Capture Karten und aspect ratio fuer Dummies ;-) (german!)

[Ookami]

Capture-Karten und aspect ratio fuer Dummies ;-) 1.0 by Der Karl:

[ohliuv]

nice document :D

[Wilbert]

It can be found here: (...)

edit: I removed it again. But I will translate it one day :)

[BaronVlad]

Thanks for bringing it up again Wilbert. To save your traffic it also can be found here:

http://guides.videoxone.de/derkarl/index.html (HTML and PDF Download) :)

[erratic]

I have used a few extracts from Der Karl's document to explain the difference between PAL 720 and PAL 704 in Dutch, based on my experience with a Radeon All-In-Wonder 8500DV card. If you have an ATI/Hercules Radeon card the correct full PAL resolution is 704x576 and not 720x576.
http://users.telenet.be/erratic/capture/resolution.htm

[Arachnotron]

see this site for other info about this issue:

http://www.uwasa.fi/~f76998/video/conversion/

@erratic:

Nice translation/explanation! I just opened a thread here: (http://forum.doom9.org/showthread.php?s=&threadid=64635) about using a DVD player as a source to determine the active area exactly.

[erratic]

Arachnotron, If I understand the information in your new thread correctly the BT878 chip captures only 696 pixels per scan line with the Hauppauge WDM drivers and 704 pixels with the BTWinCap drivers?
Does that mean 704x576 is the correct capture resolution with the BTWinCap drivers, but with the Hauppauge drivers you actually have to capture 696x576 and add black bars?

I will update my web page (the part about the Brooktree drivers) so it points to the thread you started. This Brooktree and Cx23881 stuff is confusing me. :confused:

Obviousy I was able to test the ATI Radeon part myself and 704x576 looks correct on my TV (720x576 looks a little stretched) so I'm pretty sure I got that right.

[Wilbert]

@erratic,

Some quick comments about your webpage:


Capture als test met je analoge capture kaart enkele clips met een 720x576 resolutie. Als je links en rechts geen zwarte balken ziet (of heel weinig zwart) ben je verkeerd bezig. Je hebt in dat geval namelijk een kaart die niet ITU-compliant is. 704x576 is dan in ieder geval beter. 704x576 kan je correct resizen naar 352x576 (CVD, Half D1) en 352x288 (VCD) maar voor 480x576 (SVCD) moet je links en rechts eerst zwarte balken van 8 lijnen breed toevoegen.

Als je wel zwarte balken ziet die samen minstens 18 lijnen breed zijn, heb je een kaart en drivers die geschikt zijn voor 720x576 (dus ITU-compliant). 720x576 kan je correct resizen naar 480x576, maar voor 352x576 of 352x288 moet je links en rechts eerst 8 lijnen croppen (wegknippen).
Sorry, I don't have time to translate this.

1) You say that if you don't have black borders on the left and right, you are capture at the wrong solution. Personally I would remove the word "wrong". Capture card don't need to capture at ITU compliant resolution. Most cards don't.

2) Looking at 720x576 is not enough to determine if the capture chip is ITU compliant or it isn't. The broadcasting itself can also contain black borders. So, it's better to capture at 720x576 and 704x576. If the latter is a scaling of the first one, than the chip is not ITU compliant.

In the analog capture guide you can find more info (for example, why it's preferable to capture at 768x576).

[Arachnotron]

@erratic,

Arachnotron, If I understand the information in your new thread correctly the BT878 chip captures only 696 pixels per scan line with the Hauppauge WDM drivers and 704 pixels with the BTWinCap drivers?

For PAL, that is correct.

The CX23881 stuff is about a different chip, the connexant cx23881, which is the successor to the BT878/fusion 878 chip. Newer Hauppauge models come with this newer chip. Since it was developed from the BT878 it shares many features.

As Wilbert said, wrong is not exactly the right word. The only thing to be aware of is that a capture made with a BTWincap driver has to be scaled differently then a capture from a Hauppauge driver if you want to keep the aspect ratio correct.

a 720x576 DVD contains information for 53.33 microseconds worth of scanline. A BTWincap capture 52.15, a Hauppauge only 51.56. If you want the aspect ratio to stay the same, you have to compensate for this difference.

