[mythtv-users] OT: 16:9 vs 4:3 signals

[Robert Denier]

David Farber wrote:

>Sorry for the off-topic post, but I expect that someone on this list has the technical knowledge to answer this question.
>
>How is the aspect ratio of a video signal negotiated between two video devices?  For example, let's say I have a DVD player capable of 480p output.  Am I correct is assuming that I would get a larger, higher resolution picture if I plugged this dvd player into a 17-inch 16:9 480p-capable tv/monitor than if I plugged the same dvd player into a 17-inh 4:3 4800-capable tv-monitor?
>  
>

Disclaimer:  I may be a little off here, but it should be basically correct.

First off 480 p describes the distinct number of lines in the image per 
frame.  An ordinary TV signal has (from memory) 525 lines but only half 
of them are drawn at a given time of which only 480 are visible.  This 
may not be exactly true, but essentially the 240 even number lines are 
drawn and then immediately after the 240 odd numbered lines are drawn.  
Thus you get essentially 59.97 fields per second for plain ntsc video.

I don't recall off hand what the frame rate is for 480p, although at a 
guess its probably 29.97 fps.  The difference here is all 480 lines are 
drawn at once leading to a smoother less distorted image.

Now to get back to your original question.  First off your dvd player is 
going to be playing some kind of mpeg 2 signal.  If it is formated such 
that the output is true 16:9 widescreen, then yes you will definitely 
get a better picture on the 16:9 monitor.  If on the other hand, as with 
the majority of dvd's it is just sending out material thats 4:3 then  
your not going to gain anything with the different display. 

There are also dvd's that encode 16:9 aspect ratio material in 4:3 
format on the dvd, thus yielding top and bottem bars.  This is not 
sharper than a dvd recorded  in 4:3, but you do see the original 
structure of the film rather than losing some of it in the pan and scan 
process.

Afaik the dvd format is fixed at 720x480 resolution for NTSC, but I 
could be wrong since I haven't kept up on the high end details.  I 
believe some movies do some kind of anamorphic widescreen such that the 
entire frame is digitalized into a 720x480 grid.  This allows one to use 
the entire resolution available on a dvd to display the movie back in 
its original (or close to it) aspect ratio on the widescreen monitor.

Would this kind of movie have more detail than an ordinary movie made 
for a 4:3 monitor?  Nope, its just that the details are in different 
places.  I think there is some kind of hdtv dvd standard coming out or 
maybe its already out which would obviously make the widescreen monitor 
more attractive and eliminate these problems.  Additionally there are 
hdtv services available from direct tv and dish network that also do not 
have these limitations.  There are also hdtv television services of the 
broadcast networks in some areas.

Basically the conclusions are
1) 480p is just the format it is presented.  Yes this is preferable, and 
yes if both monitors support it, you will get similar quality.  If one 
monitor only supports 480i then the other will look better, but only on 
material that actually is 480p.
2) Beyond that you want to match the monitor to the aspect ratio of the 
source material, when possible.

Note that I don't keep up on a lot of the high tech toys I can't afford 
so my info may be a bit out of date.

>Can the dvd player detect the presence of a 16:9 tv versus a 4:3 tv?  Or is the 16:9 tv set scaing the 4:3 picture?
>  
>
Well if there was any detection it would probably be the tv that was 
doing it.  I'm not sure since I don't own one.


-Robert Denier

>Thanks for the info,
>david
>
>
>
>--
>David Farber
>dfarber at numenor.com
>  
>
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