|<font face="Verdana, Arial" size="2">Originally posted by Larry Davis:
How can someone know how a show was filmed? Meaning at what frame rate? I'm curious as to how shows like the X-Files and Soprano's are filmed.</font>
Sometimes you can find out from the flags on the disc. Unfortunately, finding out what the flags are requires a tool that can tell you. There are commercial tools that do this, but they tend to be really insanely expensive. Stacey and I have such a tool, but we can't release it.
Another way is to do some detective work with a software DVD player. In general, most players tend to show you one MPEG picture per freeze frame. So if you step through a chunk of the DVD a frame at a time (using the T key on PowerDVD; not sure about WinDVD), and watch for the seconds indicator to tick over, then start counting frames until it ticks over again, you should find out how many separate images there are per second. There might be accuracy issues with the counter, so it might be worthwhile to do several seconds and average.
However, on many discs, the software won't do the pulldown using flags -- it will just be dumped on to the disc as 60 field per second video. You'll see 30 frames per second, but several of the still frames will be combed. In this case, you have to look at the number of combed frames, and figure out what kind of pulldown was used to create the 60 field per second master. (Make sure to use "force weave" when doing this test, to ensure the combed frames stand out.)
If you see 2 combs in a row every 5 frames, that's 3-2 pulldown, and the source was 24 fps.
For 25 fps, the pulldown is going to be 2-2-3-2-3, so you'd get 2 combs in a row every 6 frames, or possibly 3 combs in a row every 6 frames, depending on where they start the sequence (they could do 3-2-2-3-2, for example).
For 30 fps, there is no pulldown, so you'll just get 30 clean frames.
For video shot with a camera, you'll get 30 frames, all with very small combs.
|<font face="Verdana, Arial" size="2">Another thing I'm wondering, is how does this transfer over to DVD? Meaning, let's say a show is filmed at 30 fps, and transferred to NTSC DVD. Is this going to be transferred and flagged as 24 fps (film)? Or transferred and flagged as 30 fps (video)?</font>
Certainly they're going to try to preserve all the frames, but there's no guarantee how they're going to do it. Keep in mind that there is no standard for flagging "film" on a DVD. The 3-2 pulldown sequence is just a convention. There's no "original frame rate" field on a DVD, and no flag that says "this was from film." At least, there's no flag that is required to be used.
For a 30 fps film, if you're lucky they'll transfer it as 30 MPEG pictures, all with the "progressive_frame" flag set to TRUE. But in practice, I imagine they'd leave the flag set FALSE, because most of the encoders aren't that smart. They see 30 fps; they assume video. So on an HTPC, the vertical filtering algorithm kicks in, and you lose vertical resolution.
For a 25 fps film, they might recreate the pulldown (2-2-3-2-3) with flags, keeping the progressive_frame flag TRUE. But more likely, the master tape they got from Europe gets transferred to an NTSC master, generating the pulldown at that time, and by the time it goes on the DVD, it's just flagged as 30 fps video. Again, the video deinterlacing algorithm then kicks in, and you lose vertical resolution.
What is interesting, and I never have thought about this before, is what does a good deinterlacing chip, like the Silicon Image, do with a 2-2-3-2-3 pulldown sequence? Does it recognize it as 25 fps film converted to 60 field video? If so, that's damn good. My guess is that they do, based on conversations I've had with the engineers. They have a library of weird pulldown signatures, and they try very hard to handle them all. I'll ask Silicon Image specifically about this particular situation.
|<font face="Verdana, Arial" size="2">I find this to be very, very interesting. I have Farscape on Region 2 PAL DVD. The show is shot in Australia. At 100 Hz (25 fps x4), camera pans and motion are quite fluid. I have viewed the exact same episodes on a Region 1 NTSC DVD at 72 Hz (24 fps x3). Motion didn't look smooth at all and appeared out of sync and jittery.</font>
I think your theory makes a lot of sense. It could be, however, that 100 Hz is just so high that anything would look smooth. It would be worthwhile trying something that isn't easily divisible by 100, and seeing if it looks smooth as well. I read a paper by a researcher who said that if refresh rates got over 75 Hz, then pulldown ceased to matter, because it was over the flicker-fusion frequency or something. But that may not be applicable to this.