AC160 PREREC Mode

S

shellant

Member
Hello every one,
Firstly let me say that I am new to the forum but have been a fringe dweller for a long time.
Really appreciate all the input and comments from people here and think its fantastic that there are places like this to get more information than can be found in instruction manuals alone.

I studied comments and discussions here before taking the plunge and buying the AC160 and gotta tell you that I couldn't be happier with the choice.
I have been playing as much as possible to get myself up to speed with the camera and so far everything seems pretty straight forward.
I have been reading Barry's great book and getting very comfortable with where everything is.

I love the pre record feature and tried some pre recording today.
Everything was great and worked as described but I do have one question if any one is still with me. ( sorry , I get long winded)
It seems that Prerec Mode disables VFR.
I was shooting some tests today and switched to 1080/24p to be able to shoot at 60FPS but when I switched to prerec it seemed to reset the FPS to 24..and the only way I was able to go back to 60FPS was to switch off Prerec.
Am I doing something wrong or is this the way it is ?

Thank you to everyone in this forum who bothers to read and share. I hope to also contribute when I can.
Cheers
Tony
 
shellant said:
It seems that Prerec Mode disables VFR.
Click to expand...

That is as designed. see page 34 of the second manual.

But you should be able to set the camera to 60p once you've updated the firmware, if 60p is the frame rate you want to use with pre-record.
 
Thanks Mike for your response. I opened Vol 2. and went to page 34 and there it was. I must have been too excited to actually take that info in.
Being an old film guy I was trying to shoot something at 60 frames a second.Actually capture in camera. So would shooting 60p and then slowing it on the time line( in post) be what you suggested?
How is Cairns these days? I used to spend a lot of time in your neck of the woods shooting tourist commercials . I was based in Brisbane but now live in Florida..
How many people know what a paradise yopu live in????
Tony
 
shellant said:
Actually capture in camera. So would shooting 60p and then slowing it on the time line( in post) be what you suggested?
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In Premiere it's quite simple. I use 50p files all the time. If I drop them on a 25p timeline every second frame is skipped and it is as if I shot at 25p. If I set the clip to play at half speed the skipped frames are now used and I get smooth slow motion.

How is Cairns these days?
Click to expand...

Tourism took quite a hit last year because or the GFC, the strong Aussie dollar and the floods and cyclone, but things are looking much better this year.
 
Hi

While the discussion is about pre-rec, I have a simple question. On my TM900 I can enable pre-rec. I then start to record after a while. Then the pre-record has to manually be enabled again. And now the question: Is pre-rec allways enabled on the AC160 until you manually disable it, or will it be disabled as soon as you stop recording?

I find the TM900 "auto disable as soon you stop record" annoying, so I wonder if the AC160 is better.

Regards,

/Bo
 
Hi Bo,
pretty sure that you have to disable it but to be certain, if no one has gotten back by the morning , I will get to the office and test a few options and let you know.
Tony
 
Hi Mike.
Thanks again for your reply. I think I was hoping for the best of both worlds.
I did do a test where I shot at 60fps and it looked great and then slowed it down 50% on the time line. which seemed that , depending on what you were shooting looked pretty good as well. Then tried shooting something similar at 60p then slowing down to 50% and looked pretty good which is what I think you were suggesting? So if I really need the PREREC I will have to go about it that way But when I slowed it to 25% on the time line allot more strobe(ing).
Any Thoughts or am I just over thinking it.
Cheers
Tony
 
Hi Bo
Just did a quick test of PREREC Mode and once I Select PREREC MODE to ON it remains on until I go back to the Menu and select PREC OFF.
I switched the camera off While in PREREC MODE "ON" and waited 5 minutes before switching back on and PREREC MODE ON was still active.
I hope that is useful info
Tony
 
shellant said:
But when I slowed it to 25% on the time line allot more strobe(ing).
Any Thoughts or am I just over thinking it.
Click to expand...

When you slow down to 25% the frame rate is now 15fps so it will look a bit stuttery. Keep in mind that if you are using a 24p timeline, 15fps is not going to fit properly. I suggest you scale the time to 40%, then the frames will line up 1:1.

Also, if you're using any other NLE apart from Premiere, it may handle the files differently.

I suggest to do a test and shoot something like a ceiling fan so you have a constant speed subject. Try it in 60p and then at 24p with VFR set to 60fps. Drop both files on the same (24p) timeline and see how they look.
 
