GH1-1080/24p It Doesn't Drop Frames; It Reapeat Some Frame...

Polanski

Polanski

Well-known member
After playing around a while with DavidNJ's footage.

http://www.dvxuser.com/V6/showthread.php?t=170839

I discovered that playing the 1080/24p frame by frame, it repeats a frame at cartain intervals of frames. This could be the reason why things moving fast appears to stop and continue.
Is this normal in 24p. I've noticed this in D90 videos too, but I thought it was my computer not being able to play smoothly. It's not, because this does not happen with 720/30p...
Any comment will be appreciated...
Thanks
 
You need to remove pulldown first before playing the footage frame by frame.

That's what pulldown does... it repeats frames (well...fields actually) to make 24 frames fit into 30.
 
Remove pulldown? You mean that every time you shoot something at 24p you have to remove pulldown... If you do that you'll be converting your footage to 30p. Is that the way it should be done... Why do I have to remove pulldown if I want my video to be 24p?
Why 24p doesn't play smoothly?
 
I haven't been able to remove pulldown correctly with a couple of GH1 samples so far. I've tried doing it with After Effects CS4 native "interpret footage" option and with RE:Fieldskit with no luck. The closest I can get to perfect removal shows interlaced frames from time to time, and I've tried several different frame order options.

Can anyone post a way to remove pulldown with the GH1 footage with no repeated frames and no interlacing artifacts?
 
I know that SEVERAL people have posted ways to remove pulldown. I haven't seen anything specific to repeated frames, but I know that PULLDOWN ITSELF is related to removing repeated frames. Just do a search, this info is in seemingly 1 of every 2 posts.
 
I just need to point out that this thread title is misleading in that it confuses pulldown with repeated frames.

Here's how to remove pulldown.

http://www.dvxuser.com/V6/showthread.php?t=170717

And I said this elsewhere when it comes to removing pulldown.
I have found that to properly reduce the pulldown I've only been successful from importing the original "Private" file into final cut with prores, and then removing pulldown with either Compressor or JES Deinterlacer. I've actually found that JES looks a little better than compressor.

Removing pulldown from just the MTS clip with no metadata from the original folder has been damn near impossible, but with the original folders intact it works as it should. You wouldn't import P2 by stripping the folders apart, and you need to take the same approach to AVC-HD. You remove that original file from the folder structure and you lose all the metadata for it.
Click to expand...
 
Isaac_Brody said:
I just need to point out that this thread title is misleading in that it confuses pulldown with repeated frames.
Click to expand...

For whatever reason, FCP sometimes (all the time?) makes the 4th and 5th frames in a series of telecined 24p frames appear tojust be repeated. I'm sure there's a reason for this, but I've never bothered to look as I don't spend much time editing 24fps footage that's telecined to 60i.

Polanski, what are you using to watch the footage?
 
I always watch any footage in Windows Media Player first, then in Edius timeline...
BTW, Windows Media Player in Windows 7 plays almost anything in real time.
 
What I can't comprehend is why doing a pulldown to a footage that was shot at 24p...
I've always thought the a pulldown is applied to footage other than 24p.
 
Polanski said:
What I can't comprehend is why doing a pulldown to a footage that was shot at 24p...
I've always thought the a pulldown is applied to footage other than 24p.
Click to expand...


As with MANY, MANY other cameras, this camera shoots 24p in a 60i "wrapper", thus you need to do a reverse telecine process on it. This has been discussed ad nauseam.
 
Polanski said:
What I can't comprehend is why doing a pulldown to a footage that was shot at 24p...
I've always thought the a pulldown is applied to footage other than 24p.
Click to expand...
Think of a cam like the DVX's 24p....same thing. The HV20's 24p.....same thing. The footage is progressive but with puldown added. Just find the right tool (NLE) to remove it and you have a fully progressive shot.
 
Now I get it... Pardon my ignorance. I didn't know that cameras shooting 24p work in such a weird way...

