688x480 captures & resizing

[Zutton]

Hi,

I've spent a good deal of time reading through all the great posts here, and think I've got everything down 90+%, but I have a couple of follow-up questions I was hoping to please get some assistance with.

I currently have an Asus TVTUNERCARD 880, and using Arachnotron's awesome site here (http://www.arachnotron.nl/videocap/site/capture_area2.html) I have determined that my card captures 688 NTSC horizontal [50.96ms, CX23880 based card, ASUSTeK WDM 2.0.67.0]. I have been capping using VirtualVCR at 688x480 to avoid any horizontal scaling of my caps.

I've also looked over trevlac's site here (http://trevlac.us/preface.htm). Based on info on this site, I have determined the following:

To cap for DVD authoring, I cap at 688x480 and add borders of 16 left/right to reach 720x480.

To cap for SVCD, I can cap at 458X480 and add borders of 11 left/right to reach 480x480 (458=50.96ms * 9MHz SVCD sample rate).

Here are my questions:

1) Looking for validation that the above statements re: DVD/SVCD sizes and borders are correct for my card.

2) If I have a 688X480 cap that I want to convert to SVCD, I'm assuming I should resize to 458X480 and add borders of 11 left/right. This is based on the fact that 458X480 would be the proper "RAW" capture size to use, and thus should be the target resize for my 688X480 cap. Is this correct?

3) If #2 is correct, could I trouble someone for the specific math? Still a bit confused on the PAR stuff, and most info I've seen uses a 720x480 size for examples, so I'm having issues translating this to 688x480.

Thanks in advance,

-Zutton

[trevlac]

I'm glad you found the info useful. I think you are on the right track.

Originally posted by Zutton
1) Looking for validation that the above statements re: DVD/SVCD sizes and borders are correct for my card.

You are correct. The only comment I'd make is, 704 is valid for DVD, so that's a better size for you to pad to.

2) If I have a 688X480 cap that I want to convert to SVCD, I'm assuming I should resize to 458X480 and add borders of 11 left/right. This is based on the fact that 458X480 would be the proper "RAW" capture size to use, and thus should be the target resize for my 688X480 cap. Is this correct?

You are completely correct. Do know that with a post cap resize, you will loose more resolution than you might have to. This is under current debate, and is definately dependant upon your drivers.

3) If #2 is correct, could I trouble someone for the specific math? Still a bit confused on the PAR stuff, and most info I've seen uses a 720x480 size for examples, so I'm having issues translating this to 688x480.


To understand PAR you should simply think shrink/stretch vs crop/pad. The 1st changes PAR, the 2nd does not. When your card captures 688 pixels these are a cropped version of the 720 pixels everyone talks about. They have the same PAR. AKA 720 = the full 53.33 microsecond line. Your card crops the line to 50.96 microseconds. Changeing from DVD to SVCD does change the PAR (shrink the picture).

The math? Well I guess it is DVDPar * 2/3 = SVCDPar. Just like 13.5MHz * 2/3 = 9MHz and 720 * 2/3 = 480 and 688 * 2/3 = 458.

I think the confusing thing is that 704 (DVD) is a cropped version of 720 (DVD) and 352 (1/2DVD) is 1/2 of the cropped version but 480 (SVCD) is 2/3 of the non-cropped version.

I think PAR is a bit artificial. Most people seem to think in terms of the entire picture, not the pixels in the picture. PAR only really is useful for TV->PC conversions. If you have TV source and are going to watch thru a TV standard (like svcd,vcd,dvd) then it is easier to forget PAR and just think of how the standards relate to each other.

Hope this helps... I'm affraid I've begun to rant. :p

Edit I wanted to make it clear, I no longer agree with the statements about 'capture at the largest size possible'. It depends upon what your card driver does and/or how you resize after capture.

In the end, if done correctly, I believe VHS can always be done at 352, and most BCast can be done at 480. Doing it correctly is a bit of a challange. You need to really know your equipment. :D

[Zutton]

Originally posted by trevlac
You are correct. The only comment I'd make is, 704 is valid for DVD, so that's a better size for you to pad to. Forgot about 704, and that does make more sense, thanks!
The math? Well I guess it is DVDPar * 2/3 = SVCDPar. Just like 13.5MHz * 2/3 = 9MHz and 720 * 2/3 = 480 and 688 * 2/3 = 458.Thanks again - that's why I was looking for [Seems so obvious now :) ]

I wanted to make it clear, I no longer agree with the statements about 'capture at the largest size possible'. It depends upon what your card driver does and/or how you resize after capture.

In the end, if done correctly, I believe VHS can always be done at 352, and most BCast can be done at 480. Doing it correctly is a bit of a challange. You need to really know your equipment. :D So VHS in my case means cap at 344X480 and pad 4 left/right, correct?

Also, I'll have to read the thread where the 'capture at the largest size possible' discussion is going on. I'd like to learn more.

Thanks again for all the assistance,

-Zutton

[Zutton]

trevlac,

Just read a bunch of the posts in the which capture size to use for VHS caps thread. Most of it is over my head, I'll have to re-read it a few times.

One thing though that got my attention was your comment that the max resolution of the BT chips is 640x480. Yet, on your preface website using the lowest capture width of the listed BT drivers yields a capture window of 688. This seems to conflict with the 640 number. Was wondering what I am missing.

Thanks in advance,

-Zutton

[trevlac]

"So VHS in my case means cap at 344X480 and pad 4 left/right, correct?"

Well, if you have a BT/CX chip, I wouldn't do that. Anything less than 368 will mess up the vertical resolution. Unfortunately, the debate over this continues, and I have not worked out how to do this in a clear fashion.

As far as bt limited to 640x480, that's resolution, which is not the same as frame size. 688 is a good frame size for you. It gets the aspect correct. Resolution is a whole nother story ... :D

[Arachnotron]

640x480. Yet, on your preface website using the lowest capture width of the listed BT drivers yields a capture window of 688

Look at it this way: going higher than 640 won't give you more detail. But capping at 688 makes it easier to create DVD's, since you don't need to re-size, only add a few black pixels.

[trevlac]

@Zutton

Originally posted by Arachnotron
Look at it this way: going higher than 640 won't give you more detail. But capping at 688 makes it easier to create DVD's, since you don't need to re-size, only add a few black pixels.

Bingo! I couldn't have said it better myself. :) And you wont even see those Black pixels on your TV.

[Zutton]

Arachnotron & trevlac-

Thanks, that all makes sense now!

I plan on using trevlac's "Resolution" test this weekend and will share results. Since my Asus 880 is CX23881 based, I'm guessing I will experience the reduced vertical resolution at 344x480. Nevertheless, I will confirm for sure and post in the other thread.

-Zutton