Some people are real sticklers for getting perfect aspect ratio.
But it's almost impossible to get a perfect aspect ratio when we
are limited to resizing by 16 pixel jumps every time! It makes cropping
awkward and it also limits us to weird sizes. I have to admit that
I haven't always followed perfect aspect ratios but this time
I think I've got it right.
AN ASPECT RATIO OF 4:3
The picture below is taken from a 4:3 DVD. If your
DVD is an aspect ratio of 4:3 then there's nothing to it! All PAL
(European) DVD's use 720 x 576 pixels and all NTSC (north American)
DVD's use 720 x 480 pixels. This means a perfect aspect ratio should
And, since we must resize in blocks of 16 x 16 pixels, this makes
the following the closest sizes. Remember that the closer to 1.33:1
it is the more exact the aspect ratio to a 4:3 TV screen:
720 x 576 / 720 x 480
720 x 544
640 x 480
592 x 448
544 x 416
512 x 384
448 x 336
400 x 304
384 x 288
336 x 256
320 x 240
For DivX rips I'd recommend something like 448 x 336 or even 384
x 288 for PAL and for NTSC you can go as low as 336 x 256 since
you're used to 20% less TV resolution than the rest of the word,
he he! I've tended to change my mind a lot on what I consider to
be the best sizes to use, but I shy away from very large sizes because
they cause too many artifacts. Also, full DVD resolutions will very
often cause jerky playback. This will happen as often as the Divx
hits a keyframe. For my 500Mhz CPU the DivX codec seems to give
an optimum smooth playback with under 1000 blocks of 16 x 16 pixels
before problems. Therefore a full 720 x 576 resolution DivX with
1620 blocks is no good for me. If you intend on making DivX's that
will play on just about anyone's machine, then I suggest you consider
ANAMORPHIC ASPECT RATIOS
Here is where life gets tricky. Firstly, many DVD's will
say something like: 2.35:1 Anamorphic (Approx.) the "approx"
part doesn't inspire confidence in me =). If you have read the section
on Anamorphic DVD's you will know that they rip at 720 x 576 (or 720 x
480) and will give a squashed picture like this one:
For those of you who use Flask Mpeg the rest of this information
may not be needed. Because, if you check the maintain aspect ratio
option, it will stretch the movie to the correct shape for you.
But you still may have problems with those god accursed NTSC movies!
Hence, the following information will be useful for getting correct
aspect ratios in Flask when you keep the aspect ratio option turned
STRETCHING 16:9 / 24:10
2.35:1WideScreen is probably the most used
anamorphic size in Europe. But because we are limited to 16 x 16 blocks
(because of the limitations of the mpeg format), the only size that is
exactly 2.35:1 is 640 x 272 pixels. Actually, its an aspect ratio of 2.35294117647059:1
if you really want to impress your friends =).
These are some of the closest:
672 x 288 (2.33:1)
640 x 272 (2.35:1)
528 x 224 (2.36:1)
But that's a bunch of bunk though! If you just resize
an anamorphic DVD to 2.35:1 you'll see the incredible pancake show!
This is basically because even anamorphic DVD's are still recorded
with black bars at the top and bottom of the image. DVD's only support
4:3 and 16:9 aspect ratios. In other words they can be either 1.33:1
or 1.85:1. If another size is needed such as 2.35:1 then they will
squish the picture on the DVD itself so that when it is resized
to either 1.33:1 or 1.85:1 it will look the correct shape. This
means the following sizes are the most common to use. The closer
to a ratio of 1.85:1 the better.
720 x 576 / 720 x 480
720 x 384
640 x 336
576 x 304
512 x 272
480 x 256
448 x 240
USING CM'S DIGITAL VIDEO TOOL
I cannot list every possible situation. So instead,
there is a great utility called CM's Digital Video Tool. It can
do many things, but its most useful feature is its ability to calculate
aspect ratios for us. Get the application Here.
Lets assume you want to resize your movie to be somewhere
between 550-600 pixels across in size. It is an anamorphic 2.35:1
movie so we must use the aspect ratio of 1.85:1 to put it right.
Right, so we open Digital Video Tools, select the 'Datarate Calculator'
tab and click on the bit I've encircled in red.
It will change to the following display:
From the drop down menu you can choose some standard settings
such as 4:3 or 16:9 etc. But you can ignore this drop down menu completely
if you like! The most important thing is to make sure the 'Align by 16'
box is always ticked and the 'Lock aspect' box is not
ticked until I tell you :). Then follow these three simple steps:
Move the slider bars left and right until you get the
correct aspect ratio you need. It will appear in the box
to the far left of the picture (in the picture above it is:
1.80:1). Forget the size settings on the right (in the picture
above are 720 x 400). The important thing is to get the aspect
ratio correct. If you cannot get it exactly then get it as
close as possible. So, for example, if you cannot get 1.85:1
you could use 1.86:1 and it would still look almost the same.
Once you know the aspect ratio is correct tick the 'Lock aspect'
box to keep it always the same.
Finally, move either slider bar until the movie is the resolution
you want it. For example, I moved it down to 576 x 320 and this
gave me a pretty close aspect ratio to1.85:1 because I wanted
the video 576 wide.
That's it! Now you should be able to figure out any aspect
ratio you want. But here are some helpful guidelines to save some
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