Thanks.
 
Actually...lately...not all of them do any more. For example...the upcoming HV40 replacing the HV20/30 will be shooting "native" 24p...which is a great thing. But traditionally... cams like the ones I mentioned above all shot 24p with pulldown added.
 
"Pulldown" refers specifically to the technique used to convert 24p footage to 60i. It is used by the telecine process in order to turn film (which is always shot at 24 fps for "normal" motion) into an NTSC video signal, which is 60i. Please read the relevant Wikipedia article for an explanation on why it's called "pulldown" in the first place.

You're confusing pulldown with interlacing. Interlacing merely refers to an encoding scheme used for the efficient transmission of a video signal. Deinterlacing refers to any method of constructing a progressive signal from an interlaced signal. That's probably why you assumed that "removing pulldown" (AKA deinterlacing, in your mind) meant that you would be getting a 30p signal from 60i. While some deinterlacing methods weave the fields together (getting you 30p), the reverse telecine process actually reconstructs the original 24p signal through removing the pulldown scheme.

The vast majority of consumer and prosumer 24p camcorders use pulldown because the manufacturers want the video to have backwards compatibility with NTSC video systems, such as older TVs. There's nothing weird or unusual about it. There should be no more confusion now.
 
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Ydgmdlu, thanks for letting this so clear. I was confused in the first place because that was exactly how I knew about telecine, interlacing, and pulldown.
Then in fact a camera shooting at 24p IS 24P and DOES NOT need anything else except removing artifacts of bad desinterlacing while converting 60i to 24p.
Am I right?
 
No. You have to find out how any given camcorder encodes the 24p signal. There are four methods in which it's done.

The first method is to encode 24p as 24p. Canon prosumer camcorders, such as the XH-A1 and the XL-H1, do this in their fake 24p mode. Since this is already 24p, nothing more needs to be done about it.

The second method is to encode 24p as 24p with a pulldown flag. The pulldown flag tells the playback device to perform a on-the-fly, real-time telecine on the video stream. Pulldown flags are a feature built into MPEG-2, MPEG-4, and AVC. They are most commonly used on DVDs. You can get the original 24p signal simply by ignoring the pulldown flag. However, I am not sure if any camcorders use this method. Some HDV camcorders might, but I'm pretty sure that the DVX100 doesn't, since the DV codec doesn't have this feature, as far as I know.

The third method is to encode 24p as 60i with the pulldown information in metadata. A decoder or NLE can use that information to perform an inverse telecine to reconstruct the 24p signal. This is obviously an inferior method, as per-frame bandwidth is lower than that of native 24p.

The fourth method, which is what the GH1 uses, is to encode 24p as 60i. There's no easy way of doing inverse telecine because the pulldown pattern (i.e. "cadence") is unknown and could change at every cut.

There is no such thing as "bad deinterlacing," other than simply weaving the fields together. There are many different deinterlacing methods, each with strengths and weaknesses, but there will never be artifacts to remove if a deinterlacing algorithm has done its job. The only artifacts there could be are ghosting and duplicated frames. Ghosting can't be removed, at least not easily, and duplicate frames are not an intra-frame problem.

There could be artifacts if inverse telecine (IVTC) is not done properly. This happens when the wrong cadence/pattern is used in the IVTC process. The only way to remove the artifacts would be to break up the image into fields and perform deinterlacing all over again using a different method. There are never any artifacts if IVTC is done properly. What's frustrating about GH1 24p footage is trying to find a reliable IVTC method.
 
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According to all this arcanum, in your experience, which could be the best method to have real 24p in the end? Shooting 720/30p and converting them to 24p using something like Magic Bullet Frame Plus? The first time I heard about the GH1 with a 1080/24p, I was really excited... Converting footage 29p, 60i etc... to 24p using any of the famous plugins is time consuming.
 
Please read the GH1 workflow forum. There's plenty of discussion there about how to get what you want. This thread is extraneous.
 
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