Interlacing 25p to 50i in Vegas 10

[Gabor Heeres]

Hi All,

Some will call me crazy but I'd still like to do the following. I would like to interlace the 7D's 1920x1080 25p video's to 50i using Vegas 10. Because I understood the 7D records at a higher bitrate than 35 Mbps for now I have chosen to do this using the XDCAM EX MXF-codec, but is there a better way? Any help is welcome.

Gabor

[Jack Zhang]

This is very important. For all your clips, you must choose "Disable Resample" to avoid ghosting.

Try the XDCAM EX MP4 option. It allows direct import into XDCAM Browser in case you're working with both XDCAM and 7D footage. MXF files produced by Vegas are notorious for compatibility issues for everything but Vegas. The MP4 option makes the file far more compatible.

[David Jimerson]

You shouldn't see any ghosting going from 25p to 50i. Ghosting happens when you deinterlace and try to combine two fields, two separate moments in time, into one. The ghosting represents a moving object in two different places. You're doing the opposite here; you're not combining any two moments in time, so there's no ghosting.

You haven't said you plan to deliver this footage, but really, all you have to do is render out to Blu-ray 1080i. It will be best to edit on a 1080/50i timeline.

[Jeff Harper]

I'm trying to figure out why someone would want to interlace progressive footage. Can anyone explain to me when and why one would want to do this?

[Gabor Heeres]

Thanks all for the help. Because the 1920x1080 50i 35 Mbps XDCAM EX MXF's produced by Vegas work fine when uploaded to the clients let's keep it that way.


Jeff,

Very easy, because the client wants it that way.... In the TV-world (especially news....) there are still a lot of incompetent people running around. At least here in the Netherlands.... If they want it 50i they get it 50í, I've stopped starting useless discussions with those people over and over again. They run 50i on their own cameras so they want freelancers to deliver it the same way. Not because they really know something about it, just because they are used to it. Same with the form factor issue, a lot of TV-producers still think a 'big' camera is always better than a handheld one. When I showed up with an EX1R for a short TV-quote last week it was no good, my goodold DSR-250 saved the day..... Now tell me which of those two is the better camera in all aspects.

Gabor

[Jeff Harper]

They say the customer is always right. Thanks for explaining that Gabor, it was driving me crazy!

[Phil Lee]

Hi

Originally Posted by Gabor Heeres

Hi All,

Some will call me crazy but I'd still like to do the following. I would like to interlace the 7D's 1920x1080 25p video's to 50i using Vegas 10. Because I understood the 7D records at a higher bitrate than 35 Mbps for now I have chosen to do this using the XDCAM EX MXF-codec, but is there a better way? Any help is welcome.

Gabor

You can't do it. 25p is completely different to 50i, so you can't turn one into the other.

25p is 25 samples a second, this is similar to films 24fps, and so it contributes to the "film effect". Typically unless you shoot carefully the playback of motion and camera pans will judder, and it can be hard to watch.

50i is 50 samples a second, with each sample only being half the resolution (a crude compression system introduced decades ago for TV broadcasts). With 50i you have twice the temporal information (motion information) than 25p, this gives much smoother motion and is why video is video.

Once you have 25p, you can't recreate another 25 samples per second to get 50i.

Now you can store 25p as 50i, this has been done for decades and is still routinely done today and is called PsF, progressive segmented frame. For example the BBC only want 50i delivered to them, so a 25p drama is sent to them as 50i. The crucial point with this is once that 50i reaches a TV, it becomes 25p again, so you haven't converted 25p to 50i, you've just temporarily packaged the 25p in a 50i container.

To convert progressive footage to same interlaced equivalent, you need the same sample rate. So if you had 1080/50P which is 50 progressive frames per second, you could convert that to real 50i.

Regards

Phil

[David Jimerson]

My guess is the client doesn't care about the motion, just the format.

[Marcus Martell]

Guys very interesting 3D! What about of i Have 3 different frame rates on the time line like 50i, 25p and 24 p! What's the best solution to render?
Thx

[Prech Marton]

"Once you have 25p, you can't recreate another 25 samples per second to get 50i. "

Why? For example interpolating between frames gives smoother motion.
But i also don't find a solution in Vegas for this.

[David Jimerson]

Because you only shot 25 samples per second. That's all the information you have to work with.

[Prech Marton]

What about twixtor, what about frame blending, what about frame interpolation?
Software can guess what's inbetween the frames..

[David Jimerson]

Neither frame blending nor frame interpolation will draw totally new frames that "should" have gone in between. Blending is particularly bad at this -- you get tons of ghosting.

I've never seen anyone use Twixtor to give a slower frame rate the motion signature of a faster frame rate. It works fine the other way around, but not that way. But if someone has examples, I'd be happy to see them.

[Prech Marton]

Ok.
My LG Cinema tv can create beautiful 50fps smooth motion from 25p footage.

[David Jimerson]

Yes, the TVs are able to do that (though it's aesthetically criminal when it comes to films). Neither Vegas nor Twixtor nor any other software I'm aware of can.