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Re-interlacing footage at the broadcasters request: normal or not?
Hi all:
A couple of days ago I asked about deinterlacing filters, and then it turned out that what I needed was the opposite, i.e., a filter to re-interlace progressive footage. I know how to do it (FieldsKit), but that’s not what I’m asking about here.
Let me explain: we deliver an hour-long show shot with the HVX-200, and up to now we had been shooting, editing and delivering in progressive (DVCPRO) for a variety of reasons. Well, a couple of days ago I was told that the technical lead of the TV channel was objecting to the image quality of the show, saying that there was trouble with the fields or something. I went with our producer the next day to the TV channel to talk to him, and it turns out that the problem wasn’t the field order, but the absense of fields. He showed us our show in an Avid, advanced field by field and, as it happens when you do that in progressive footage, there was only movement in one of the two fields. “That’s what’s wrong”, he basically said. “There isn’t enough information in the video signal, and the movements look jerky”.
I tried explaining to him that we were shooting in progressive, but he didn’t buy it: “video signal is supposed to have two fields, and there should be information in both of them”. He stopped short of claiming that it was a showstopper, but it was clear that there was something technically wrong with it; at one point, he told me that this (delivering progressive material for interlaced broadcast) was as if you were trying to sell somebody “a car with three wheels”. (Incidentally. neither me, nor our producer, not the editor actually working on the project saw any jerkiness in the progressive footage).
Anyway: I know that we’re supposed to deliver things in whatever the channel asks us to, I’m not complaining about that, and we’ve already arranged things to start shooting in interlaced and using FieldsKit to re-interlace the progressive material already shot, but what I’m asking here is: is this a “normal” request? Have you ever found a broadcaster refusing to air progressive material because they are broadcasting in interlaced? Do you think that the technical lead in that channel was being… erm, overlay fastidious, or that we’re the ones in the wrong?
(This is all in PAL-land, using SD, not HD, by the way).
Paulo.
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65 Replies
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Paulo
I wouldn’t say there’s a ‘normal’ for this situation. People often shoot in progressive for the film ‘look’ (as may well be the case with you), and that’s much more often the case than people shooting progressive for technical reasons.
Is he incorrect? Well, in a way yes, if he described the final edit as wrong or jerky, or lacking video information. Any movie they broadcast is probably progressive in nature (barring pull down, which is just a fudge to get the frame rates to tally, which is less common in PAL-land), so that might be a way of approaching the subject. Certainly, it’s the choice of frame rate for high end documentary work as well these days – and it does give a ‘jerkier’ look to fast moving shots that many people love for the film look it apes. Suggest he looks at film derived material shown on the channel, if that is possible.
However, it’s not as simple as that (what is?) If the programme you delivered is part of a strand or may be integrated into other shows, having the different look could be an issue. If shooting progressive is a ‘look’ choice for you, it’s also a ‘look’ choice for the channel. He needs to set a spec for material based on similar productions – in my experience that’s not uncommon, and varies from format to format (where for example HDV footage may be acceptable for news/reality/doco but not for drama etc.)
That said, he sounds like an ass to me.
Ben
Editec Broadcast Editing Ltd
EVS & FCP specialists for live broadcast.
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[Paulo Jan] “I tried explaining to him that we were shooting in progressive, but he didn’t buy it: “video signal is supposed to have two fields, and there should be information in both of them”.”
Sorry, but who is this guy? Does he not know that progressive footage means that BOTH fields contain information…the SAME information. Progressive doesn’t toss out a field at all. And it will look a little “jerky” compared to interlaced. That’s the point. FILM LOOK as opposed to very hyper smooth TV SOAP OPERA look. Where has this guy buried his head?
Progressive doesn’t have field dominance, AFAIK.
How the heck do you interlace progressive footage? Are you supposed to make up field information or something?
\Shane
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First of all, thanks to both you guys for confirming that I’m not crazy. Now, I think this guy did know what “progressive” means, he just didn’t want it, for whatever reason. And yes, I thought about asking him: “so, when you guys show ‘Saving private Ryan’ in your channel, are you going to ask Spielberg to reshoot the battle sequence in DV just so that the source material comes interlaced?”. But I preferred to be diplomatic…
To be fair, we aren’t shooting progressive for the “film look”, but for a variety of technical reasons, and our show isn’t a high-end doc or anything, but an hour long magazine (don’t know if it’s how it’s called in English: sort of current-affairs, cultural events, etc. features), so arguably we should be shooting in interlaced, but I don’t really think it’s such a big deal: after all, our show isn’t going to be integrated anywhere else as Ben suggested (it’s a stand-alone), so it’s not as if there’s going to be a huge difference in looks (what I mean is: there isn’t going to be the kind of abrupt change Ben is talking about. I didn’t mean that there wasn’t difference at all between the progressive and the interlaced look).
