Progressive Scan

[Jeff Agnew]

It is the progressive scan (repeating every other line) that cause computers to go nuts. Since they are NOT designed for that; it was designed for TV sets.

Just in the interest of clarity, and with due respect for Carl, actually the opposite is true. An interlaced display is the type that alternates scan lines and is what all standard analog US television sets use. The NTSC system employs 525 lines, interlaced. So you're actually only seeing half of them at one time. In today's digital parlance you could think of it as 525i. Some digital sets offer an interlaced setting (such as 1080i) but most HD these days is progressive.

All modern computer displays natively use progressive scan. So if you're having YouTube playback problems, that's not the issue. It's almost certainly a bandwidth problem, so lowering from 720/480p to 360p makes things better by requiring less information to be sent through your net connection.

Please excuse this detour from the topic of this thread. We now return you to your regular programming.

[C Dixon]

It is the progressive scan (repeating every other line) that cause computers to go nuts. Since they are NOT designed for that; it was designed for TV sets.

Just in the interest of clarity, and with due respect for Carl, actually the opposite is true. An interlaced display is the type that alternates scan lines and is what all standard analog US television sets use. The NTSC system employs 525 lines, interlaced. So you're actually only seeing half of them at one time. In today's digital parlance you could think of it as 525i. Some digital sets offer an interlaced setting (such as 1080i) but most HD these days is progressive.

All modern computer displays natively use progressive scan. So if you're having YouTube playback problems, that's not the issue. It's almost certainly a bandwidth problem, so lowering from 720/480p to 360p makes things better by requiring less information to be sent through your net connection.

Please excuse this detour from the topic of this thread. We now return you to your regular programming.

Ok, I should have been more succinct.

Interlaced scanning repeats NO lines. Progressive scanning has ALL lines to fit within the "HD" protocol.

Notice I said it "repeats" every "other" line. Not skips ever other line as Interlaced scanning does. This is why ALL High Definition "ready" TV's cause the "blacks" in the scene to look TOO dark, when receiving "standard" (interlaced)* TV broadcasts. I hate it!

Same goes for the whites when displaying "standard definition" TV broadcasts, IE; TOO brite. However when these same TV's are displaying "HD" TV broadcasts, they are absolutely gorgeous.

The FCC allowed this, because "standard" (interlaced) broadcasts were, and are, being phased out, so it was just a temporary malady.

Here is the difference graphically:

[tab]

(NTSC Standard) (ATSC HD)

Broadcast Broadcast

HD Ready TV HD ready/HDTV

Prog Int Prog Int

Line 1 1 1 1
| 1 241 2 541
Line 2 2 3 2
| 2 242 4 542
Line 3 3 5 3
| 3 243 6 543
Line 4 4 7 4
| 4 244 8 544
| | | | |
| | | | |
| | | | |
Line 480 240 | |
Line 480P 480I | |
| | |
| | |
| | |
Line-----------------1079 540
Line-----------------1080P 1080I


[/tab]

c.

*On HI Def TV's, this problem does not cause the above abberation, because these TV's had circuity to accomadate either P or I; albeit Progressive TV's seem to be a bit sharper. They really aren't, but they have NO semblance of "flicker" so the human eye/brain perceives the very slight flicker as less sharp.

In fact the very reason that the original NTSC standard required "interlaced" TV's (1946), was to decrease flicker, while not totally eliminating it. This due to the "retentivity" (images in the eye's retina decaying slowly), being exceeded.

Resulting in flicker.

This is now history, because ALL TV's in the future will not have a nuance of a flicker. Praise Jesus!

[Jeff Agnew]

Carl,

Sorry, I misread and thought your original comment confused interlaced and progressive scanning. Apologies for my simplistic reply but I wasn't sure of your level of knowledge on the subject, which is obviously high.

I still don't understand why you said progressive scanning content causes computers to "go nuts" while playing back YouTube videos. What are the symptoms you see?

[C Dixon]

Carl,

Sorry, I misread and thought your original comment confused interlaced and progressive scanning. Apologies for my simplistic reply but I wasn't sure of your level of knowledge on the subject, which is obviously high.

I still don't understand why you said progressive scanning content causes computers to "go nuts" while playing back YouTube videos. What are the symptoms you see?

Very good question Jeff.

Ok, when the NSTC in 1946 determined how to fit video, audio and syncronizing signals into the given broadcasting "spectrum", it carried with it MANY problems, that we STILL live with in ANY Analog TV set. They KNEW this, but it was the best they could come up with, in yesteryear's technology.

However, beginning with the latest technology, "High Definition TV standards" solved those maladies.

BUT....to keep from making ALL analog TV signals from instantly becoming UNusable, they built in a temporary remedy that would phase out over time and be uneeded.

Computers being built around the NEW standard do not understand some of the above. There was NO need to, they thought! Because it worked on an entirely different protocol. And it was a self contained medium. They thought!

But along comes MULTIMEDIA (Analog video and audio based on the old NTSC protocol), and you send an analog signal (like Utube videos and DVD's), you cause a computer to get confused.

Such is the case with Progressive scans versus the analog derived Interlaced scanning used on all TV's until "HD ready TV" came along; quickly followed by HD TV's..

The higher the resolution using progressive scanning when trying to display something that was recorded in Interlaced scanning (Say 460P vs 360P) the more your computer is apt to get confused.

Thus my,

"It drives computers nuts!"

Thanks for understanding and double thanks for your question dear brother,

c.

[Jeff Agnew]

Carl,

Many thanks for your explanation. I do understand the technology and broadcast standards -- I just don't understand what type of problems you encountered playing videos on your computer.

But to avoid further topic drift, if you don't mind I'll send you an e-mail and we can avoid boring non-SMPTE folks with the trivia.

I think we may just have a semantic misunderstanding.

[C Dixon]

Amen Jeff,