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720p25 over 60p (Varicam)

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  • Guest's Avatar
    Guest replied
    Further to what Rick is saying... The issues with most NLEs for PAL users is the disparity between the 59.94/60Hz operating frequency of the deck and the 50Hz based framerates the applications are working with in PAL framerates.

    As for the constant 60fps - it is indeed recording 60 images per second to a tape, but as I said before, only a certain number are unique - only the flagged frames. In 25fps, the camera samples the sensor 25 times a second and records that frame to tape. Essentially you get frame 1 recorded for 2 frames, frame 2 recorded for the next three frames, frame 3 recorded for 2 frames, etc... The first frame with each unique image is 'flagged'. To rebuild the recorded framerate, only the flagged images are captured.

    The big bonus of Edius for me here is that it can capture the PAL framerates from the 59.94Hz deck over Firewire directly. Something that Avid and FCP are unable to do.

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  • Guest's Avatar
    Guest replied
    Originally posted by GrassValley_BH View Post
    True, it's insanely difficult to run magnetic tape as a non-constant speed. Too much mechanics involved to get it reliable and affordable.

    Ahh, okay, I figured out my confusion...

    The variable frame rate function is supposed to allow for blur/slow effects, but even the operating instructions don't really tell you what to do with it after it's on tape. Weird.
    Some clarification here. The Varicam does indeed record at a constant 60fps. If the frame rate is set to 25fps for example it simply flags the active frames. This flag is carried in the vertical interval data. The reason for this system, is as suggested, it is very difficult to vary the speed of tape in a helical scan recording system. With the advent of solid state recording that Panasonic introduced in the AG-HVX200 it is now possible of course to only record the active (native) frames and this would be called 25pn for example.

    Originally with the Varicam you used to use a device called a Frame Rate Converter. This box contained a hard drive with HD-SDI I/O. It would recognize the active "flagged" frames in the incoming signal and buffer them through the hard drive and then play them out at the correct frame rate.
    More recently NLE's such as Avid, FCP and Edius have incorporated this flagged frame recognition and perform the extraction automatically. Thus when I tested a 25fps Varicam ingest on a 25 Frame timeline I am getting realtime playback. If I had recorded at 50fps and I placed that on a 25 frame timeline I would have very smooth half speed. Also the newer DVCPRO HD decks such as the AJ-HD1700 and AJ-HD1400 have the ability to decode "on-speed" frame rates such as 30fps, 25fps and 24fps.

    The issue that Dylan is facing is that the NLE's will not accept a firewire input at 60Hz, they only accept it at 59.94, this is a .001 frequency difference and should be negligible. The other alternative is to ingest via HD-SDI via a Black Magic or AJA Kona card etc. These boards also support the variable frame rate function.

    I hope that this helps clear things up a little.

    Rick Haywood
    Manager Broadcast & Display Systems
    Panasonic New Zealand Ltd.

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  • Guest's Avatar
    Guest replied
    Well we're buying a full copy of Edius 4.5 Broadcast today, so we're commited I guess.

    Fun times ahead.

    Edited:
    And here it is... Now I have a fancy box and all. Choice.
    Last edited by Sycophant; 10-18-2007, 12:35 AM.

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  • SRsupport
    replied
    Plug and Pray? :)

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  • GrassValley_BH
    replied
    True, it's insanely difficult to run magnetic tape as a non-constant speed. Too much mechanics involved to get it reliable and affordable.

    Ahh, okay, I figured out my confusion...

    The variable frame rate function is supposed to allow for blur/slow effects, but even the operating instructions don't really tell you what to do with it after it's on tape. Weird.

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  • Guest's Avatar
    Guest replied
    Originally posted by SRsupport View Post
    When you have captured the file in that project select a clip in the bin press alt+enter go to video info and tell me what the framerate is .
    In a 50p over 60p project, when I capture footage shot 25p over 60 with the 'Constant Rate' capture profile I get a clip in the bin that is 50fps, but that plays at doubletime - which is what I'd expect.

    I can change the framerate in the properties to 50fps, and it plays at the correct rate, but I'm not happy with the way to refactors the timing in that mode. It seems to create interpolated frames to fill the gaps, which provide an unusual appearance that I don't really like.

    At present if I capture into 25p over 60p project, then import the resulting 25p footage into Avid, Avid doubles up the frames to produce 50fps material.

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  • Guest's Avatar
    Guest replied
    Well, yes. Sort of. I'm not sure about the rationale, but basically I believe that it's hugely difficult to run tape at a non-constant speed.

