DVD aspect vs TV aspect

[Yirkin]

It just occured to me while trying to resize a source file that my TV is 1.3:1 aspect where as the DVD format is 1.5:1 (720x480). When I make DVD size mpgs, they end up looking stretched when I view them on my PC because a 640x480 file will stretch to 720x480. But, for some reason when I view them on my TV, they appear to squeeze back into a 1.3:1 aspect ratio. Am I on the right track? Is that what happens when I view a DVD on my television? Why did they choose 720x480 as the resolution for DVD-Video?

Are there any 1.5:1 aspect ratio TVs? I thought the choices were 1.3:1(4x3) or 1.78:1(16x9).

Thanks for the help,

Howard

[flaninacupboard]

the physical ratio between pixels is 1.5:1, but the actual aspect ratio of the material (i.e. the ratio at which when displayed it is correct) is 1.33:1 (normal TV.) the same is true for "widescreen enhanced 16:9" movies. the physical pixels are still 1.5:1, but the image they make up is 1.77:1 (widescreen)
why did they choose 720X480? well the 480 is fairly logical, that's the active number of lines in 4.43MHZ NTSC, (TV standard) and also happens to be as you pointed out VGA compatible. as for 720, who really knows. VCD was 352X240, so presumably they wanted double, but didn't like 704 (for whatever reason.)
It's more likely that they knew anamorhpic DVD would exist, and that DVD would fall in line with DV resolution, so 720 would be useful. i suggest a google search on this one.....

[Yirkin]

Thanks for responding.

If I take a 640x480(1.3:1) video on my computer say from a TV show and encode it into DVD format, would the width be stretched from 640 to 720? The height is already 480 so therefor would the image be stretched horazontally?

If I use TMPGEnc and choose Full Screen (Keep Aspect Ratio), I don't remember seeing it create big black bars on the left and right sides to account for the difference between 640 and 720 pixels. Is it stretching the video when encoding the DVD then squishing it back to 1.3:1 when I play it on my TV?

I'm just not sure why they do that rather then making the DVD-Video default to a standard TV size unless they picked a middle ground between the 4:3 screen and the 16:9 screen.

Howard

[Faceman101]

I've wondered myself why DVD and DV is 720 instead of 640. As far as your situation, encode your 640x480 footage as 720x480 full screen. Without any black bars. Your player will resize accordingly.

[Yirkin]

Thanks, that is what I was wondering.

Do set top DVD players resize the video from 720x480 back into the correct aspect ratio for the TV screen?

How about Software DVD players on the PC? Does the 640 that was stretched into 720 get squeezed back to the correct aspect ratio there too?

Howard

[flaninacupboard]

Yirkin, a television is not like a PC monitor, it doesn't really have a set "resolution", at least not in the way a monitor has a "resolution" of 1024X768 or 800X600. if you think about a line on a television, it doesn;t matter if you feed it with 30 pixels or 3000, a line is a line. i could make an MPEG that was 4096X480, and played into a TV (ok, i probably couldn;t do that, but for the sake of argument...) it would still just turn those 4096 pixels into a line. similarly a VCD has only 352 pixels across, but you still see a line.
Software DVD players don't always use the correct aspect ratio. this mean with NTSC material you may get small black bars top and bottom and with PAL you get black bars on the left and right. this varies from player to player, but i use powerDVD and it seems to do a good job.

i would assume the reason 720 was picked is yes because it's a halfway ground from 1.33 and 1.77.

[FulciLives]

I've converted some DivX files that were 640x480 using TMPGEnc and the resulting mpeg2 file of course is 720x480 and it looks fine to me. I think the difference here (although I'm not sure) is that DivX uses square pixels and DVD does not. That's the "story" I heard. So 640x480 is standard full screen size for DivX but for DVD it is 720x480 ...

I guess the point is ... don't worry about it! I've seen no real noticeable degradation in the picture when going from 640x480 DivX to 720x480 DVD and this includes NO aspect ratio problems.

Maybe someone else could get more technical about it?

- John "FulciLives" Coleman

[Yirkin]

Thanks for responding. It was very confusing to me how 640x480 and 720x480 can both maintain the same aspect ratio.

I was confused because when I open the mpg file in Media Player, it gets resized up to 720x540 automatically, something I didn't realize before. I guess that Media Player, and most likely other software DVD players, automatically make an adjustment in aspect ratio assuming the image was stretched out to 1.5:1 when it was encoded.

When I opened the mpg file in an editing program, it maintained its original measurements and I could see how much it was stretched.

Now if only I could figure out the difference in TMPEGEnc between Full Screen (Keep Aspect Ratio) and Full Screen (Keep Aspect Ratio 2).

Howard

[FulciLives]

Now if only I could figure out the difference in TMPEGEnc between Full Screen (Keep Aspect Ratio) and Full Screen (Keep Aspect Ratio 2).

I usually use FULL SCREEN (KEEP ASPECT RATIO 2) because it often puts a small amount of black on the sides and I figure this helps with overscan on a TV screen. Sometimes I notice no difference what-so-ever between the two (no black on the sides either way) so who know!

- John "FulciLives" Coleman