ivtc'ing a 1088i 30fps source

[Nothingface]

hello all...

i am new to the forums but have been reading here forever, i would like to thank everyone 'first off' for the wealth of knowledge and speedy information i get from reading the site.

recently i have been experimenting with alot of 1088i streams 'typically imax stuff' and my main question is revolving around ivtc'n these 30fps streams. i am using XviD pretty faithfully now because there are some aspects i like more about xvid over divx, mainly the tweakability.

one thing i surely know is 1088i thru 720p is shot in 30fps sometimes 60fps, and it was suggested to me that i ivtc a 1088i stream... is that such a good idea ? expecially for an imax film ?
i can seemingly notice the frames that are missing /or visual information to the eye, mostly during hi-speed or time-lapse scenes and fly-over scenes.

i have recently had 'some' luck converting a 1088i stream to 1080i without the grey bar (thanks projectX) then from that point further reduced the stream to 720p using roku-720p so i could do the encode with XviD. my main goal here is to get a 1088i stream into 720p (no grey bar) with the least steps as possible so i can encode the 720p stream in xvid w/ hi-rez and i am weary about ivtc'ing these streams because i know frames will be lost.

my main questions would be...

1. can i projectX a 1088i "grey barred" stream in 1 step to 720p 'no bar' ?

2. is ivtc really a good idea for imax with alot of timelapse and hi-speed type fly-over scenes ?

thanks guys for any direct help, i have been reading so much here my head is about to explode ;)

[manono]

Hello and welcome to the forum-

1. I don't know. Someone that's used ProjectX will have to answer.

2. one thing i surely know is 1088i thru 720p is shot in 30fps sometimes 60fps, If it's a movie, then that's not true. They are shot with 24fps film cameras. I don't know what the Imax process uses (although I sincerely doubt it's 60fps), but it's easy enough to find out. What they're broadcast at (30 or 60fps) is often very different from what they were created at (24fps for movies). Do you have a way to open them in something in order to advance a frame at a time? I'd do it by making a Movie.d2v project file in DGIndex and then opening it in Gordian Knot. If you can find a place with movement, and then advance a frame at a time, if it's originally 24fps, you'll see duplicate frames every 5 frames, and it should definitely be IVTC'd. If it was broadcast at 30fps, and also created at 30fps progressive, then you won't see dupe frames, and you should leave it alone. If it was broadcast at 60fps, but created at either 24fps or 30fps, then you'll also see dupe frames, and you should also get rid of them.

[Nothingface]

Originally posted by manono
if it was broadcast at 30fps, and also created at 30fps progressive, then you won't see dupe frames, and you should leave it alone

thanks for the welcome and reply...

i did kind of make a typo in #2 where i said "shot @ 30fps" actually what i did mean was "brodcast @ 30fps" i myself have yet to come across a 60fps broadcast in transport.

i guess i was kind of looking for confirmation about turning a 1088i stream @30fps into a 24p stream @24fps would be loosing information/frames. and that was causing a funny type of playback, where most scenes appear to be smooth but if you look at distant objects in the final convert to xvid, i can notice something strange like pausing effect or frame dropping (hard to explain)... but the specific convert i am refering to appears to play smooth with only minor hard-pausing during playback, but there is something missing or being discarded specially during the hi-motion scenes that my eye can pick up anyway.

thanks again...

(your quote above is pretty much just what i was looking to hear about the process)

[manono]

Hi-

i did kind of make a typo...

You and me both. I didn't notice I had misspelled "Hello" until you made it big and boldfaced. It's fixed now, but will remain wrong in your quote.

where most scenes appear to be smooth but if you look at distant objects in the final convert to xvid, i can notice something strange like pausing effect or frame dropping (hard to explain)...

I suppose the foreground action could be 24fps, and the background could be CG 30fps, in order to give that effect. Hybrid video can be very tricky to handle. But you have to examine it thoroughly beforehand to be sure of what you have, before IVTCing.

but the specific convert i am refering to appears to play smooth with only minor hard-pausing during playback, but there is something missing or being discarded specially during the hi-motion scenes that my eye can pick up anyway.

Do you have a powerful enough computer to play it back smoothly? During complex scenes (high action scenes), playback of high-res stuff needs a bear of a computer to play smoothly. Again, checking the problem areas frame by frame may tell you if it's all there, or if original unique frames were removed during the IVTC, or if it's a playback problem instead.

[Nothingface]

lol... i didnt even notice that typo, but i did fix it.

im am quite sure its not a playback problem, but the convert i am refering to was done by someone else, it could be their machine that lagged on the encoding of the 1088i, they have a tendency to eat alot of processor power during encode.

my box is pretty new...

intel - lg775 - 3.2ghz - p4
asus - p5ad2_premium - mobo
ati - rx800xt pci-E card "mci"
2gig ddr2.DualChann - pc4300 - centon (not bad mem first time w/ it)
initally i purchased 1.5gigs but wanted to run dual chan so i went and bought the other 512.stick.
pioneer dual layer dvd x16 burner.

i have been observing the frames via Vdub and a few other apps, but i cant seem to notice the doubles every 5 frams or so that you refered to. also these imax hdtv i suspect are newer releases from imax because i am not used to seeing them before. i will have to do some reading on the imax process to find out a little more how they shoot the movies "specially the newer one" and see what i can come up with. i think someone suggested i ivtc the files so it would make an easier encode by dropping that extra 5fps ? but i may just have to experiment and see the outcome.