Correct document size for Flash animation --> DVD ?

When creating Flash animations / movies that are intended to be output
to DV or DVD, .. what is the correct document size to use when
animating and exporting? Is it 720x534, 720x540, or 720x528?? If you
sift through these NG archives, .. you'll notice an ongoing debate
about these different frame sizes, and I was wondering if we've all
come to a conclusion on this as of yet.

I intend to export the animations as either AVI files or PNG sequences
(depending on whether I need a transparent alpha channel) -- and to
process / export them in AfterFX. So which size, then, should I use?
720x534, 720x540, or 720x528 ?

Thank you,
-yvan

 

Depends on your target video standard (which you did not specify.)
If 625/50 ("PAL"), output at 788×576 and resample to 720×576.
If 525/59.94 ("NTSC"), output at 720×527 and resample to 720×480.

To get the best possible motion smoothness, render 50 frames
per second for PAL and 60 (59.94) frames per second for NTSC.
Then convert these full-resolution frames to interlaced fields
by combining the odd and even lines from adjacent frame pairs
with AviSynth (or a similar tool.)

 

See, -- yet another frame size is being suggested!! Sorry, but I
don't buy it. I'll need a technical explanation as to how the odd
720x527 dimensions are derived. Can anyone here support or contradict
what this person is saying?

Thank you,
- yvan

 

Very well then, here is my web page on the subject:

<http://www.iki.fi/znark/video/conversion/>
<http://www.iki.fi/znark/video/conversion/#4.7>

 

Very interesting article. I had your page bookmarked already,
actually. Based on what you've written, I gather that your rationale
is that the 720x527 frame size actually serves as the "happy medium"
between the different rectangular pixel formats. Is this correct?

May I ask what kinds of graphics and video editing software you are
using to put your theory in practice? I ask because although your
numbers may pan out in theory, they actually might not work well in
practice when dealing with certain consumer-based video editing
applications, like Adobe Premiere.

Cheers,
- yvan

 

That "happy medium" thing is only coincidental. The rationale
is more like

1) 720x540 represents an exact 4:3 frame in square pixels,
so it would at first glance seem reasonable to use it for
square-pixel (animation etc.) work which will end up in
non-square-pixel formats in the end...

BUT

2) ...720x480 (in ITU-R BT.601 pixels) is _not_ an exact 4x3
frame (no, not even if you take the non-square pixel aspect
ratio in account), ...

YET

3) ...many people insist that direct vertical scaling from
720x540 to 720x480 and back again is ok (not understanding
the point number 2, or arguing against it.)

Once you take the pixel aspect ratio (or rather, the sampling rate)
in account and calculate what part of the video signal is covered
by 720x480 and what would be a square-pixel equivalent of that area
if the number of samples in the horizontal direction is kept constant,
you will end up somewhere near 720x527.

However, some video codecs do not allow storing frames using any
other pixel size than multiples of 2, 4, 8 or 16. This might be
the reason why some people recommend using 720x528 instead: 528
is evenly divisible by 16 (and 8, and 4, and 2), and is therefore
a more "practical" number when dealing with various codecs. (It
is still off by one pixel row, but the difference is small enough
to go unnoticed, and if this single-pixel disrepancy really annoys
you, you could quite easily fix it by using 720x528 only as a
temporary format and cropping off the last line on the fly just
before resampling to the target format.)

VirtualDub, AviSynth, Premiere.

Living in a PAL-B/G country most of the square-pixel work I do
is in 788x576. (This is the square-pixel equivalent of the signal
covered by the 720x576 area in ITU-R BT.601 13.5 MHz pixels.)

Premiere defines the PAL DV pixel aspect ratio as 1.067 (y/x) in
its 4:3 PAL DV templates. This is definitely wrong, but it does
not matter much for the type of editing I do. If I am merely
cutting and mixing DV video, all my material is already in the
720x576 format (as sampled by the camcorder, not Premiere), and
Premiere does not actually need to know the pixel aspect ratio,
as the size of the frames is not being touched at all in the
process.

As for imported graphics, I usually prepare everything in
graphics apps (such as GIMP and the like) using the 788x576
format, then convert to 720x576 as the final step - in the
graphics app, not in Premiere - before importing to Premiere.
As the imported still frames have already been prepared into
the 720x576 format, Premiere just passes them on the timeline
as they were in the file, without doing any resampling on its
own, so the pixel aspect ratio issue is avoided this way.