[erratic]

Wilbert and Arachnotron,

1) When I write that 720x576 without black bars is the wrong resolution, I mean it's wrong for DVD authoring. That's what my web site is mostly about: DVD authoring, with resizing for Half D1 (CVD) and (S)VCD included. So it's for converting to MPEG-2 and watching it on a TV eventually. Capturing for watching on a PC monitor (in DivX/XviD or whatever format) is not included in my guide. Maybe I should make that more clear.

2) Yes, I do mention in my guide that the broadcast itself can contain black bars. That's why I've added an even better test now: tune to a channel that displays a test pattern, capture that test pattern, author it on a DVD, and compare the test pattern on your DVD with that same test pattern being broadcast on your TV.

As far as 768x576 is concerned, I don't see the benefit in capturing at that resolution for DVD authoring. With an ITU compliant card I would capture 720x576. With my Radeon AIW card 704x576 is correct (768x576 is not even supported). With a Brooktree/Conexant chip it's more complicated apparently: 704x576 is correct if you're using the BTWinCap driver, otherwise you should capture 696x576 and add small black bars (again for DVD authoring).

I'm going to make a few more minor adjustments to my web page now. More comments are welcomed of course.

[Boulder]

Originally posted by erratic
With a Brooktree/Conexant chip it's more complicated apparently: 704x576 is correct if you're using the BTWinCap driver, otherwise you should capture 696x576 and add small black bars (again for DVD authoring).


(a Hauppauge WinTV Theatre, BT878, owner speaking)
So this would mean that I should capture at 696x576 and add 4-pixel borders on the left and right side? After this, should I resize the capture as if it was ITU compliant or non-compliant:confused: I use FitCD to get the correct resizing, it has an option for both cases.

[Arachnotron]

So this would mean that I should capture at 696x576 and add 4-pixel borders on the left and right side? After this, should I resize the capture as if it was ITU compliant

The number 696 quoted here refers to the 696 ITU-BT601 13.5MHz pixels in the capture area used by the Hauppauge BT878/CX23881 drivers. (At least that is what I found. I could be wrong of course :D )

If your target is 704/576 ITU-BT601 13.5 MHz pixels, you are correct. (add 2x4 pixels, no resize)

[Arachnotron]

A word of warning :
TMPGenc ( and a lot of other mpeg2 encoders I supect) in its default settings will cheerfully resize your 704x576 avi to and 720x576 MPG file. This screws up your aspect ratio again.

Beware of Wizards....

[erratic]

Yes, you have to use Full screen (keep aspect ratio). Then TMPGEnc adds black bars to 704x576. With that same setting TMPGEnc resizes 768x576 to 704x576 and adds black bars. But you can avoid the black bars by making a 704x576 MPEG-2 file of course. That's what I would do.

[Arachnotron]

Yes, you have to use Full screen (keep aspect ratio). Then TMPGEnc adds black bars to 704x576. With that same setting TMPGEnc resizes 768x576 to 704x576 and adds black bars. But you can avoid the black bars by making a 704x576 MPEG-2 file of course. That's what I would do.

Yes, I know. What I ment to say is that you have to be carefull with your encoder settings when using a 704x576 source. The default wizard in tmpgenc uses "full screen", which ends up resizing it.

If you don't know exactly what your encoder does, simply adding black bars on both sides until you reach 720x576 might be the safer thing to do...

[erratic]

Yes, you're right, it's always safer to add the bars yourself before encoding.

I just tested TMPGEnc with a 696x576 file. TMPGEnc adds black bars correctly (without resizing the video) if the following settings are selected:

Source aspect ratio: 4:3 625 line (PAL, 704x576)
Video arrange method: Full screen (keep aspect ratio)

But TMPGEnc recognizes a 696x576 resolution as 1:1 (VGA) which has to be changed manually of course.

