Possible to capture at 23.97?

[Marty2003]

Umm, here's my problem. I don't have a dvd drive on my computer, so this is my dvd capture setup. It's a sad setup, but anyway...

I have a winTv capture card which I use Vdub to capture. My dvd player is hooked up to my vcr using RCA wires, and my vcr is then hooked up to my capture card using a coaxial cable. I usually just make low quality (352x240) vcd's from dvd's. I'm not that picky about quality.

My problem is this, I can't capture at 23.97 fps. DVD's are 23.97 fps, but If I try to capture at 23.97 I get massive dropped frames. I cap at 29.97 and get one dropped every once in a while, which is normal. What's going on here? I'm guessing the vcr output's the video at 29.97 by doubling some frames because if I look at the video every 4th frame is repeated. 1-2-3-4-5, frames 4 and 5 are the same. I can't connect my dvd directly because it only has s-video and RCA outputs, and not a coaxial. my WinTV card has an RCA for the video, but none for the audio.

Is there some way to either capture at the right frame rate, or remove the duplicate frames somehow. If I encode the mpg with TMPGEnc at 23.97, I have no guarantee that it will drop the right frame. If originally 1-2-3-4-5 dropped frame 3 I would get 1-2-4-5 and 4=5 so I would get jerky video.

Also, this isn't really related, but does anyone know how vDub handles dropped frames. say I cap a 1 minute clip at 29.97 but I drop 30 frames in the capture. Is the result actually 59 seconds, or does Vdub duplicate the previous frame and place it where the dropped frame would have been?

[Nelson37]

Although you are basically correct that DVD video is at 24 fps, it must be captured at 30 fps. The frame duplication you are seeing is called TELECINING, and it is caused by a Pulldown flag which is embedded in the video, which tells the playback device to perform the Telecine operation.
The sole purpose of Telecining is to convert 24FPS to 30FPS for TV.

These frames are NOT actually duplicates, but by capturing at X240 and throwing away one-half of the video information, they will appear identical.

The only way to cap at 24 fps is to perform a real-time InVerse TeleCine.

A truly Progressive player with a progressive DVD would correctly cap at 24 fps, but this is not that common yet, SFAIK.

[PigOnWing]

I'm afraid you might have some misconception regarding the fps issue, which is at the heart of understanding what's going on.

While the source material on DVD films is many times encoded at 23.97 fps, once broadcasted it is always broadcasted at 29.97 fps (for NTSC; 25 fps for PAL).

The issue is this: in order to make the encoding both more efficient and true-to-the-source, if a source material is FILM - as in, 'cinema film', which is always filmed at 24 fps - the full original frames are encoded into the MPEG stream, as-is.

But broadcasting (that is, the process of transmitting to a TV set, regardless if it's a broadcasting station or your home setup) can only be done at one of two setups: NTSC (if you're in the US or Japan) or PAL (if you're in Europe and most other countries). Which, as far as frae rate goes, is either 29.97 fps or 25 fps, respectively.

The process of converting a film, from its original 24 fps format into TV's-29.97 fps broadcasting format is what is known as 'Telecine'. As this issue has been thoroughly explained in many articles in the past, I see little point re-describing it here; just make a search for 'Telecine' either here or in Google. Bottom line is, that it's a pure technical process, which 'splits' the full frame into two 'half frames' and then duplicates some of them, in order to accomodate the necessary by standard 29.97 fps. As the process is pretty simple, the DVD can do it 'on the fly' for you, while retaining the original, Un-Telecined material within the MPEG stream on the DVD itself.

So, in effect, once you're broadcasting (and that is, effectively, what you're doing, once you hook up your DVD player using any cable into your VCR, TV, Capture card or any device using analogue signal), the material is already in 29.97 fps format. The fact that the MPEG itself is, at its heart, 23.97 fps, doesn't come into it; it can only apply when you rip the actual MPEG data, using a DVD-rom - which doesn't involve any 'broadcast' functionality. AFAIK, even software DVD players like PowerDVD & WinDVD, while in theory they can play the original 24 fps material on the PC's screen (doubling every frame, going for 48 double-fps - as is done in cinema, actually), don't really do it: They, too, abide the '23.97 should be played as Telecined 29.97 fps' rule.


The dropped frames that you get are, in effect, frames which VDUB knows that are there - but which it misses - as simple as that: you set it to capture 23.97 fps; it sees 29.97; in effect, it knows that every 5 out of 30 frames, it misses - it 'drops'.

While you can, in effect, set your setup in a way that you'll eventually get the original 23.97 fps, this would be a tedious and totally unworthwhile process. Although you can, in theory, capture at 29.97, then run the result through Inverse-Telecine (look it up in the site), this is a process usually worthwhile to do when you have no better source to go with (as in rare films on VHS, or material originally filmed using cinematic equipment but released only through TV) - do consider that this is something usually done by 'quality freaks', who would rather have better use for the allowed Mbps on the VCD stream rather then have it wasted on 'duplicate' material. On the setting you describe - having the DVD analogue signal go through the VCR, then outputting an analogue signal again from your VCR to a capture card, then having your Capture card re-converting that already-tired analogue signal back to digital form - the amount of signal-loss and added artifacts (also caused by the limitation of the broadcasting) make the extra-hype of 'going for 23.97 vs. 29.97' so negligble that it wil actually sound like a tasteless joke, at best.

Again: what you do, the moment you transfer an analogue signal, is broadcasting, and having the picture quality suffer from all limitation of the NTSC broadcasting system.


Even though I expect that's the last suggestion you'd like to hear here - may I suggest, that instead of beating the DVD's signal up so much, spending that much amount of time capturing, then tweaking and re-encdoing a captured analogue signal for an already-encoded-at-optimum-condition MPEG stream, you might want to consider... buying a DVD-ROM drive?

-- Piggie

[Marty2003]

Thanks for the information. I already knew about telecine, but I didn't think that was my problem because there was no interlacing between the frames. I neglected to take into account that 352x240 will never be interlaced but you guys still cleared things up Now to answer my own question, Telecine changes fields AA BB CC DD into AA BB BC CD DD. Since I'm only capping at 352x 240 only one field is being used, so basically I end up wil A B B C D, which looks like two frames are being duplicated. I would buy a DVD Drive, but I'm a real cheap-ass

[PigOnWing]

Indeed, a frame is being duplicated (Two frames had you captured both fields). Moreover: Both fields are different parts of the same field, so basically, by capturing one field, you discard half the frame.

There are tools to discard the extra frame, which is part of the process of Inverse-Telecide; again, that process would be tedious for an already beat-up signal, which is the result of what you describe.

While I truly and honestly appreciate your statement of being a cheap-ass (many of us are, some of us are less keen to admit it) - might I point up the mere fact, that the cost of a DVD drive (around $50, these days?) is waaaaaaaaaaay down the cost of the hours you'rs spending capturing, cleaning and now, as you might suggest, going for inverse-teleciding a poorly, weak, beaten-up signal?

I stopped buying groceries at 'Ultra-Cheap Grocery Centres', which saved me roughly $30 a month, when I made the calculation that my expenses getting there (in Gas, parking, time and headache) well exceed $40. I tend to get the feeling that sometimes people strive for the 'cheapest-by-all-means solution', no matter what are the costs.

Just my $0.03 (inflation, you know).

-- Piggie

[Epi]

If your looking for a DVD Drive cheap to end you capturing woes, heres one that's available from Dell:

http://accessories.us.dell.com/sna/ProductDetail.aspx?category_id=193&keyword=&mnf=&pr...=19&iCompatid=

It's only $37.45/€34.42 pretty good deal if you ask me.

-Epi