Does 50p -> 50i use frames->fields?

fausseplanete wrote on 9/23/2008, 6:56 PM

If Vegas 8.0c is given 50p media and the Project is for 50i, will it (I hope) take alternate fields straight from alternate frames of the 50p?

Comments

TheHappyFriar wrote on 9/23/2008, 7:23 PM

it will, but in interlaced footage each field is 1/50th of a second different. So a moving object is in different spots in each field. Progressive doesn't have this, so you'll end up with two fields that are identical each frame.

Which is what progressive is.

megabit wrote on 9/24/2008, 12:53 AM

IMHO, one would say that rendering 25p to 50i simply creates 25PsF - I am using this each time I make a BD, as 25p is not in the specs.

The 50i output files from Vegas still play back as progressive - never saw any motion jaggies.

farss wrote on 9/24/2008, 2:31 AM

If you shot 50p then if Vegas is doing it correctly you'll get 50i.
It should take one field from each frame to yield exactly the same result as if you shot 50i in the first place.
My only concern would be that your 50p could have too much vertical resolution for 50i and you could get bad line twitter but that depends on a number of unknown factors.

Bob.

megabit wrote on 9/24/2008, 3:06 AM

Oops... Bob's reply made me realize I didn't read the original one carefully enough; it's about 50p not 25p. Sorry!

TheHappyFriar wrote on 9/24/2008, 9:23 AM

I assumed he mean 50p = 50i, just not interlaced. Did he really mean 50 progressive frames per second to 50 interlaced frames per second, or 50 progressive frames per second to 25 frames per second (25 upper fields per second, 25 lower per second).

:??????

farss wrote on 9/24/2008, 3:54 PM

I'm assuming he does mean 50 progressive frames per second into 25 interlaced frames per second.

Reason being is this has come up elsewhere as the EX1/3 does shoot 720p50 and those shooting it oftenly also need 50i (25 interlaced frames per second) for distribution.

Bob.

fausseplanete wrote on 10/1/2008, 1:53 PM

Yes I did mean 50 progressive frames per second into 25 interlaced frames per second (="50i") for distribution.

Apart from the stated EX's 720p50, if you put 50i original footage through AviSynth's TDeint(Mode=1), which uses motion estimation to turn each field into a complete frame, you get 50p. Motion estimation is the best form of deinterlacing. So-obtained progressive is a good basis for resizing (e.g. scanning at SD within HD). Double framerate is good for obtaining smoother slomo (e.g. by stretching). Also I hope it is beneficial to obtaining god interlaced product. At least it seems the extra information does get used, helpful (though not completely sufficient) for obtaining a good quality end product - I guess I can only experiment.

..at the expense of longer rendering of course.