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Is this a legitimate way to convert a 23.98p master to 50i (PAL)?

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Mel Matsuoka
Is this a legitimate way to convert a 23.98p master to 50i (PAL)?
on Aug 23, 2016 at 9:24:31 pm
Last Edited By Mel Matsuoka on Aug 23, 2016 at 9:25:55 pm

I have a 1080p23.98 ProRes master for which my client has requested that I make deliverables for a broadcast in a PAL region.

Normally, when we deliver for North American broadcast, we convert 23.98p masters to 59.94i, using 2:3 pulldown (via Compressor). As expected, this looks good on TV, and our spots don't exhibit any stuttering on the air.

I know there a lot of discussions on message boards and knowledge base documents on this topic (like this tech note from Autodesk), and many of the answers involve either running the conversion through something like a Teranex, or conforming the playback of the master to 25 and adjusting the speed/pitch of the audio track accordingly.

But as an experiment, I simply converted my 23.98p master to 50i via Compressor, using similar settings that I normally use for generating 59.94i deliverables with interlaced pulldown:

This generates an interlaced 50i deliverable, and when I bring this file into Premiere, configure my sequence and Decklink playback options to play this file out as a 1080i50 signal to my broadcast display, it looks great, with no apparent visual artifacting from the frame rate conversion.

When I inspect the file in Quicktime Player, the field/frame cadence that Compressor added does not appear to be a regular cadence (unless the complete cadence is being stretched out over many seconds or something...I stopped counting after 20 frames or so), but as mentioned, when the file is played out through a (what I believe to be) a properly configured 1080i50 playback path to a broadcast monitor, it looks just like our 59.94i masters...that is to say, it looks great!

Is this a valid workflow for conversions like this? I'm wondering why this simple method is never mentioned in any of the discussions of questions like this, so a part of me is questioning if this is a bad idea?

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Matt Quinn
Re: Is this a legitimate way to convert a 23.98p master to 50i (PAL)?
on Sep 10, 2016 at 10:57:28 pm

It's not really an answer to your question, but 'traditionally' film (shot at 24 FPS) was/is run at 25FPS and the speed/pitch difference often ignored. Autodesk hint at this in their notes. This is as acceptable to 'PAL' viewers as the 3:2 'look' is to Americans.

I'm not familiar with your software - but what causes you to believe it ISN'T just producing a frame-by-frame transfer speeded up by 4%? Or even that the software doesn't interpolate the 'missing' frames for you? "the field/frame cadence" - Not sure what you mean by this. A frame is split into two fields... Simple as. Are you expecting some sort of 'pulldown' artefact? There is no reason for there to be one.

However, this all may be academic. If you're delivering for BROADCAST to the UK or many other 'PAL' countries (a misnomer I know) you should probably familiarise yourself with the AS-11 DPP requirements... And for a start that's an MXF OP1a using the AVC100 codec!

If I were you I'd farm this out. If you supply your client with what you have it will only have to go out to a finishing house to be 'wrapped' anyway, which will involve them transcoding it. I suspect they might do a better job if they got the 'unmolested' 23.98p file.

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