Anyone else exploring mjpeg @ 48fps?

M

modulr

Active member
I enabled mjpg 30fps -> xfps ... set it to 48. Took a clip, loaded it in Apple's Dumpster tool...
ftp://ftp.apple.com/developer/Quicktime/Tools/Programmers_Tools/Dumpster.dmg
(it lets you edit QT headers)

Set moov -> mvhd -> timescale from 48 to 24
Set moov -> trak-> mdia-> timescale from 48 to 24
Saved (it's lossless, since it only modifies the header)

Resulted in a 24P clip with no frame skipping. Problem is, I can't get it to record more than 10-15s. Bitrates for what I would consider normal footage is average 50Mbps at 24p, but exceeds 100mbps at 48P... but it seems when even the factory setting, it's just not fast enough after 15s or so. D'oh!

Anyone else experiment along these lines?
 
sammysammy said:
what shutter speed are you shooting? to get that , 80,90?
Click to expand...

1/50th @ 48fps. -> modify header -> 24P

I've done more exploring with the quality/table numbers, but I just can't get it to record more than 15s without a write speed error. Kinda strange in that even at 48fps, I can set the bitrate well below what you'd get with an extreme 30fps setting. Kinda odd.

For got to mention, using Sandisk 8GB Class 10
 
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Interesting... if this works, this could be a way to get 24fps MJPG with minimal rolling shutter. Plus, you'd always have the ability to jump back up to 48fps for 2:1 slow-mo when necessary.

Where my Pappas at? Dude should be all over this! :thumbsup:
 
ok..i just tried this..modulr to me it seems that the clips are faster(not in real time, a second is not a real second of recording) and not in real time when i go over 30fps ,did you also find that?
Barry,so we get a much cleaner 24p from 48fps (at 1/50?) rather than 30p to 24p?
 
Looks like I'm off somewhere in what I thought was happening. I just shot a slate to verify the timing. It appears to be recording at 30p, but setting the header info to 48. So at 48, it plays back fast.. but my initial thoughts were it was actually by some luck 24 when the header was modified. :(

I'm guessing, the camera just shoots 30p in Mjpeg regardless. If the frame rate is over 30, it just sets the headers to whatever that frame rate you've punched in ptool, but it still records 30p. If the framerate is below 30, it drops frames.

Now why the camera stops when using 48fps makes no sense.. because if this is true, the frame rate hasn't actually changed. Hmmm.
 
yea..thats what happened with me...seems to be not a true 48p..im guessing that 24p on mjpeg will be very tough..i hope it comes true..
 
Barry_Green said:
Interesting... if this works, this could be a way to get 24fps MJPG with minimal rolling shutter. Plus, you'd always have the ability to jump back up to 48fps for 2:1 slow-mo when necessary.

Where my Pappas at? Dude should be all over this! :thumbsup:
Click to expand...


Lol..... This is very interesting- I have been wrapped up with the AVCHD these past few days. Now I need to try this out. 48fps is also very interesting too..... Good over crank feature.

Do we have a clip from this test?

What can't this camera do- Next were gonna find out this camera makes roast beef sandwiches...

** EDIT**- Just noticed the last posts. Oh well. The AVCHD is so good that it's hard to beat.... My recent settings of 58-60-68 at gop15 24PN have been very sharp/stunning- I can't complain..

Pappas
 
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modulr i have tested 30fps to 50fps, and it stop recording just after 15 sec with card speed error.

my settings are for the test: only battery , time limit and version compare selected. Obviously and 30 to 50 fps.

Tried with 422 and with out and same time limit. (15 sec)

all videos shows 50fps but how can i be shure they are that fps and not 30???
 
In all likelihood it's not 50fps. The header might suggest it's recorded at 50fps, but odds are when you play it back, it will be sped up.. suggesting it's recorded at 30fps unfortunately.
 
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