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Visual Basic.NET 2005 |
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Description: |
AVICapture is a Visual Basic.NET 2005 partial
implantation of Video for Windows (VfW) |
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Sample: |
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Introduction
AVICapture is a Visual Basic.NET
2005 partial implantation of Video for Windows (VfW) (http://msdn2.microsoft.com/en-us/library/ms713492.aspx).
It is implemented with great help from “A Simple C#
Wrapper for the AviFile Library” by Corinna John which
can be found at
http://www.codeproject.com/cs/media/avifilewrapper.asp.
Although there are an immense
variety of things you can do with VfW, my need was to
create an AVI with compression from a series of images,
specifically the screen capture of a Windows form or
control. AVICapture only implements the functions
needed to write a series of bitmaps to a compressed AVI.
Rational and Background
The basis of this project was to
create a Yahoo! Messenger webcam capture utility. The
first step in doing this is to find a way to save the
captures to a video or AVI. After many hours of
searching I could not find a suitable library.
Additionally the ones that came close were commercial
pieces of software that had with a very high price tag.
The only solution was to create my own library.
From the beginning I had the choice
between Video for Windows and DirectDraw, both Microsoft
technologies. It appeared that VfW was more straight
forward so I flipped a coin and started in that
direction. After A LOT of Microsoft API documentation I
was fortunate to find “A Simple C# Wrapper for the
AviFile Library.” This AVI library has everything but
the kitchen sink and is well written. I have a very
specific application so I carved out what I needed from
the wrapper and combined it with what I already had.
Writing an AVI creator was not as
easy as I predicted. The documentation is lacking and
there are many pitfalls to watch out for.
Features
- Creation of an AVI file from a
series of bitmaps.
- CODEC compression.
- CODEC selection
Usage
The first phase is to prep the many
variables. You will have to know how large the bitmaps
will be (they can not dynamically change size), where
you want to save the file to, and frame rate. In the
following example I take a Windows form as the source.
Dim rectWindow
As SC_APIs.RECT
SC_APIs.GetWindowRect(hWindow, rectWindow)
iWidth = rectWindow.Right - rectWindow.Left
iHeight = rectWindow.Bottom - rectWindow.Top
'Create the bitmap
Dim bWindow
As
New Bitmap(cInfo.iWidth,
cInfo.iHeight)
Next I
set the filename and frame rate.
strSavePath = System.Environment.CurrentDirectory +
"\"+
"test.avi"
iRate = 1
Then a new AVICapture object is
crated by calling the following
AVIInstance = New
AVICapture.AVICapture(strSavePath, iRate, iWidth,
iHeight)
You can optionally set a CODEC to
record your AVI with. By default AVICapture will use
the Cinepak Codec by Radius if none is selected. CODECs
are interesting creatures that do not always work as
planned. For some reason many of the default Windows
CODECs crash when used so use this feature with caution.
dim
_uAVICompressOpt As
AVICapture.AVI_APIs.AVICOMPRESSOPTIONS_CLASS
Dim fiCODEC
As
New
IO.FileInfo(System.Environment.CurrentDirectory +
"\CODEC.avi")
Dim AVIInstance
As AVICapture.AVICapture
= New
AVICapture.AVICapture(fiCODEC.FullName, 1, 1, 1)
_uAVICompressOpt = AVIInstance.returnCODEC()nCODEC()
fiCODEC.Delete()
Once AVIInstance has been created
it is ready for you to add frames. Call the addFrame
function for each new frame.
AVIInstance.addFrame(bWindow)
Unlike DirectDraw, VfW does not use
an internal clock. This means that the run time of the
created AVI does not depend on the time between a call
to addFrame. If you specified a frame rate of 1 and
added 3 frames then you would have a 3 second movie even
if you waited an hour between addFrame calls. For the
above example to be effective you should add a timer
that calls addFrame at the same interval as the rate.
There is a companion project with
AVICapture called YCC Form Capture which demonstrates
how to use this library. YCC Form Capture is a generic
Windows form and control capture utility.
Bugs and Gottchas
- Some CODECs fail. Creating an
AVI file can be a taxing experience and half of that
trouble is in compression. AVICapture is based off
of “A Simple C# Wrapper for the AviFile Library” on
The Code Project. Unfortunately the base project
has the same bug and I have not found a solution.
Requirements
License Agreement
The software, AVICapture, is distributed under
the Creative Commons GNU General Public License
which can be found at
http://creativecommons.org/licenses/GPL/2.0/
The major points follow:
- No commercial distribution without
permission.
- You are allowed to modify the program and
source, all I ask is you keep the original
credit.
- If you do modify the program it will fall
under the same license agreement.
I have chosen this license to allow users to do
pretty much what they want with the program. The big
thing that I ask is please don't redistribute this
software without acknowledgment to YCC and a link
back to http://ycoderscookbook.com. I would love to
hear what you think about the program and if you
have made useful changes. A forum for AVICapture
can be found at
http://www.ycoderscookbook.com/forums/
under the Programs directory.
As with any piece of freeware, I have made every
effort to make the software useable and friendly.
With that said I take no responsibility for damage
created by this program or the user’s actions. The user takes full
responsibility for their actions.
Source
Full source code is provided.
Please feel free to modify AVICapture as long as
you read and understand the license agreement.
I have created a place on the forum where all users
can discuss AVICapture at
http://www.ycoderscookbook.com/forums/viewforum.php?f=14.
AVICapture Executiable
AVICapture Source
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