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Old 1st March 2002, 13:40   #1  |  Link
Wilbert
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aspect ratio after capturing

Probably a dumb question. Suppose you are capturing from a normal tv (let's say to 704x576), what will be the aspect ratio of your captured movie. Is it 4:3 or 1:1?

I always assumed it is 4:3, but I'm not sure about that.
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Old 1st March 2002, 13:55   #2  |  Link
Kedirekin
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Interesting question.

Unfortunately, I don't think you can make such comparisons. TV's are truly analog devices (at least, in the horizontal direction). It's really just three electron guns varying their relative intensity over time in a smooth, progressive, non-discrete (i.e. non-digital) way. It's somewhat akin to asking 'what is the resolution of a wave in a pond?'.

I think you can talk about resolution in the vertical direction, because scan lines are pretty discrete (525/625, I think, but only 480/576 are visible).

For horizontal, I think the best you can do is talk about effective resolution. And when you do that, I think the 'TV' aspect is neither 4:3 or 1:1. I think the DVD resolution of 720x480/576 (1.5:1(ntsc)/1.25:1(pal)) is probably much closer to the 'real' TV aspect.
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Old 1st March 2002, 14:17   #3  |  Link
Wilbert
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Ok, I know that a tv has no aspect ratio. It has 625 lines for PAL, etc. Let me give an example:

I made a capture to 704x576 from a normal tv. I resized it with VDub to 480x576 without adding black borders and without cropping. I use TMPEnc to encode it to SVCD with the following settings:

video --> in the video stream settings (you can't choose the first two):
480 x 576
4:3 display
interlace

advanced --> in the video source settings:
non-interlace (progressive)
4:3 display (*)
full screen (keep aspect ratio)

Question: what should I choose here (*). Should I choose "1:1 vga" or "4:3 display" or probably "4:3 625 PAL" and why? If I choose the latter, that is 4:3 625 PAL, and I watch it full screen on my PC the AR is not correct (picture is squeezed a bit). I don't know what happens if you watch this SVCD (with "4:3 625 PAL") on your TV.

If I choose "4:3 display" it won't play correct on my tv (but it plays correct on my PC), I've to stretch the image vertically.
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Old 1st March 2002, 15:35   #4  |  Link
Kedirekin
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I always hated the aspect ratio 'features' of TMpg. It hides a lot of the resizing and adding borders that it does behind these aspect settings. Some people love it, but I hate it.

I'm pretty sure the on the first tab (is it called just 'video'?) you have to set it to 4:3 and 480x576. I don't think you have any choice there. If you're source is progressive (no combing), you should probably use progressive rather than interlaced. The compressor should be more efficient and produce better results when set to progressive. If there is combing, you probably want to stick with interlaced.

As for the advanced tab, I can't give too much advice, because I'm not that experienced with it. For a 4:3->4:3 encode, I think you're safe choosing 4:3 625. On the other hand, you may have to choose 1:1. Probably better if you could ask someone who has more experience, or failing that, encode some test chapter to gain the experience yourself.
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Old 1st March 2002, 15:42   #5  |  Link
Kedirekin
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Oh, BTW: I remember another setting on the advanced tab that effects all this stuff. I don't remember the name, but it had choices like center, preserve aspect ratio, custom. I recall it effected all the resizing and add borders stuff too.

As for being wrong when you watch it on your PC, you should sort-of expect it to be wrong in many cases. That's because the 480x576 resolution is definately not 4:3. To display correctly, it really needs to be resized on playback to 640x480 (or maybe 768x576) to look right. Some playback tools (WinDVD) will do this, others (Media Player) often will not.
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Old 4th March 2002, 12:12   #6  |  Link
Wilbert
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Please have a look at the thread

"Aspect Ratio problems when playing on home DVD player"

in

"SVCD encoding & authoring"

for further info.
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Old 4th March 2002, 18:42   #7  |  Link
Scuba
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I think that you are mixing Picture aspect ratio and Pixel aspect ratio.
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Old 10th March 2002, 09:08   #8  |  Link
chemmajik
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Age old question if a tv out device defaults to 640x480, finding the best final video scaled size to look best, to keep the file sizes as small as possible, but keep the best quality before it drops.
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