Alchemist conversion 23.98->29.97

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23

Unless we’re talking about sports, interlacing should be all but banned, like an old disease eradicated by vaccines

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24

Ah Chappie. It’s boring eh.

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25

I’ve always been curious about the magic “motion smoothing” hardware conversion that I always turn off everyone’s TVs… Could be handy to have that algo in your back pocket to shitify some 23.98/24 footage…

26

It is terrible but isn’t the tv signal delivering fields even on progressive frames or is that old CRT tech?

Interlacing used to be a good solution I thought. Trouble with the advent of digital is how bad those interlaced frames look when your playing your mov back at half size and the fields become stripes.

27

Yes, it’s holdover from CRT technology but also from the limited bandwidth for over-the-air broadcasting

28

I’m so sorry I missed this thread back in March. I have l lots to say but all of it is covered here. Good to know I’m not going mad and we all agree. I’m saving this to quote to my producers next time (likely imminent) this problem raises its ugly head. Love you all.

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29

Hello all

I know this is an old thread, but I have a related question.
Our final delivery will be at 29.97fps, but DOP wants to shoot at 24fps. Am I wrong to think we should insist to shoot at 29.97 as that will be our final delivery and avoid headaches? I guess not all the TVs in US would accept pulldown as a way to get to 29.97? I really would like to avoid retime if we can. Any suggestions?

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30

Basically, it was all based on power line frequency. 59.94/60 cycle power.

31

Strictly speaking, I’d say you’re correct.
If the delivery is 29.97, they should shoot 29.97.
Unless they want deliveries at both at 24 and 29.97.

But…why on earth are they delivering at 29.97??
I can only think of a couple very specific scenarios where that would be required.
Is it possible someone has an outdated spec sheet and they don’t really need to final at 29.97?

The problem is that it’s very to easy to go from 24 to 29.97 and extremely difficult to go from 29.97 to 24. If there’s a chance they’ll need a deliverable at 24, then it’s safer to shoot at 24.

If they’re certain they’re finishing at 29.97 and the DP insists on shooting 24, try to get assurance ahead of time that they’ll accept a continuous 3:2 pulldown or frame-based timewarp.

-Ted

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32

Based on my lifetime of dealing clients holding spec sheets, I would bet a lot of money on this being the case.

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33

Wellllll, not necessarily.

Some companies* make devices that refresh at base 30 and whose interfaces animate at base 30. Some have a lot of live television event infrastructure built around base 30. Some have website backends that prefer base 30.

When DPs, hypothetically, insist on shooting 24 it creates a tremendous number of problems for some very nice people.

Andy may be right, it’s probably a dumb line in a spreadsheet that no one has ever double checked. But it also might not be. It’s worth asking.

*I mean, or so I’ve heard.

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34

Also, and I don’t mean this sarcastically, good luck insisting to your DP that he shoot at 29.97. The only time my heart rate alert has gone off on my watch was when I engaged in a similar discussion during a semi-recent pre-pro.

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35

Well said Kirk. In my experience, nothing bad ever happens when you shoot at 23.976 and nothing good happens when you shoot 29.97

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36

That is actually not what I’m saying. Lots of bad things happen for me personally when cameras roll at 23.98, but my situation is specific, and turning material into 29.97 from 23.98 is less trivial for me than it would be for most other folks.

My point was that it might not hurt to ask, given that my situation is so staunchly pro 29.97 and folks regularly assume that it’s not a big deal if they just casually ignore that requirement.

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37

Ack! I fat-fingered my response @Kirk. HEARD.

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38

Thank you so much for all the replies gang. Very helpful as always.

39

30fps

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40

ok wait i am getting confused with the tv specs for the US (i mean who wouldnt)

so here in europe its very simple.

  1. You shoot at 25 Progressive

  2. you finish in 25 progressive

  3. You or the distributor converts 25p to 1920x1080 50i(peach wants 50i, adtoox takes 25p)

where field1 and field2 are from the same progressive source so you just take the 2 fields and merge them and get a perfekt reconstruction of the 25p master.

But what goes “over the air” is still 50i. or rather “25psf”

ok now to ntsc;

Option1)

  1. you shoot at 23.9 progressive

  2. you work in 23.9 progressive

  3. Now here it seems you can either deliver 23.987 progressive or “29.976i” which is 59.9 interlaced (stupid naming but europe sometimes also calls 50i as 25i) , one would get the 59.9i by using 3:2 pulldown on the 23.976 progressive source. either you do that or the distributor just like in europe

  4. over the air its running at 59.9i

  5. Tvs will be able to detect 3:2 pulldown and reconstruct it back to 23.987 progressive.

Option2)

  1. you shoot in 29.976 progressive

  2. you work in 29.976p

  3. you export this either as 29.976p or 59.9interlaced, getting the interlaced one with the same method as in europe so 29.976psf , either you or distributor does this conversion - again.

  4. over the air it will all be 59.9 as always

  5. Tvs will be able to reconstruct it back to 29.9 progressive.

Does that sound right?

I mean its not possible to switch FPS during a broadcast so each channel will have to have a fixed framerate so with 3:2 pulldown (some tvs do have a special pulldown removal option which i guess recreates the true 23.9 fps if they detect pulldown?)

In this case considering the whole chain not just “i was able to deliver 23.987p no problem” that just means the conversion happens somewhere else.

Or maybe I am missing something and some channels are actually broadcasting at 23.9 progressive? That would make them showing actual 29.9 documentary material kinda hard though so i doubt that.

Have 720 60p channels dissapeared now? I remeber some doing that? also what happens with streaming broadcast systems is stuff just re-encoded to progressive from the broadcast interlaced signal?

just wondering as there is always discussion about converting 23.9 to 29.9 but it seems like the actual thing thats happening is 23.9p->59.9i ?

41

also looking at it it seems that gv alchemyst can be had software only, couldnt find a price but its integrated into telestream something enterprise for like $6K .

42

Where it gets a bit more complicated is if you have projects that go to both broadcast and theatrical, which is not uncommon in documentaries. We have one of those at the moment - a mix of everything in the source. It was finished in 23.976, and from there goes into a 24fps DCP and a 29.97/59.98i broadcast deliverable.

So the other variable you have to add your list - if a whole program was shot and finished in 29.97p for broadcast as primary, but then needs a 24fps DCP, you have that conversion to do.

In that documentary we had a few low altitude/high speed drone shots where the mismatch in frame rate produced visible jumps as the frames ever so slightly shifted due to conversion. Ended up having to treat these separately with an ML based tool for some frame blending.

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