Correct document size for Flash animation --> DVD ?

Discussion in 'Amateur Video Production' started by Yvan J. Gagnon, Feb 12, 2004.

  1. 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
     
    Yvan J. Gagnon, Feb 12, 2004
    #1
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  2. Yvan J. Gagnon

    Jukka Aho Guest

    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.)
     
    Jukka Aho, Feb 13, 2004
    #2
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  3. 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
     
    Yvan J. Gagnon, Feb 13, 2004
    #3
  4. Yvan J. Gagnon

    Jukka Aho Guest

    Jukka Aho, Feb 14, 2004
    #4
  5. 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
     
    Yvan J. Gagnon, Feb 14, 2004
    #5
  6. Yvan J. Gagnon

    Jukka Aho Guest

    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.)
     
    Jukka Aho, Feb 14, 2004
    #6
  7. Yvan J. Gagnon

    Jukka Aho Guest

    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.
     
    Jukka Aho, Feb 15, 2004
    #7
  8. Yvan J. Gagnon

    Bariloche Guest

    Shouldn't this be 768x576?
     
    Bariloche, Feb 15, 2004
    #8
  9. Yvan J. Gagnon

    Jukka Aho Guest

    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.
     
    Jukka Aho, Feb 15, 2004
    #9
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