4:3, or not 4:3 ?

[meirionwyllt]

Why do they say DVD resolution (720x576) is 4:3 when in fact it isn't?
720x576 has a ratio of 1.25 but 4:3 has a ratio of 1.33 (recurring). A DVD
would need to be 768x576 to be truly 4:3. Does this mean that if I convert
videos from my digicam (truly 4:3) to DVD quality then the picture would be
slightly squashed? Either that or having to remove a thin strip either side
of my videos for it to fit?

[benbryant]

Please go the link to learn more about "Aspect Ratios"

http://www.doom9.org/index.html?/aspectratios.htm

Regards

[blutach]

See here for a full explanation.

Regards

[meirionwyllt]

Thank you both for your replies. Unfortunately neither webpage encountered my question, they were both concerned with watching 16:9 films on 4:3 TVs, or vice versa, which I knew anyway. Besides, with this certain issue it's only 4:3 that I'm interested in. However, on the page that blutach posted, I did find a link to this page:

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

This page at least raises the issue of my question, but I still had some doubts after reading.

Maybe I didn't make myself clear the first time. What I want to know is why is 720x576 referred to as 4:3 (1.33) when in fact it is not quite 1.33. By doing the calculation you will find that 720x576 is in fact 1.25.

Part B of my question is thus, if I want to convert a video shot from a digicam that is 320x240 (which is a true 4:3, also 1.33), would I...

a) Convert the resolution to 720x576 to obey the DVD standard but have to stretch it vertically to make it fit (since 720x576, as mentioned above, is not truly 1.33), or...

b) Convert it to 720x540 (keeping it truly 1.33), then giving it mattes above and below with a height of 18 pixels each, to obey the DVD standard. The next question here would have to be, which program is the best for adding mattes of user-defined heights. ?

[drfsupercenter]

The same happens with NTSC... 720/480 is not 1.33 either. I think the DVD player stretches the image to fit 4x3, as when I play a VOB file in Windows Media Player or other player, it is not 4x3 and looks stretched. On Nero ShowTime it looks fine.

The world may never know.

[meirionwyllt]

Right, so if I stretch my video to DVD standard resolution (rather than putting in mattes up and below), then are you saying the TV will stretch it back on playback, thus returning the video to its previous aspect ratio??

[blutach]

The issue that you face is overscan - read that link I gave you again. If you are 720 x 576, it only displays 540 lines due to overscan. Keep you images at 720 x something and the overscan will take care of it.

Regards

[meirionwyllt]

So are you saying that it's better to encode to 720x540 (truly 1.33) and let the DVD player / TV do the rest, than encode to 720x576 straight away?

[blutach]

To be on standard, you need to encode to 720 x 576

Regards