Posted 31 October 2006 - 10:09 PM
Posted 02 November 2006 - 08:01 PM
Posted 02 November 2006 - 11:08 PM
well, as the name indicates it changes the shutter speed, which is how long each frame is exposed. the frame rate indicates how many frames are shot per second but says nothing about how long each is exposed.
thanks for the reply, and I see what you're saying. In film cameras frame rate and shutter speed are one and the same. As you know 24 FPS is 1/48 of a sec shutter speed. When you lower the shutter speed (and create longer exposure time) you get a similar result to a film camera shooting at a slower shuttter speed, but not when you go faster speed. I was hoping some one could provide some insight into the more technical aspect of the compression. I guess I should have been more clear on that. Sorry.
Posted 03 November 2006 - 01:30 PM
not really, that's assuming you got a 180 degree shutter. many cameras have 150 degree shutter, which results in a shutter speed of 1/60, and many have variable shutters where you can change the angle and thus the shutter speed to whatever you want, as fast as you like and dows to almost 1/24 after which you'll start seeing the streaks from the pulldown.
In film cameras frame rate and shutter speed are one and the same. As you know 24 FPS is 1/48 of a sec shutter speed.
oh, you mean when you go slower than the frame rate? as a matter of fact that *does* change the frame rate of the video, it's just that frames are duplicated. there's no other technical possibility. variable frame rate video and hd cameras fo the same, and then you remove the duplicates in post.
When you lower the shutter speed
i just realised that there's actually the possibility for a camera to create full frame rate long exposure but that would require a ccd which you can start reading from again when the previous frames were still being read. or it could be done all in the dsp, using frame blending, but that would create artifacts. this is definitely something i need to research the next time i have one of those cameras...
Posted 04 November 2006 - 03:22 AM
Posted 04 November 2006 - 08:47 AM
Yes -- assuming 180 degree shutter -- that's great that you know so much about film cameras, but you haven't answered my question. I didn't start this thread for a intro to FILM lesson. Clearly the camera is duplicating frames to approximate what a longer exposure time would be -- so what is it doing when the shutter speed is increased -- compression wise; how does it affect the long-GOP. It's obviously not throwing out frames? It's not writing more data either now is it? so what is it doing to the structure of the MPEG-2 files? Thanks for trying, but I don't think you know
It's hard to tell exactly what you're after. You started with a series of wrong assumptions and Matt tried to dig you out from under them. Now perhaps you should change your tone and start over.
Posted 05 November 2006 - 09:59 AM
of course i do. it compresses this stream just as it would any other stream. the recorder part of the camera doesn't care what the camera part is feeding to it. it's just a sequence of frames either way. no frames added, none dropped, no change in the gop. this is so obvious i'm sorry i didn't realize it was a question.
Thanks for trying, but I don't think you know
Posted 06 November 2006 - 03:06 AM
compression wise; how does it affect the long-GOP. It's obviously not throwing out frames? It's not writing more data either
what is it doing when the shutter speed is increased
I was hoping some one could provide some insight into the more technical aspect of the compression. I guess I should have been more clear on that.
What exactly does this function do
this is so obvious i'm sorry i didn't realize it was a question.
It's hard to tell exactly what you're after.
Thanks for the help.
Posted 12 November 2006 - 05:28 PM
Hope it clears things up,
Yecid (all the way from Bolivia) Jr.