Hi -
A followup (but in a new thread since I didn't save the earlier
message) to the earlier "constrains and aspect ratio" posting. It
dawned on me that my arithmetic (or at least the explanation of the
end result) was faulty.
I'd proposed:
> for 768x576 (square pixel) input you would add:
>
> ... | y4mscaler -I sar=1:1 -O sar=PAL -O size=720x576 -S option=sinc:4 | ...
>
> If you do the arithmetic you will see that 768 square pixels is
> exactly the same as 720 59:54 pixels.
Not quite correct. I made the assumption that the desired
output framesize was the DVD 720x576 framesize. The above y4mscaler
command will do that BUT will need to pad by 8 pixels on each side.
The padding is because the PAL (well, ok - 625line) frame size is
really 704x576. The arithmetic: 768 * (54/59) = 702.91 which is rounded
up to 704. Thus for a 720x576 frame there needs to be 8 pixels added
to each side of a 704x576 frame. Don't worry about seeing those padding
pixels on the DVD - the edges of a picture are lost in the typical
TV overscan.
You could, if desired create a 704x576 frame with no padding by:
y4mscaler -I sar=1:1 -O sar=PAL -O size=704x576 -S option=sinc:4
For NTSC (525line system) the square pixel full frame is 640x480 and
the rectangular pixel (10:11 ) frame is 704x480. The DVD frame size
of 720 is achieved by padding a 704 frame with 8 pixels on each side.
I hope that clears up the confusion that was accidentally caused
earlier.
Cheers,
Steven Schultz
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