As I'm sure you are starting to realize, VirtualDub is one of the
easiest to use and yet most useful video editing tools you will
ever find. But I still get quite a lot of emails asking how you
can crop and resize video files, reduce noise, add logo's or other
cool effects with it. This is what this article is about. VirtualDub
can do all these things and much, much more! There is no need to
explain in detail absolutely everything it can do, because once
you've read through this guide you will get the idea and be able
to apply that knowledge to everything you want to do.
Video Editing Formats
If you are going to edit and/or compress a video using VirtualDub
or any video editing package then the better the original video
the better the final result will be. If you are capturing from a
TV Tuner or Video capture card use the highest settings you can
without going overboard. For example, there is probably no need
to capture a video at 640 x 480 pixels if you are going to resize
it to 352 x 240 anyway because not only will this take a lot of
time to do but it will take twice the hard drive space too. Whenever
possible you should capture with CD quality audio (16 bit 44100Hz)
and at the TV standard framerate (25fps for PAL TV and 29.97fps
NTSC). Usually capturing to MJPEG will produce the best results
and will be the easiest format to edit. For more details on video
capture check out my capture guide Here.
Compressing a Compressed File
Why not just compress straight to Mpeg or DivX I hear you cry!?
Well, you can, but don't forget that if you are going to resize
or apply any filters to a video file it must be recompressed
again! This is not VirtualDub's fault, every existing video editing
package is the same! For example, its no good compressing a DVD
video into DivX and then opening it up to resize it or crop
it because to resave that file you will need to recompress it to
DivX again. As you can imagine if the video is long then this could
take a long time. And since all formats I know (except Huffyuv and
uncompressed AVI) compress by discarding fine details, each time
you recompress the video some quality will be lost! As you can see,
it makes sense to make sure that the initial file as good as we
can get it.
Open your movie file in VirtualDub by going to File
> Open video file...
Select File > Filters
Press the Add... button (A)
Up pops a list of all the filters that can be applied to a video
file. Choose the one called: Null Transform.
Yes, I know, a weird name that 'null transform' isn't it. But press
OK and we're back to this box. Press
the Cropping... button (B)
Up pops the cropping box (below). Use the slider bar and frame
movement buttons to find a good part in the video where you can
see clearly where you need to crop. Then change the numbers any
of the four number boxes X1,
X2, Y1 or Y2.
Each box represents one of the four sides of the box. Simply increase
or decrease the amount needed and you will see it crop before your
eyes :)
When you are done press OK.
That's it! When you resave the video in VirtualDub the newly saved
video will be cropped. But don't forget that you need to recompress
again when you save it or it won't work. Cropping is especially
useful for getting rid of any hum-bars from the edges of the screen
that usually appear with TV Tuner captures.
Resizing is just as easy, go to: File >
Filters
This time press Add... and select
the resize filter.
Up will pop this box. Just type in the new width and the new height.
Then select Precise bicubic from the filter mode. Bilinear is best
for shrinking images and bicubic is best for enlarging. Nearest
neighbour is the fastest but gives lowest quality for everything
but simple shapes.
You can choose the show preview button too to see how it looks.
It is important to remember that, if you intend on compressing the
video into Divx (or in fact many other formats), your final movie
sizes should be multiples of 16 pixels! Sometimes they only need
to be multiples of 8 pixels and sometimes (very rarely) they need
to be multiples of 32 pixels. As an example, a 352 x 288 video will
compress into Divx without problems, but a 351 x 288 will not!
Filter Order
VirtualDub filters are executed in a specific order. The one at
the very top will be executed first and the one at the bottom of
the list will be executed last.
It may not seem to matter what order they effect the video, but
it is an important point. Lets say, for example, you wanted
to resize a video from 704 x 576 to 352 x 288, but you also wanted
to apply filters to sharpen the image. If you put the sharpen filter
first in the list it would take twice as long to convert when you
tried to save it! This is obvious because it takes twice as long
to sharpen a picture twice the size. It would be far quicker to
sharpen the image after it had been resized smaller. Because
of this, VirtualDub has two buttons called 'Move up' and 'Move down'
that allow us to move the order of the filters up and down.
PROCESSING IT
When you are finished all the filters will be applied
to the video file you save. Now you must choose the final format
you want the video to be. You can, of course, use any video format
VirtualDub offers, but just to illustrate, if you wanted to make
it to Divx this is how you'd do it.
Go to: 'Video > Compression...'
Up pops the following box below. Choose Mpeg-4 Low-Motion
and hit the configure button (highlighted in red).
Then up pops the codec options. Use one of the bitrate
calculators that can be downloaded from Digital Digest to make sure
the movie will fit into the size you need. 650kbps will usually
fit any movie on a single CD, but you can usually get away
with between 900 and 1000kbps for a 352 x 240 VCD movie for better
quality see my quality guide if you are unsure about correct bitrate
settings.
Audio Compression
Now select the audio settings by going to: Audio
> Full processing mode (so the black dot appears by it).
Then Audio > Compression.
Up pops this box below. Choose Mpeg Layer 3 or Divx
;-) Audio 64kbps, 441 kHz, stereo. And press OK.
That's it! Save AVI...
Okay that's it for this one. Check out part two and
I'll try and explain a few more tricks =).
Duplication of links or content is strictly
prohibited. (C) NICKY PAGE 2000
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