resolution / pixel aspect ratio confusion

[greg0ry]

horribly confused about resolutions/aspect ratios
-working with original video @ 640x480 and 1.0(square) pixel aspect ratio(a motion jpeg taken with my primary still camera)
-video will be put on a dvd @ 720x480 and 0.9091(ntsc dv) pixel aspect ratio(from what i gather this is what dvds have to be in th u.s?)

ok so, 640x480 with square pixels when converted to ntsc 0.9091 pixel ratio should give me 582x480 right? 640 x 0.9091 = 582

what i was thinking is that the rendered video would be centered horizontally with black bars at the sides(because 582 is less than 720), however when i check the properties of the rendered file in windows media player, it says 720x480 4:3 and the video fills the entire frame, this in itself confuses me, i don't understand how and why this is

also the rendered video(720x480) is bigger both horizontally and vertically than the original video(640x480), i suppose i understand why it's bigger horizontally, but why vertically as well if both are 480

i'm missing something big here, and any help would be greatly appreciated

[mats.hogberg]

Just resize to 720x480, and set the DAR to 4:3 and you're home free.

/Mats

[edDV]

horribly confused about resolutions/aspect ratios
-working with original video @ 640x480 and 1.0(square) pixel aspect ratio(a motion jpeg taken with my primary still camera)
-video will be put on a dvd @ 720x480 and 0.9091(ntsc dv) pixel aspect ratio(from what i gather this is what dvds have to be in th u.s?)

ok so, 640x480 with square pixels when converted to ntsc 0.9091 pixel ratio should give me 582x480 right? 640 x 0.9091 = 582

what i was thinking is that the rendered video would be centered horizontally with black bars at the sides(because 582 is less than 720), however when i check the properties of the rendered file in windows media player, it says 720x480 4:3 and the video fills the entire frame, this in itself confuses me, i don't understand how and why this is

also the rendered video(720x480) is bigger both horizontally and vertically than the original video(640x480), i suppose i understand why it's bigger horizontally, but why vertically as well if both are 480

i'm missing something big here, and any help would be greatly appreciated

Are you sure you want to fully understand this?

A "good enough" fit would use a 720/640 or 1.125 horizontal scaling and you are done. Dividing 640 H by 0.9091 gets you to 704.

A technically correct scaling would use a non-intuitive 4320/4739 = 0.91158 PAR. If applied to 640x480 you get 702x480 with black side bars. 480 is considered a cropped format since actual NTSC was 486 lines. If you were to enlarge your 640x480 to NTSC correct 648x486, then the 0.91158 PAR would get you 710.85x480 still with black side bars but also with 3 lines cropped top and bottom.

ATSC/DVB digital broadcasting use 704x480. Analog (480 line) to digital conversions result in 702 horizontal pixels with one pixel side bars or 704 pixels with some top and bottom crop. Analog (486 line) to 704x480 can result in 3 pixel side cropping and 3 line top and bottom cropping unless resized.

Most analog TV captures to 720x480 will have 8 or 9 pixel black side bars left and right. (see below)

Details here
http://lipas.uwasa.fi/~f76998/video/conversion/

Typical tuner capture to 720x480


Here is a more technically correct capture to 720x480 (using canopus ADVC-100).



A more "correct" conversion back to square pixel 640x480 would require first a side crop to 704x480 then a 0.9091 horizontal scale.