer for why or if they ever will, I've been asking for three years.

You will probably just have to shift your edit by 1 frame to ensure that it hits correctly on Field 1 on the HDCAM.

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

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cmlundy
Re: TC accurate edits during conversions
on Nov 13, 2007 at 10:33:43 pm

I'd have to check and see but I'm pretty sure this occurs on NDF outputs as well. The 720p 23.98 seq. is of course NDF by nature. I could see why adding pulldown and going to a DF tape could yield said results in some places, but it shouldn't matter at the beginning of the output, before the first minute. If I insert at 00:59:50:00 (where slate starts) and then at 01:00:00:00 the first frame of picture is off by a field, how is DF involved in that? At that point it wouldn't have crossed a minute mark that skipped any TC numbers. Am I wrong? Under 1 minute DF and NDF are the same.

It seems to me to be related somehow to the the 59.94 (frames per second playback) that then is converted to 1080i 29.97 (frames per second/or 59.94 fields per second) If the Kona 59.94 pulldown out is off by 1 frame that may be translated into 1 field upon conversion to 29.97. Does that make sense? Have you ever seen this, or have you not done this type of conversion?


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JeremyG
Re: TC accurate edits during conversions
on Nov 14, 2007 at 12:22:34 am

[cmlundy] " If the Kona 59.94 pulldown out is off by 1 frame that may be translated into 1 field upon conversion to 29.97. Does that make sense?"

It makes total sense. If you take the 60p stream to make a 60 field stream, each p frame becomes and field (in theory). With the conversion from 23.98p to 60p, then a reinterlace to 60i, then a scale from 720 to 1080, it seems that losing a field is most likely probable. Now can you add one more frame in the beginning of your 60p sequence to 'trick' it?

Jeremy



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Santiago Gutierrez
Re: TC accurate edits during conversions
on Nov 14, 2007 at 6:24:53 pm

I had this exact thing happen to me last week during output. I was working at 1080i and about to edit to tape when the ESPN executive asked me if we could do 720p instead. I said 'sure' and set it up in the Kona Control panel, leaving all the other controls in FCP at 1080i 29.97 as usual. So I did the output and everything went well, then as I was checking the tape, I immediately noticed that it was off by 1 field. This never happens during a downconvert to NTSC or a straight layoff to HDCAM. It was only in this case when I was converting 1080i to 720p on a 1400 DVCPro HD deck. Very strange. I couldn't sort it out and she was fine with it, as they were going to assemble the show in Bristol. But I found it very strange that it was happening in the first place.
Thanks,
Santiago


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Michael Alberts
Re: TC accurate edits during conversions
on Nov 19, 2007 at 4:09:09 am

In our case it seems that 8 out of 10 down converts from 720p 23.98 to SD 29.97 Digibeta is a filed off. Instead of First Frame of Picture starting at 1:00:00:00 it starts a file late. I always thought this made sense since we were converting from an upper field format to a lower field format.
It's disturbing to hear that people are having this issue when doing a cross convert to 1080 29.97. Our same show that we down convert is also cross converted form 720p 23.98 to 1080psf 23.98 and we DON'T have the same problem. It's frame accurate every time. No field issue.
SD deck is an A500 and the HD is an HDCAM HDW-D2000. Locking to house sync 29.97 for the down convert and using Free Run in the control tab for HD outputs.

Michael Alberts
Ambidextrous Productions, Inc.
http://www.ambidextrous.net


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