Lastly: how do you reinterlace progressive footage? The solution I found was FieldsKit, which has that option. From the quick tests I did, it seemed to do a reasonable job, but of course, I’m afraid there *might* be some quality loss…
Paulo.
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I dissagree with the comments made thus far because they are not correct. The guy at the station is 100% right although no one has stated the correct reason why.
24 FPS progressive should only be used if you are going to out put a transfer back to film. Film does not have interlaced fields and will look OK with fast movement. On the other hand 24 FPS progressive will look like crap on a NTSC or PAL system because there is indeed not enough information for each field. Say you had 640 X 480 progressive scan at 30 FPS. The fields will only be 320 X 240 and they will be repeated twice for each field (NTSC 60 field). If you had 640 X 480 progressive at 60 FPS it would look much better because there is more data. Each frame would still have 320 X 240 of data for each field (odd and even) but the data would be different not repeated. It would look smoother. Use NTSC or PAL if you are going to broadcast over the airwaves.
There is a time and place for 24FPS and progressive scan. If you were to make an actual film that would play in theatres you would want to record at 24FPS. If you used NTSC or PAL mode to record your film you would need a reverse telecine process to transfer to film. It would be retarted to record in NTSC mode for a film release. It would also be retarted for anyone to use 24FPS progressive if the final out put is for broadcast. Movie theater films shot in 24 FPS will look OK on TV but that is because they are using a telecine type system to make it look good.
I would have expected better answers from the FCP crowd. Any way there is the correct answer. You will not get a film look if it is broadcasted in NTSC or PAL because the progressive frame size of 640 X 480 is broken down in a very crappy way. You would get a film look if your final out put was to film.
I am not sure about the siz of resolution for yuor camera but it does not matter. The theory is the same.
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He doesn’t say he’s shooting 24p, he says progressive. In PAL land (where I assume you are not) that usually means 25p as opposed to 50i. Since when does saying that you shot progressive imply that you have shot at 24p?
Clearly if he shot in 24p, that would be a different matter, and would have got a different answer. Chill out.
Ben
Editec Broadcast Editing Ltd
EVS & FCP specialists for live broadcast.
OB Server 1 HD – Mobile FCP editing done right.
https://www.editecuk.com/OBServer2.html -
Yep, we’re shooting 25fps, using the HVX-200’s “576/25p” mode. When watching the footage in Avid or After Effects field by field, I don’t see any resolution loss, just movement advancing every two fields.
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There is no resolution loss at 25p. If your project stands alone, there is no technical reason to reject a 25p master – bodging the fields with fieldkit cannot restore motion that is not there, it’s a nonsense. And I take your point about motion not looking ‘jerky’ – it’s just a different look, as I said.
Ben
Editec Broadcast Editing Ltd
EVS & FCP specialists for live broadcast.
OB Server 1 HD – Mobile FCP editing done right.
https://www.editecuk.com/OBServer2.html -
24 fps or 25 fps makes no difference. I admit one extra frame would have a tad bit more data but in the end the full frame size of 640 X 480 is reduced to repeated odd and even fields of 320 X 240. You will not get the film look or quality you want. If you have a DVD burner and software that burns progressive and a DVD player that plays true progressive hooked up to a high end projector then it will look good (full 640 X 480). It should play back OK as an uncompressed AVI or quick time file on the PC or Mac.
640 X 480 is just a reference resolution I used for this thread.
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Paulo Jan,
I admit you may have some very good transfering software as far a resolution is concerned (it may interpolate) but in the end the data is not there to have smooth motion for every frame/field of NTSC. You can use it but it would be wise to opt for NTSC or PAL depending on your location.
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hi arc, it seems you are saying that shooting & editing in 24P progressive will not look very good if in the end the program must be delivered interlaced for broadcast. (e.g. 1080i)Do I have that right? What then is the best way to achieve the filmlook I see all the time on different cable shows? Is this done inside FCP or with an outboard converter?
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