720x480 vs 640x480

Although I have been editing on FCP for over 10 years now, here's a queation I never thought of asking ... until now. Why does FCP edit in 720x480 instead of 640x480?

Short answer? Because 720x480 is television and 640x480 is not.

Slightly longer answer: The CCIR-601 spec that first codified digital television specified 720 luma samples per scan line. These samples are not square; if you convert them into pixels, the pixels have to be little rectangles. Computer screens these days have square pixels. To keep the aspect ratio of the picture correct, computers convert the 720 luma samples and 720 chroma samples into 640 R, G and B samples. You can change the number of samples per scan line by simple interpolation, but you can't change the number of scan lines without radically effing up the picture structure.

And I'm even fairly sure I'm right about all that. I'm doing it from memory. Details not guaranteed to be, y'know, entirely true. But that's the gist of it.

Thank you for your response, but...

We tried going to Sound Track Pro but we do not know how to use the software program.
Before you answer perhaps we can give you the specs that were returned to us from FotoKem.

We submitted our 16mm film to be transfered to a digi beta (4.3) full frame. What was returned to us was a video track with the following specs: 720x486; 29.97; 10bit uncompressed; 4:2:2.

We also submitted 1/4" audio tape which was transferred in ProTools at FotoKem.We received back an audio mono track 01. wave; 140.6 K/sec; 48.0 KHz; 24 bit integer.

We know the timeline settings have to match the 720x486 format, but when we try to change the settings we get the following message: "Codec not found. You may be using a compression type without the corresponding hardware card." Help. This is really Greek.

Uh, I think you posted in the wrong thread here Armenian...

There are two aspect ratios in play the picture aspect ratio (the ratio of the screen)
verses the pixel aspect ratio.

Let's play some algebra
For 4:3 old-school TV the picture aspect ratio (ar) is 1.33333
For Computer screens the picture aspect is still 1.3333
For rectangular pixels on tv the pixel aspect is .8889
For computer screens the pixel aspect ratio is 1.000


Here's the algebra
for TV
720/480=1.5x.8889 =1.3333
for computers
640/480=1.333 x 1 =1.3333

Same result different numbers to get there!


Delphinus Wrote:
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> Although I have been editing on FCP for over 10
> years now, here's a queation I never thought of
> asking ... until now. Why does FCP edit in 720x480
> instead of 640x480?