    The Varicam records 60 frames, and of those 60 frames anywhere from 1-60 can be 'active'. Other frames are duplicates of those active frames. In capturing the footage the NLE simply takes the frames that are tagged as active.

    It is possible, somehow, to shoot a constantly higher framerate (say 50fps for PAL rates, and 60 for NTSC rates) then you can pull a different (evenly divisible) rate from it.

    The problem would be, if the camera always recorded 60fps, that it would be impossible to get any framerate that wasn't evenly divisible by 60 as smooth motion. So getting 30 or 15 is easy, just take every 2nd, or 4th frame. But to get 25 out of that wouldn't work.

    Sony has just launched their XDCAM EX camera, which also offers variable rate shooting. Not sure what it does, but I believe it's a similar thing.

    The RED camera is different however, as it's basically just shooting an image sequence - it's like film.

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  • GrassValley_BH
    replied
    Hmm, seems my understanding is flawed then.

    So if only 25 out of the 60 images are unique, isn't it just a waste of space?

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  • Guest's Avatar
    Guest replied
    Not quite. It only records the target framerate, but spreads it over 60 frames.

    So if shooting 25fps, only 25 of the 60 frames have a unique images. ie, you can get more out of it than you recorded in.

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  • GrassValley_BH
    replied
    Varicam essentially runs the camera "overcranked" all the time, so the are more samples than the target shooting rate. The extra samples can then be used for slo-mo, or simply the change the playback rate.

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  • SRsupport
    replied
    Originally posted by Sycophant View Post
    Neither myself, nor Ricksta (I don't think) are using NTSC-rate profiles.
    I've also tried a 50p over 60p project setting (as 720p50 is what I will be editing with in Avid) - but, predictably, this works but gives me double-speed footage. Which, while amusing, isn't a lot of help for me :)
    When you have captured the file in that project select a clip in the bin press alt+enter go to video info and tell me what the framerate is .

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  • Guest's Avatar
    Guest replied
    Neither myself, nor Ricksta (I don't think) are using NTSC-rate profiles.

    The Preset setting I've been testing with is:
    Generic OHCI HD 50Hz 960x720 25p over 60p

    Indeed, I've just tried what Rick mentioned, and with the deck in 59.94Hz operating frequency, I can capture with all three 720p 59/60 input settings. This is technically wrong however, as the tape has been recorded at 60Hz. But like I said before, until Rick hears from the big geeks at Panasonic about this, I don't know what the real outcome of that difference in frequency is.

    I've also tried a 50p over 60p project setting (as 720p50 is what I will be editing with in Avid) - but, predictably, this works but gives me double-speed footage. Which, while amusing, isn't a lot of help for me :)

    A large part of the problem I'm facing here is to do with the Varicam format. It will record any framerate from 1-60fps. It has to operate and a system-frequency of 59.94Hz or 60Hz. That is what Rick and I are referring to. The limitation I face is that the Varicam format is not widely supported for PAL-based rates (25/50) as it requires communication with a deck operating in an NTSC-based system frequency (either 60Hz or 59.94Hz). This difference (between project/timeline framerates, and deck operating frequencies) is enough to ensure that IEEE1394/Firewire/OHCI capture is not possible in these modes in Final Cut Pro, Avid (any version) or any other NLE I have found.

    We realise that the framerate and frequency we're working in has to be 50-based, and we're not making any mistakes in that respect.

    So far Edius is the only NLE on the market, that I have been able to find, that supports Firewire capture from 60Hz DVCPro HD material in a 50Hz based framerate.
    Last edited by Sycophant; 10-16-2007, 02:53 AM. Reason: More detail

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  • SRsupport
    replied
    But the other problem is that you are using an ntsc profile to capture pal recorded footage.

    50 hz 960x720 over 60P yields a frame rate of 25 progressive

    60 hz 960x720 59.94p yields a frame rate of 59.94 progressive which is far from your original footage . Mostly used for countries using natively ntsc




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  • Guest's Avatar
    Guest replied
    Sorry, my mistake someone interrupted me in the middle of the post and I mistakenly typed 60Hz instead of 60p.

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  • SRsupport
    replied
    50HZ 960X720 25p OVER 60HZ there is no such setting in EDIUS.

    There is a 50 hz 960x720 over 60P

    You guys seem to confuse that alot

    It makes me think that maybe the source format is also confused .

    hertz and progressive are different things
    Last edited by SRsupport; 10-16-2007, 12:21 AM.

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