BUG? 720p AVCHD = 30 frames only

J Davis

J Davis

Veteran
A week ago I was shooting 720p60 AVCHD using log&transfer in FCP and seeing a prores file with 60 frames.

Now when I bring it through I get 60 frames but they are doubled up and there is only 30 real frames in there.

I don't know if I changed something in the camera or in FCP

Has anyone else experienced this?
 
PappasArts said:
Did you shoot in 1/30th? Not that could be the case. However I have seen this..
Click to expand...
I don't think it has anything to do with shutter speed. I've seen it happen at 1/40th and tonight I did a test at 1/50th.
Can you elaborate on your situation where you have seen this?

EDIT:
I hope to post raw AVCHD footage soon
 
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Correct. ANY shutter speed slower than 1/60th will cause the GH1 (and every other camera in existence) to duplicate frames. It is not possible to have a shutter speed slower than the frame rate.
 
Oh boy I love forums. Thanks so much you guys. You are my newly adopted family.
For the hell of it I am shooting that same scene as above at 1/80 and 1/60 for ppl to download
J
 
It looks fine to me unless you put it in a 24fps timeline...which most will be doing, or put 60p footage shot at 1/60 and over in the same timeline with it. It will stick out like a sore thumb in that situation, too choppy next to 60p, and it won't really work at all in 24p timeline...lots of problems when final cut tries to drop frames out of it (think the pattern that sometime causes problems with motion when dropping in 60p but usually looks ok...time a zillion.)


EDIT:
Changed post completely after looking at footage and thinking about things.
 
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Once again Ben B and Barry Green, sincere thanks for your help.
John, the 1/50 untouched media straight from the card is available for download post 4

For all the pixel peepers out there who haven't got their camera yet
Here is some media at 1/60 and 1/80 also straight from the card available for download.
(same scene but handheld as I put my tripod way)

http://www.yousendit.com/transfer.php?action=batch_download&batch_id=Y1RyTkFrdGo4Q1FLSkE9PQ

This is me using YouSendIt to send it to myself so it should be good for 7 days or 100 downloads
 
Ben_B said:
It looks fine to me unless you put it in a 24fps timeline...which most will be doing, or put 60p footage shot at 1/60 and over in the same timeline with it. It will stick out like a sore thumb in that situation, too choppy next to 60p, and it won't really work at all in 24p timeline...lots of problems when final cut tries to drop frames out of it (think the pattern that sometime causes problems with motion when dropping in 60p but usually looks ok...time a zillion.)


EDIT:
Changed post completely after looking at footage and thinking about things.
Click to expand...


My main reason to shoot 720p60 is to slow down in post for the slow mo effect.
Otherwise I am 1080p24 all the way even if my delivery is 720
 
Try putting them in the same 60p timeline or same 24p timeline and looking at the difference ;)

That said here's a question for Barry: if you're shooting a project with GH1 that will be a 30p project, shooting most of your stuff 60p and dropping every other frame, is there any reason not to shoot 60p at a slower shutter if you'll be doing a lot of low light....I suppose you'd have to keep the editing timebase the same for the whole project (60 instead of 30) which means you'd be stuck shooting the whole thing slow shutter...sometimes might have excessive motion blur? Run into problems on export? Any thoughts?

Anyway that aside there is a purpose to the slow shutter on GH1...I've seen spectacular timelapses shot with it that were done by shooting slow shutter and speeding up the footage in post: you get a nice blurry effect that makes things seem like they're moving in normal time...just really fast (rather than choppyfloating around.) Particularly nice for driving footage, especially when there's no other cars around (to make things look like they're moving faster and maybe even add thrills to a low budget car chase.)

This footage is sped up a little fast but here's what I'm talking about:
http://vimeo.com/5569576

I will likely be doing some tests with this technique...I think sped up a little less, with less normal looking traffic, and lots of well shot, exteriors, with quick cuts, this might let you shoot a convincing low-for-high-speed chase.
 
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BenB: If you're completely sure you're gonna end up with 30p material the only reason to consider not to do it is excessive motion blur. We are all used to the 1/48 or 1/60 motion blur from watching movies and television all our lives. If the scene you are shooting has little motion in it, nobody will notice.
Another minor consideration (or major consideration depending on what you do) is that you will lose the chance to get beautiful slomo out of your footage (if you shoot 60p with a 1/60 shutter you have the option of deciding later if you want slomo, 30p o 24p and all will work out fine)
Since you seem willing to try new stuff, I would like to know what happens if you go with a shutter speed even lower than 1/30, does it record triple frames (resulting in a real framerate of 20fps?

J Davis: Thanks for the footage you uploaded!! I've been wating for raw 60p footage to try my 60p to 24p workflow in a PC!
 
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Yeah sounds about right to me. I'm not planning on shooting 30p stuff ever...my workflow will probably be 60p, reverse telecine'd to 24p, with 1080/24p stuff in there for low motion or times I know I don't need slow motion. I am planning on getting a few smaller cards and having a dedicated one for 1080p, and a dedicated one for 720p, to make my workflow easier in post...that or I'll just quickly slate my footage with my iPod touch or even my hand (one finger for 720, 2 for 1080...) I've found if you shoot a big mix it's a pain to seperate the footage and remove pulldown..not too hard, but kind of annoying.

Which reminds me, I think I'll drive down to costco tomorrow to pick up some cards!
 
dmoreno said:
Since you seem willing to try new stuff, I would like to know what happens if you go with a shutter speed even lower than 1/30, does it record triple frames (resulting in a real framerate of 20fps?
Thanks for the footage you uploaded!! I've been wating for raw 60p footage to try my 60p to 24p workflow in a PC!
Click to expand...


1/30 is the lowest and you're welcome about the footage.

I just ran out and shot some down and dirty midnight 1080p footage.
I will post that for everybody soon
 
Thanks for posting full private folders....when you get a few more up I'd pop over to the thread where everyone is waiting for their cameras to ship and link some stuff...I really wanted a chance to test out my post workflow. Make sure you say that's what it's for so it doesn't seem condescending lol.
 
J Davis see link in sig for frame rate tests and you can see 60fps with 1/50th shutter dropped into 24p timeline.

Basically if you have a shutter speed lower than your frame rate, you've created an impossibility for a physical shutter - an angle greater than 360º, so virtual shutters below the frame rate force the camera in to a hack to compensate.
 
Thanks Jack, you were beaten to the finish line by Barry and Ben but I appreciate the explanation. If I had stopped to think it through I would have realized as it is common sense but sometimes you can't see the forest for the trees if you know what I mean.

Ben_B said:
Thanks for posting full private folders....when you get a few more up I'd pop over to the thread where everyone is waiting for their cameras to ship and link some stuff...I really wanted a chance to test out my post workflow. Make sure you say that's what it's for so it doesn't seem condescending lol.
Click to expand...

Okay ... more native footage. Ben ... this one's for you !

http://www.dvxuser.com/V6/showthread.php?p=1690662
 
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Oooh boy I am excited, will post in other thread when I get a chance to transfer and play around!
 
J Davis said:
Can you elaborate on your situation where you have seen this?
Click to expand...

As I said in the second post, it's usually a result of shooting at 1/30th that I have done on other cameras ( slower than the needed 1/60th ) that this happens...
 
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