Deceptive capture cards

[numlock]

So far I have tried about 5 digfferent cards and all of them have the same problem. None of them can capture true D1 for NTSC or PAL.

The way I found out was by looking at some footage that I captured from a video tape that had lots of text and when played the DVD that I produced by digitizing this tape I noticed that there were letters missing on both sides.

It turns out that if I select 720 x 480 (or 720 x 576 in PAL) I get fake results. Basically what they do is capture around (+/-)680 and then resize it internally to 720. This is absolute decepion and the manufacturers should be sued for this.

So not only do I not get the full frame size, but I also get wrong aspect ration caused by resizing.

Just FYI I used the following cards:

Navis Pro (MPEG Encoder card)
about four BT878 chip based cards using OEM drivers and also BTWibCAp Open source drivers (these are better but you still don't get the full frame size)
Winnov 1000 PLus
and also the latest Connexant BT881 based card MSI TV@nywhere

Does anyone of a card that doesn't have these problems ? I'm starting to doubt that such a card even exists.

ALso, easy way to find out if your card fits the above description is by capturing a video tape and if you do not see black bands down the left and right side then your card probably belongs to this category...

[mustardman]

Hi,

I own an old DC30+ card, the black bands you talk of are quite thin, I would estimate ~5 pixels or less (both sides). The capture is PAL, 768x576.

I recently got an ADVC100. Its' black bands are much larger, I would estimate 10-20 pixels per side. That does annoy me because it means quite a bit of resolution is lost. It captures PAL 720x576.

It would be interesting to see if the ADVC100 "chops" your picture.

[numlock]

Yes there is a lot stuff that's chopped off.

I did an experiment and captured 640 x 480 and added 40 black pixels on both sides in AVIsynth and then burned a DVD. PLayed it and then copared with the video tape. The result was almost identical with the video tape except I could see a little black line on the left. So I'd suspect if I catured it @ 660 and then added 30 pixesls on both sides I might be getting very close to the right results.

My question is why are the capture card manufacturers deceiving us by telling us they capture 720 when in reality they don't.

All I want is a card that can give me true 720 x 480 and (768 x 576 in PAL) has audio synced with video and can do uncompressed capture or HuffYUV. Am I asking for too much ?

[numlock]

OK, I think I know what's going on here:

See:
http://forum.doom9.org/showthread.php?s=&threadid=66191

http://www.arachnotron.nl/videocap/site/capture_area2.html

[Arachnotron]

This (http://forum.doom9.org/showthread.php?s=&threadid=65809)
has some pointers in it about how you can resize/letterbox your caps to get the aspect ratio ok again when converting to DVD.

But you always will have black bars on the side, simply because the active area on tape will be 52 µs PAL (52.7 NTSC) or even less, while the 720 pixels on a DVD contain about 720 x 13.5 = 53.333 µseconds worth of video. The difference will have to be made up in black pixels.

But I agree: manufacturers should at least give some information about what area of the videosignal their products actually capture.

[trevlac]

@numlock

What is your tape source? A D1 tape player? A dv device will probalby do full PAL 720x576 without skew. You'd have to get a high end card to do full NTSC 720x486. If your source is VHS, it's not D1.

[numlock]

Arachnotron:

I know I will have black bars but that doesn't bother me since they won't be visible on a TV screen anyway. But the main thing is to get the correct aspect ratio.

trevlac:
It really doesn't matter what the source is, the cards will just not capture full 720 pixels.
The solution is to find out what the actual capture area is and then add black borders on both sides to make it 720

[trevlac]

Originally posted by numlock
trevlac:
It really doesn't matter what the source is, the cards will just not capture full 720 pixels.
The solution is to find out what the actual capture area is and then add black borders on both sides to make it 720

My friend.

If you really want to know what one of your BT878 card/drive combos are doing, ask Arachnotron about a handy little calculator. I used this to learn the topic myself. :) With some tools you can read the registers in the chip as it is ready to capture. Then feed the register values into the calculator and it will tell you what you want to know. At least that is how I think it works. :)

As far as D1 goes: Analog source does not have a full 720 pixels. So the source does matter. D1 is a digital format. NTSC D1 is 720x486. NTSC analog source is 711x486.

I'm not clear if you are interested in PAL or NTSC. For PAL, a DV device will capture the entire picture regardless of the source (analog or digital sizes). For NTSC, none of the devices will capture the full 486 lines. DV will capture the 720 width, and BTwincap will capture the full 711 NTSC analog width as 712.

If you record digital source from an analog out, the sides will be overlaid with an analog sync signal. NTSC DVD (720) --> VCR (711). The DVD player does the chopping here.

Cheers

[Arachnotron]

If you really want to know what one of your BT878 card/drive combos are doing, ask Arachnotron about a handy little calculator.

On my resize page, which you linked above, is a calculator which is an adaptation of Trevlac's version. (If you really want to know how something works, take it apart and rebuild it, preferably in working order. :D )
Trevlac's original version is still available; the link is directly above my rewritten version. His version also gives some DVD resizing advice. Or go here (http://www.arachnotron.nl/videocap/site/BT878calc.html) if you want to go there directly.