Hi shellant

Yes, that's exactly what I wanted to hear! The "auto disable" of Pre-Rec on the TM900 is pretty annoying, so Panasonic seems to have thought about this issue while designing tha more pro AC160. Nice to hear that it can be left runnig, even though it might consume some power when it's activated.

Regards,

/Bo
 
Hi Mike,
Thanks for sticking with me. I tried the ceiling fan today. Great idea , thanks.
Though I think I just need some schooling on terminology. In my mind if I shoot something at 30fps and slow it down 50% it becomes 60fps but your last post makes me think the terminology would be 50% of 30fps becomes 15fps???????? I know you talked about 40% , would that be 24fps??? Old Dog new tricks. I guess I think in film terms, where we assume that the playback speed is the constant, therefore the exposure speed is the reference??? Sorry . Tell me to rack off if you like but I have now thought myself in circles trying to understand.
I am using premiere cs5.5 and on the time line did what you suggested. I shot the ceiling fan at 60fps @ 24p and 60p placing all on a 24p timeline.
then tried different percentages 100,50 ,25 & 40 percent. All seemed fine but didn't really understand your comment
"15fps is not going to fit properly. I suggest you scale the time to 40%"
Could you point me in the right direction to read more about frame rate ( for knuckle heads) information.
sorry for my ignorance and thank you again
Tony
 
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shellant said:
Could you point me in the right direction to read more about frame rate
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I don't know of anything specific. I'm sure it's just my poor job of explaining things. I'll try to phase it a bit differently.

Forget playback frame rate for a minute. That only becomes relevant in the second part.

If I shoot something at 30pfs and slow it to 50% each frame will play for twice as long and therefore there will be half as many frames played in each second, hence 15fps. At 15fps we can start to see the individual frames as a series of still pictures and it starts to look a bit choppy.

Now, if we do the same thing, but this time start by shooting at 60fps and then slow playback to 30fps, the motion looks reasonably fluid (to most people).

Next, we introduce the other variable, playback rate.

Let's say we want our playback rate to be 30fps and therefore we're using a 30p timeline. It we drop our 60p footage onto this timeline at normal playback speed, every second frame will need to be skipped in order to keep the playback rate at 30fps. But when we slow the clip to 50% and the footage becomes 30fps, each frame in the source clip has a corresponding frame for it to fit in the timeline, so playback is slowed to half speed and it looks smooth. The clip will run for twice as long.

Finally, we have a 24p timeline.

In this case, when the 60p footage is dropped on the 24fps timeline, there is not an even number of frames to be skipped. It's going to need to go something like this: show one frame, skip 2 frames, show 1 frame, skip 3 frames. That can cause some motion to look a bit odd. If we slow the 60p footage down to 50% there will still need to be some frame skipping, perhaps something like: show 2 frames, skip 1 frame, show 2 frames, skip 1 frame, show 1 frame, etc.

Unless you particularly need the output to be exactly half the input, it's better to slow it down to 40%, that way there will be a 1:1 frame match between the source clip and the timeline, and 1 second of 60p footage will last exactly 2.5 seconds on the final output.

Premiere does some frame blending to minimize the effect of mismatched frame counts, but it could never be as good as getting the frames to line up.

I guess I think in film terms, where we assume that the playback speed is the constant, therefore the exposure speed is the reference???
Click to expand...

I think in film terms too. That's the whole point of what I'm trying to say. I hope what I'm saying is a little clearer now.
 
Hi Mike.
Thank you for a brilliant explanation. I am really starting to understand thanks to you breaking it into parts for me.
I was trying to walk before I ran.
This is truly a perspective I have never considered and once again if you do a bit of home work it can really save you some grief. I would never have considered 40% on a 24p Timeline but now with your explanation really do get it.
I shot the ceiling fan yesterday but to get my tiny little brain around it I also shot the timer on my phone .That way I could see something that was constant with a reference to time. 10 seconds 1080 60P, 30P no speed adjustment , then 1080 60p,30p at 60fps. then 1080 24p and finally 1080 24p at 60fps.
Of course I ran out of time to put that into Premiere but on Monday I will try dropping each of those clips onto a 30p timeline and a 24p timeline and try different percentage adjustments. And anything else you think might be a good suggestion.
Thank you again for your patience and great explanation
Tony
 
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