capture resolutions

[Woodlake]

I'm trying to get my head around aspect ratio's and just have a question:

This was a quote from an old thread by Arachnotron:
"Suppose it (your capture card) is 52.15µs. In that case, cap 704x576, and add 16 black pixels to get 720x576 (or let your MPG2 encoder do it for you) and the AR of the DVD is correct."

I cant work out why you would pad the video.
If I capture at 704x576 (PAL) (which has an active picture area of 702x576) and take the same capture, and pad it out to 720x576 (which has the SAME active area AND AR of 128/117) - wouldn't both of these display exactly the same on a tv?

If this is the case I assume that the only reason you would capture at a higher resolution would be if your capture card captures higher than 52.15 µs?


Woodlake

[Arachnotron]

I cant work out why you would pad the video.
If I capture at 704x576 (PAL) (which has an active picture area of 702x576) and take the same capture, and pad it out to 720x576 (which has the SAME active area AND AR of 128/117) - wouldn't both of these display exactly the same on a tv?

Note that the above is only valid when producing DVD's. Both 704x576 and 720x576 are valid DVD resolutions. If you did not pad, and made a 704x576 MPEG2 file out of it for DVD or pad to 720x576 and turn that into a DVD, the result on TV would be the same and have the same active area.

The catch however is in what mpeg2 encoders do when you feed them with a 704x576 source. TMPGENC for instance will, when you use the default PAL template, resize it to 720x576 (at least the last version I used did). This will mess up the AR. You can disable this and tell it to padd (center) instead, but you have to override the defaults for that.

Since I don't know which encoders people use and what settings they have (and because I am lazy and don't want to explain all that :) ) I tend to advise people to pad to 720x576. 720x576 files will be left alone by all encoders and always come out right.

[Woodlake]

Arachnotron,
Thank you for your (very quick!) reply. I use CCE to encode at 704x576 and I wasn't sure if I was missing something obvious :D

Woodlake

PS I definetely dont think your lazy - I have ready many many of your posts and you have been a huge help to me in the past - thanks again for taking the time to reply.