720x480 VS 640x480: What am I missing?

Question

720x480 VS 640x480: What am I missing?

Howdy forum!

I have a clip of captured DV at 720x480. ( http://www.banyots.com/images/dvclip.jpg )

I have a .mov file that's also 720x480. ( http://www.banyots.com/images/streamclip.jpg )
(originally an iPhoto exported slideshow, and run through MPEGStreamclip)

So why is it, that when using Final Cut Express 4, exporting the QT file, using iDVD 5.0.1 to make a DVD, that the DV clip produces a nice 720x480 DVD picture, but the other file gives me a 640x480 DVD picture, that is CLEARLY the 720 pixels smashed into 640?

I don't understand how two pieces of video, that as far I can tell, have the same size, and are producing different results. I'm losing my mind,

Dave

G5 Dual 2.0/2.5 Gig RAM/1000+GB HDs/DVD-RW, Mac OS X (10.4.11), FCE 4.0, iDVD 5.0.1, Quicktime 7.4.1

Posted on Feb 19, 2008 7:41 PM

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Answer 1

J Keller

Level 4

2,750 points

Feb 21, 2008 8:49 PM in response to David Banyots

Not sure why you're running the file through MPEG Streamclip, but perhaps you're also changing the destination file size.
John

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Answer 2

PT

Level 7

20,894 points

Feb 27, 2008 11:03 AM in response to David Banyots

I am not sure exactly why, but I can tell you that on a TV you have the equivalent to 720x480 "pixels" on the screen (not real pixels since NTSC TVs are analog). The 720 pixels are actually "rectangular" (again, analog so not real rectangles) pixels which are tall and narrow.
On a Computer, 720 NTSC TV "rectangular pixels" are about the same as 640 square computer pixels. In applications like iMovie (and I assume the Final Cut products) does the conversion "behind the scenes" from computer to TV sized resolution. So when you import DV formatted video, you see it on the screen as 640x480 but it is really 720x480 TV pixels that iMovie is working with. Likewise, say you add a 640x480 JPG to your project. iMovie will continue to show you the JPG as a 640x480 computer formatted JPG but under the hood it has converted it into 720x480 TV pixels.
So getting back to your problem, as I said, I don't know for sure if this is it or exactly how to fix it, but I am assuming there must be some sort of convert or no-convert depending on the format where a native DV format video is left alone while an MPEG video is assumed to need some sort of conversion? Although now that I give it further thought, you would think it would go the other way and take the 720 MPEG and make it 810 (trying to convert 720 "squares" into more rectangles).
?????
I don't know, but maybe something in the above will give you some ideas of what to look for. My guess is that it has something to do with the export to QT where the option to keep the resolution the same or whatever the setting is should be used for one but not the other.
To give you an example, I know if you export out of iMovie a DV clip to a QT file and let it leave the resolution the same (the default I believe) you get a stretched out movie that is 720x480 but because the computer has square pixels, the image is stretched which would look fine if viewed on a TV. For computer viewing you have to tell it to make the export 640x480 to make it look the same as it does in iMovie. As I said, in iMovie the clip is displayed 640 but really is 720. When exporting you want the exported version, for computer viewing, to reflect the displayed version, not the actual.
I am out of thoughts (finally!). Sorry for the long winded, possibly repetitive, stream of thought.
Best of luck,
Patrick

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