As for standards conversions, format conversions, frame size
conversions - well, I use VirtualDub and AviSynth for all that,
and calculate/enter the numbers by hand, so Premiere's idea of
pixel aspect ratio - once again - does not affect the end
result.

Of course, the idea of fixing the wrong pixel aspect ratios in
Premiere's DV templates has occurred to me many times; it is
just that I have not personally had any practical need for it
as I have not let Premiere do any resampling on its own.
(It might be different if I needed to do lots of complicated
compositing in After Effects or some such, but I do not even
own AE.)

* * *

Anyway, here is a little something you might want to try out if
you are interested in tweaking the profiles. (I am using the PAL
DV profile here as an example, but things should work the same
way for the NTSC templates too - just use different numbers):

As mentioned above, the PAL DV templates in Premiere define
the PAL DV pixel aspect ratio as 1.067 (y/x), which is wrong.

A closer look in the actual template file (which lives in the
"Settings\DV - PAL\" directory with the name "Standard 48kHz.prs")
in a text editor reveals the following setting:

pixelAspect=50332368

This is a decimal number, and in itself looks like unintelligible
gibbersh. But let's convert it to hexadecimal:

50332368 (dec) = 030002D0 (hex)

Still looks like gibberish, but trick is that the number actually
comes in two parts: 0300 and 02d0. Let's convert them back into
the decimal system separately:

0300 (hex) = 768 (dec)
02d0 (hex) = 720 (dec)

So, this is how Premiere actually stores the pixel aspect ratio.
768/720 = 1.0666... or 1.067.

It is now trivial to define a custom aspect ratio. We can use the
number 702 instead of 720 (since the PAL 4:3 area is really 702×576
in DV pixels and 768x576 in ideal square pixels.)

We already know that 768 (dec) = 0300 (hex). Converting 702 (dec)
to hex gives us 02be. The new hexadecimal number fot aspect ratio
is therefore 030002be (hex), which is 50332350 in dec.

Now we can simply change

pixelAspect=50332368

to read

pixelAspect=50332350

And now Premiere displays the pixel aspect ratio as 1,094 (as it
should.)

Some notes:

- Changing the value seems to work, but I have not done yet any
practical testing on how Premiere's import/resample feature works
after this change, so further testing would be needed to figure
out whether everything is OK after this change.

- I am not sure if there is any difference in using 768/702 or the
simpler form 128/117 (which would be 0080 0075 in hex and 8388725
in decimal.)

- As for NTSC profiles, my recommended value would be either 648/711
(0288 02C7 in hex, 42468039 in decimal) or 72/79 (0048 004F, 4718671.)
(see <http://www.iki.fi/znark/video/conversion/#conversion_table>.)

- Premiere has a couple of built-in aspect rations with descriptive
titles, such as "D1/DV PAL", which are hardcoded into preminfo.dll,
and which will (still) show up in the listboxes in project settings
even if you change the aspect ratios in the profile files. With a
hex editor and some luck, one might be able to change these, too,
but I'm inclined to think it is just a cosmetic thing and not
worth tinkering with.

* * *

I do not have the time to do any extensive testing of the effects
of these profile changes right now, but if someone does, it would
be nice to hear some reports about it. (For After Effects as well,
if there are similar profiles in there.)

 

Just noticed there is also "cappixelaspect=50332368" in the same file,
presumably for setting the pixel aspect ratio for captured video. Any
changes made to the "pixelAspect" setting would probably need to be
copied to "cappixelaspect" as well.

 

Shouldn't this be 768x576?

 

No, not really:

702x576 in ITU-R BT.601 (DV/DVD) pixels = 768×576 in square pixels
704×576 in ITU-R BT.601 (DV/DVD) pixels = 770×576 in square pixels
720×576 in ITU-R BT.601 (DV/DVD) pixels = 788×576 in square pixels

My target format is the normal DV/DVD frame (720×576), so I use a
square pixel frame of equivalent dimensions (788×576) for my square
pixel work.

If I used 768×576, I would first have to resample to 702×576, then
add 9 pixel black borders on both sides (to get the final 720×576
frame in DV pixels, and in order not to distort the aspect ratio
of the images.)

See <http://www.iki.fi/znark/video/conversion/> for more information.