[mythtv-users] Resolution

DBakker at arrayasolutions.com DBakker at arrayasolutions.com
Wed Dec 3 17:02:20 EST 2003


Great info in this thread.

Does anyone know what a DirecTV receiver output resolution is (SVideo)?

-David
 



"Boyd II, Willy" <wboyd at fulbright.com> 
Sent by: mythtv-users-bounces at mythtv.org
12/03/2003 04:19 PM
Please respond to
Discussion about mythtv <mythtv-users at mythtv.org>


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Subject
RE: [mythtv-users] Resolution







>-----Original Message-----
>From: James L. Paul [mailto:james at mauibay.net] 
>Sent: Wednesday, December 03, 2003 3:08 PM
>To: papenfuss at vt.edu; Discussion about mythtv; 
>papenfuss at juneau.me.vt.edu
>Subject: Re: [mythtv-users] Resolution
>
>
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>On Wednesday 03 December 2003 10:30, papenfuss at juneau.me.vt.edu wrote:
>> On Wed, 3 Dec 2003,  James L. Paul wrote:
>> > > SO, with this in mind, take a few data points.  NTSC VHS has 240 
>> > > lines. Formatted at 4:3, this translates into 480 
>vertical pixels 
>> > > (NTSC viewable scan lines), and horizonally (240 * 4/3) = 320. 
>> > > So, to capture VHS-quality video, you need a capture 
>resolution of 
>> > > 320x480... 1/2 D1 is close at 352x480.  To capture high-quality 
>> > > broadcast at 330 lines, (330 * 4/3) = 440... SVCD is close at 
>> > > 480x480.  Capturing any more than that wastes encoding time, 
>> > > space, encoding quality, etc.
>> >
>> > This is a much better description than mine. As I remember 
>it though 
>> > there was some effect caused by interlacing, real-world signal 
>> > loss/distortion and quality of video tape that made VHS generally 
>> > considered 352x240, although I can see now the 352 is obviously 
>> > inflated. (Perhaps that explains why all the VCDs I made from my 
>> > DirecTV looked better than VHS from the same source.) I think it's 
>> > the way the interlaced frames are helically laid down on the tape, 
>> > there is significant bleed on VHS, but SVHS used denser tape and 
>> > probably smaller heads.
>>
>>               The 352 is not all that inflated.  At the rated 240 
lines, that 
>> equates to 320 pixels horizonally.
>>
>> > So the way I understood it, although all NTSC video has 525 lines, 
>> > about 480 of them viewable, the analog storage and reproduction of 
>> > VHS tape doesn't accurately retain the resolution of all them, and 
>> > results in about half. It's as if the interlaced video 
>interpolates 
>> > itself unnecessarily. This may be totally wrong. I've never 
>> > questioned it though since seems to match my experience.
>>
>>               I thought about that, and that's actually what I was 
>thinkign when I 
>> was searching for the definition of resolution.  I'd be tempted to 
>> believe it, but remember that two adjacent lines on the 
>screen are put 
>> on the tape 1/30th of a second later (well, 1/29.97th, but who's 
>> counting!).  If they were to bleed into each other, they 
>would soften 
>> the whole thing up so that you couldn't distinguish 
>individual fields. 
>> Recording from VHS tape at 480 vertical pixels definately shows a 
>> clearly interlaced picture.
>>
>>               I'm not saying that there's not bleed-through between 
>adjacent scans 
>> on the tape, but it's not much of a factor.
>
>I wasn't talking about bleed that way, perhaps bleed is a bad 
>word choice. Of 
>course you get properly interlaced video. I meant that the 
>nature of storing 
>analog signals on magnetic tape so closely together and the process of 
>writing/reading them with a head that isn't fine enough to 
>completely avoid 
>the adjacent signal of the interlaced fields on the tape.
>
>The signal on the tape has a strong center and drops off 
>sharply the farther 
>you get from the center, and the interlaced field signals are written 
>alternately adjacent to each other. It was the signals being 
>so close to each 
>other on the tape that I meant by bleed. As each field is laid 
>down on the 
>tape, the recording head isn't far enough away from the 
>previous field to 
>totally avoid affecting it, and the same thing happens when 
>reading, the read 
>head gets the center of the field but isn't totally unaffected 
>by the two 
>interlaced fields next to it. This is all part of what gives 
>VHS the quality 
>it has. (Or doesn't have, as the case may be.)
>
>Disclaimer: I don't have any references to back this up, I 
>don't remember 
>where I learned this, and I may be full of hot air on this one.
>
>As for beelding into each other such that they soften up or 
>being unable to 
>distinguish individual fields, this does happen, and it's why 
>VHS has a shelf 
>life. I have tapes from 20 years ago that are unplayable now, 
>and others that 
>get worse each year when I pop them in to check. (I do this 
>out of curiosity, 
>I started archiving my VHS to VCD in 1996, and switched to CVD 
>in 2001, and 
>now use DVD. Every year of so I sit down and play tapes I 
>"rescued" to see 
>how long they actually lasted. :)

Just out of curiousity, do you use a certain brand of cd-r or dvd-r discs
in order to maximize shelf life for those archives?  (I'm merely
piggy-backing off your archival
research :-)

- Willy
>
>> -Cory
>>
>>  --
>> 
>***************************************************************
>**********
>> * The prime directive of Linux:  
>                *
>> *             - learn what you don't know,  
>                *
>> *             - teach what you do.  
>                *
>> *             (Just my 20 
>USm$)           *
>> 
>**********************************************************************
>> ***
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