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Old November 29th, 2009, 10:01 PM   #1
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Workflow, Frame Rates and Scan Type

Iím new to all this and need to decide before I start shooting too much footage which frame rate and scan type I should be using.

Iím shooting documentary style stuff with the hope that some of it might one day be aired on TV. Iím in PAL land, so do I go with 25 fps or 50 fps and progressive or interlaced. The resolution is 1920 x 1080 and I was thinking of shooting in 50P. Will there be any problems in converting to 25P as I not sure if TV can be broadcast at 50 fps. One thing that puts me off 50P is that I canít see an option in Vegas to render at 50P for DVD's. Or would you never render a DVD at 50P, in which case why shoot in 50P in the first place.
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Old November 30th, 2009, 01:07 AM   #2
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I'm sure you'll get advice from people more experienced than me, but I'd recommend shooting at 50i (interlaced).

That way you've got interlaced video, ready for tv, and it's more easily converted to other formats than progressive footage. With Vegas you can render it out to just about anything... You can turn interlaced video into progressive (or interpolated) video, but you can't turn progressive into interlaced.
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Old November 30th, 2009, 05:52 AM   #3
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Now there are not many cameras out there which can do 1920x1080 at 50p. So you should check your camera if it's even able to capture that.

Most likelly it can only do 1280x720 at 50p.

In theory there is no problem with shooting 50p and working the footage in a 25p edit project. It will simply throw away every other frame. In practice, Ive noticed that the 50p footage can look slightly more stroby when edited at 25p, than it would be if you had shot it at 25p. As a rule I would only record 50p if I was intending to do slowmotion at some points. Or simply edit it at 50p or even 50i if thats the delivery format required.
I am not aware of any problems with converting 50p footage into 50i. It seems to be an inherent issue in NTSC land where pullups are required to make 24p into 60i.

As for DVD's they are only SD resolution and dont have any 50p option. For that you need bluray.
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Old November 30th, 2009, 06:26 AM   #4
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Yep the camera is not native 50P 1920 x 1080, but I use an intermediate AVI that becomes 50P after conversion.

Iím not sure whatís going on here at all but I will try and explain what I did to get the 50P. The camera I use captures at 1920 x 1080 50i or progressive segmented frame, where an interlaced frame is made up of two fields that both represent the same instant in time. If I load the AVCHD files into Veags both 50i and 50 psf are seen as 1920 x 1080 25 fps interlaced when I view the clips properties. Iím not sure why that is as I thought it would show 50i, but other NLEís I have also show the footage to be 25i. If I convert to a CineForm AVI intermediate file I have the option of setting the frame rate to 25 fps or original frame rate. If I choise to keep the original frame rate, after conversion the 50i footage becomes 50 fps interlaced and the psf footage becomes 50 fps progressive. Both are 1920 x 1080 and Iím not using any deinterlacing.

I can understand why broadcasters require interlaced footage as everyone used to watch with a CRT TV, but surely this has to change soon as most the equipment used to view TV is now of a progressive nature. If I supply interlaced then the viewers TV will convert to progressive anyway, so I thought by supplying in progressive there would be one less conversion taking place.

As you can see I need some help on this one as Iím not sure whatís going on or the best way to start shooting with my camera.
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Old November 30th, 2009, 08:23 AM   #5
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hm.. It sounds like there is a lot of conversion going on in your workflow already, and possibly a lot of resolution loss aswell. So my suggestion would be.. keep it native untill told otherwise by the customer. You dont need to convert pre edit. You can do that after the fact.
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Old December 1st, 2009, 04:04 AM   #6
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Rog, Do NOT use Psf if you are shooting interlaced. Either you will be burning in the interlacing to progressive frames, which is sure to cause interlacing artifacting later on, or you are 'de interlacing' your footage which means you are losing half of your vertical resolution (which means when you downres to SD you will get increased aliasing.)

Shoot for your delivery format, 1080p50 is not currently a broadcast standard anyway and won't be for a long time. 1080i50 (really 1080i25) or 720p50 can be converted easily 25i (the only way Standard Definition programs are broadcast, nothing is EVER broadcast as 25p)

If you are shooting 720p50 and editing it down to 25P then it will be extra strobe like because your shutter angle is effectively double your frame rate, with every other frame thrown away. You are much better off converting it to Standard Def with interlaced frames (if the conversion is done correctly it should take a field from each individual frame) and get a more or less identical picture to what you would have got had you shot on an interlaced format.
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Old December 1st, 2009, 07:35 PM   #7
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Thanks for the replys Craig and others.

Ok, I wonít use the devils spawn of scan types, Psf.

I have noticed some artifacting taking place when I render any Psf footage to progressive, but its very small. The 50i footage doesnít have any artifacting but maybe doesnít look quite as good quality.

So, the next big question and probably the most stupid question ever. Why if its 50i is it really 25i. Why canít they just say 25i in the first place. My camera says 50i on its body and in the manual, but Vegas tells me its 25i. Is someone lying. And why if I convert to a CineForm AVI and keep the original frame rate during conversion does Vegas then tell me that it is 50i.

One last question and I know this one has been done to death. Is it best to edit AVCHD footage natively in Vegas, or is it best to use an intermediate CineForm AVI file. I know everyone has there way to do it and thatís different for everyone, but there must be some technical reason as to which is best. Or at this point are we just talking subjectively and go with what feels right for the individual. My PC will edit AVCHD natively without any problems so I donít need to use an AVI intermediate to be able to edit. I just heard a lot of people say that the 4:2:2 colour space of a CineForm AVI holds up much better when having FX applied and I do like to play around a lot with FX in post.
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Old December 1st, 2009, 09:10 PM   #8
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What you heard about an intermediate codec holding up better to colour correction/FX is absolutely correct.

The difference between 50i and 25i is what they are referring to, and because marketing people like to use bigger numbers whenever possible they opt for 50i

50i is 50 interlaced fields per second. Each field is one half of a frame, so it's effectively 25 frames per second. Except, because it's interlaced, it's not really Frames at all, but fields - so that's kinda the argument behind 50i the right descriptor.

25i is talking about 25 Frame per second playback, made up of interlaced fields. In other words the exactly the same thing that people mean when they say 50i.

The thing people get confused about is they think that 50i means they are recording at 50 frames per second - this is not true, it's 50 half frames per seconds (fields). Which means you can never get 50 frame per second playback out of 50i footage, except via interpolation, or potentially downressing.

Psf stands for Progressive segmented frames. Basically it uses interlaced signals to transport progressive frames. So 50Psf IS actually 50 frames per second, and 25Psf is actually 25 frames per second - the information is just being transported of an inherently interlaced signal and then recognized so that it gets displayed correctly (i.e progressively) on the end display.

It's a good format if you shoot Psf, or progressive, and need to deliver as such.
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