Note that my site is still under construction. If something moved, go to the root page.

[trevlac]

@Arachnotron

You aren't suggesting that I get a soldering iron for christmas, are you? My family doesn't see me as it is. :D


I couldn't find the references to the tools needed to read the registers on your page. So here is an updated advice version I played with. It covers more than DVD. PS: Take my advice with a sip of beer. After reading it myself, it's clear I can not spell. :)

http://trevlac.us/BT8x8calc2.htm


Must have been a pain to get rid of that directNic junk. :D

[Arachnotron]

I couldn't find the references to the tools needed to read the registers on your page

Sorry, I forgot. They are there on my page, but if you jump directly to your calculator you miss them. I have modified it, so your calculator is now hosted in it's original form on my site too. The downloads point to my site in case your's goes down.

Getting rid of the directnic stuff was easy. Now figuring out the bitshift stuff for the CROP register. THAT took time :D (and learning enough Java to change anything. Long live O'Reilly :) !)

[numlock]

What about vertical croping/centering ? Is this something I have to worry about also ?

[trevlac]

Originally posted by numlock
What about vertical croping/centering ? Is this something I have to worry about also ?

Not a problem on PAL. For NTSC, no consumer digital format supports 486. I believe consumer analog formats are impercise on the active lines also. None of the standards I've read seem to make the number of active lines that clear anyway. Besides, the cards do not stretch the picture on the vertical. As far as the center thing goes, you could get the BT878 spec and work with the registers yourself. Be aware that whatever plays your source may also be a bit off on both the vertical and horizontal centering. So I wouldn't really worry about it. Most people would tell you the entire problem is a non-issue.

PS: I'm hardly an expert in this stuff. I just found out what you noticed, a few months ago. Since then I've done a bunch of reading on the topic. Most people don't seem to be aware, or don't care.

:)

[mustardman]

Trevlac:
I'm not clear if you are interested in PAL or NTSC. For PAL, a DV device will capture the entire picture regardless of the source (analog or digital sizes). For NTSC, none of the devices will capture the full 486 lines. DV will capture the 720 width, and BTwincap will capture the full 711 NTSC analog width as 712. Thank god I'm using PAL:) What do you mean the ful 486 lines are not captured? Does it replace lines with black, chop lines off, add extra lines in????

And analog... it is after all an analog signal, and can have as many sample points as you want in the required time (like audio sample rates - it only affects the bandwidth). If you were a real quality freak, I suppose you could sample at >1000 pixels.

Is what you mean, using square pixels, to keep the aspect ratio right, you would have to use 711 pixels?

In PAL land, 720x576 is standard, but the pixel ratio is something like 1.066666... The "analog" standard is 768x576 which has an aspect ratio of 1.0000...

There is another PAL standard which uses CCIR601 pixel ratio, but I never use it and can't recall any figures.

[scharfis_brain]

PAL has 702 active Pixels corresponding to 768 Square-Pixels
720 Pixels are representing about 788 Square-Pixels
this means, that the PAL-PAR is 1.094 and NOT 1.066666

1.066 does not exsist.

[trevlac]

Originally posted by mustardman
Thank god I'm using PAL:) What do you mean the ful 486 lines are not captured? Does it replace lines with black, chop lines off, add extra lines in????

Chops lines off. DVD requires 480. No need to 'replace' them with anything. Not really a big deal, but I was trying to clearify because numlock was talking D1.


And analog... it is after all an analog signal, and can have as many sample points as you want in the required time (like audio sample rates - it only affects the bandwidth). If you were a real quality freak, I suppose you could sample at >1000 pixels.

Analog is not magic. It has limited bandwidth. It is doubtful that more than 640 samples gets you anything. I'd say that greater than about 540 is the limit of most analog source. (DVDs and DV would be higher). So if you were a real quality freak, you'd be wasting your time with more samples. It'd be better to spend more time on post capture filters.

PS: A BT878 does sample > 1000. In fact it does 1844 for PAL. Then it low pass filters the samples digitally, and throws out 1/2. It oversamples not to get more info, but to reduce the risk of aliasing (digital noise) before it can filter. The filter effectively limits the resolution to 640.


Is what you mean, using square pixels, to keep the aspect ratio right, you would have to use 711 pixels?

In PAL land, 720x576 is standard, but the pixel ratio is something like 1.066666... The "analog" standard is 768x576 which has an aspect ratio of 1.0000...


You have a few misconceptions here.

711x486 is the pixels size of the active picture on an NTSC 4:3 TV, assuming the pixels were sampled at 13.5MHz. AKA, that is the size of a normal picture at ITU-601 sample rate.

702x576 is the size for PAL.

720x576 is the full frame size of Digital (601) PAL. It will not fit on your TV. When it is turned into analog by your DVD player, you get 702x576. Try to capture a DVD with a DV device and you'll see this.

768x576 is 4:3. This is also the size you would want for a PC to view a full PAL capture. Because PC pixels are square and PAL TV pixels are short and fat. As kindly mentioned, 702*1.094 = 768. As far as 720 on a PC. Maybe if you capture DV with firewire.

Hope it's all clear now.

:D