[erratic]

Originally posted by Wilbert
So, it's better to capture at 720x576 and 704x576. If the latter is a scaling of the first one, than the chip is not ITU compliant.Two more questions about ITU compliant chips:

1. Does this mean that ITU compliant capture chips never scale and only support 720x576 (PAL) and 720x480 (NTSC)?

2. What chip do analog<->DV converters like the Canopus ADVC-100 use? I guess it must be ITU compliant.

EDIT: My assumption in question #1 is based on the statement in Der Karl's document that only 720x576 is ITU compliant for PAL:
Gängige Capture-Auflösungen für PAL sind 768*576, 720*576 und 704*576. Was davon ist nun richtig? Die ITU sagt eindeutig 720*576 !
So that would mean that 704x576 is not ITU compliant even though it's DVD compliant and even if the aspect ratio is correct.
Also, Arachnotron's test includes one card that captures 720x576/480 correctly: the Terratec Cameo Grabster 200 USB v3.05.
He also writes that the Cameo grabster can only capture at 720 pixels horizontally.

[Arachnotron]

Most Philips chips operate at 27 / 13.5 MHz.

From EBU Technical Recommendation R92-1999 for PAL:


The EBU is aware of a certain amount of confusion about the active picture area in the implementation and use of digital signals conforming to the ITU-R Recommendation BT.601 [1].

Recommendation BT.60l specifies a line length of 720 luminance pixels (13.5 MHz sampling).

ITU-R Recommendation BT.470[2], specifies a line length of 52 µs for 625 line analogue signals. This corresponds to 702 luminance pixels.
This apparent difference can lead to difficulties in conversion, especially if users wish to maintain the correct aspect ratio of the pictures.

Recommendation BT.601 accommodates modest variations in the position and length of analogue blanking which arise before a signal is digitised or when digital signals pass through any subsequent analogue process.

The EBU recommends that:

· In 625-line television systems sampled to ITU-R Rec. BT.601 part A, only the central 702 luminance samples of the digital active line (samples 9-710 inclusive) and their associated chrominance samples
should be used to carry the active picture. The remaining 18 luminance samples and their associated chrominance samples may be used to carry picture information only but for no other purpose. It cannot be guaranteed that picture information in these samples will be displayed in either 4:3 or 16:9 aspect ratio images.

· The centre of the picture should retain its position throughout all production processes unless there are creative reasons to deliberately do otherwise.


So, if I understand this correctly, as long as you work at 13.5 MHz and your signal includes pixels 9-710 you are OK.
(or in other words, active area at least 52 microseconds with the center, pixel 360-361, in the middle)

Which would make both Terratec devices compliant.

The SAA7113 (chip in grabster) lacks a scaler.
There are other devices based on this chip which will capture less than 720 pixels, but those pixels will either be 1/13.5 microseconds wide, and the remaining pixels are cropped OR there is rescaling done by the driver.

[Arachnotron]

I just found out:

at

http://www.itu.int/publications/index.html

You can download the ITU specifications. You normally have to pay for that BUT you can register and get 3 free downloads per year.

I only needed ITU-R BT.601-5 and BT.470-6. :)

[erratic]

Apparently der Karl's website and his document Capture-Karten und aspect-ratio für Dummies are no longer available. An English translation can be found on Arachnotron's website (http://www.arachnotron.nl/).

[Arachnotron]

Try this link:

http://forum.gleitz.info/attachment.php?attachmentid=66736

[erratic]

Yep, it's there. But Doom9's Capture Guide also mentions Karl's document and it still points to the old website, so one of the authors needs to update the guide.

[Arachnotron]

The capture guide is being revised right now and the new version will be released shortly.

[erratic]

I don't want to bother you too much, Arachnotron, but on your website (http://www.arachnotron.nl/) you also mention the document a few times, so you need to update your website as well. :)

[Arachnotron]

I know, I know....

Since the important bits will end up in the next capguide release anyway I intend to take it down after the new version of the guide is released. So I haven't bothered to make any improvements to it for a while.

[BaronVlad]

Hi there,

that is quite funny, I just came here to point the link Arachnotron did. So there is nothing more to say but have a nice evening and sorry for OT ;)