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  • Resizing and Cropping a DivX in Mpeg2avi

    If you want to fit a movie into the smallest possible size, cropping can do a lot to help out. The most vital thing to remember for optimal compression is to always crop a few pixels into the image and delete all of the black bars. Mpeg compression works best on blurry images; so if a hard black line is seen at the bottom or top of your cropped movie it will not compress as effectively. In fact, if you cannot crop into the image then I'd say don't bother cropping at all.

    Because Mpeg2avi doesn't have a preview box we will have to do a few quick tests to see what we will get. The best way to do this is to set it up to encode about 100 frames. Mpeg2avi has a start and end from such and such a frame option. So we can put in where we want to test the movie and how many frames to encode. This is done like this:

    This will make it jump 2000 frames into the movie and encode 100 frames of it. Then we can see what the picture will look like. It is also a good idea to start from the second Vob so we don't get the start credits. Now, every time we want to see what the image looks like we simply hit the 'Create my AVI' button and in a few seconds we can check it.


    Many get confused by Mpeg2avi's crop and resize settings, but really they are very easy enough to use. The only down side is you don't have an instant preview to work from like Flask Mpeg. As always we are using Danni's amazingly cool GUI to do this, so you will not need to mess around with the DOS prompt =).

    Okay, lets do this: assume we are resizing a 720 x 576 PAL DVD to 448 x 336 this is a 4:3 aspect ratio of 1.33:1. Mpeg2avi's resizing options are:

    Downsizer X: This option shrinks the width smaller according to the size you set it.
    Downsizer Y: This shrinks the height according towat you set it.

    It's important to remember that the downsizer options only shrink the picture itself. So, for example, in the picture below the original movie was 720 x 576 and I used a downsizer of:

    Now, the movie below is still 720 x 576 but the picture inside it is 448 x 336!

    To get the movie perfect we must crop out the black areas too. The Mpeg2avi crop functions are:

    Output Cropping X: crops the width of the whole window. Note that its doesn't just take a bit from one size or the other but takes it evenly.
    Output Cropping Y: same again, but it crops the top and bottom.

    So to crop out the black areas we just put the same resize values in the cropping sections as are in the resize, like this:

    The final picture will look like this:



    The same process is used again, but because Widescreen movies don't always use the same sizes we may have to "tweek" the measurements a little to get the best posible cropping. Lets say we have a 2.35:1 Anamorphic movie. Its 720 x 576 and looks like this:

    As you can see anamorphic DVD's have squashed pictures. For an explanation of this subject be sure to read the section called "Anamorphic DVD's & Aspect Ratios" in the my appendix. But to cut a long story short we will resize the image to an aspect ratio of either 1.85:1 (or 1.33:1 depending on the DVD) and I want to resize my movie to about 576 x 320 which is the closest size I can get to a correct aspect ratio at this size. So I put:

    When I check the move it is now in near-perfect aspect ratio:

    Next is to crop out the picture. Since we know the correct width is 576 across we can set the cropping to 576. We also know that 320 will be higher than the picture because we have resized the picture to Y=320. So lets put that in too like this:

    And we get this:

    But because the DVD had a gap on the left, this is going to detract from our otherwise perfect cropping. All it needs is to bring the sides in 16 pixels and it will look nice. So instead of 576 we can crop it to 560 or we could resize the image 16 pixels to so it was 592 x 336. So we:

    And we get the following:

    Finally we keep cropping a little at a time until we get the bottom and top right. At the moment the cropping is Y=320. We want that to be smaller so we take away 16 pixel to make 304 (always resize by multiples of 16 pixels). Thats no good, so we take off 16 more until its 288 and try that. Then we try 272, then 256 and finally we find that 240 is perfect! So we put:

    And the movie is cropped perfectly and has perfect aspect ratio!

    I'm not joking when I say that cropping like this really does improve the picture quality. More bitrate can be assigned to the image and less to keeping those sharp black lines! Forget what all those morons say about how a DivX can rip full DVD resolution! Even if you want to use 2 or 3 CD's to make them! Video CD's are 352 x 240 pixels and look almost as good as VHS videos when played on a TV. Our cropped DivX is exactly the same height and almost double the width, and, when done right can achive as good or better quality than a VCD and yet still fit onto a single CD. Don't use crazy large sizes - do it right!

    Final Warning

    Finally, its only fair to warn you that, athough in my opinion cropping improves the image quality of the DivX rip by a lot, before you decide that cropping is the best way to go, you must consider these four facts:

    1. A cropped movie is sometimes harder to convert into another format. This is because you may need to re-add the black bars to the top and bottom of the movie first or the movie may be stretched out of shape.
    2. A cropped DivX movie will play at the wrong aspect ratio in PowerDVD and some other Video players. On the other hand, Media Player, MicroDVD and many other players will play back a cropped movie perfectly.
    3. VCD's and SVCD's cannot be cropped if they are to be played in a standalone DVD player because it will not accept them.
    4. Finally, Mpeg-4 files (and DVD files for that matter) have problems playing back on some hardware if they are not encoded in sizes that can be divided by 32. This means the Matrox G400 or the Nvidia GeForce would probably have problems outputing it to TV.
    For example:
    A 528 pixels wide size divided by 32 = 16.5. This is not a multiple of 32 and so may have trouble.
    But a 576 pixel wide size divided by 32 = 18. This is a multiple of 32 and will play back perfectly.

    Duplication of links or content is strictly prohibited. (C) NICKY PAGE 2000