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Q99287: VidCap: Double Buffering Causes Dropped Frames

Article: Q99287
Product(s): Miscellaneous Windows Products
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 19-SEP-1999

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The information in this article applies to:

- Microsoft Windows Sound System, versions 1.0, 1.1 
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SUMMARY
=======

When using VidCap to capture a live video sequence, you may drop an
extraordinarily large number of frames if you have a line similar to the
following in your CONFIG.SYS file:

  DEVICE=C:\WINDOWS\SMARTDRV.EXE /DOUBLE_BUFFER

MORE INFORMATION
================

SMARTDrive 4.x provides the capability of caching both read and write
operations. If this "double-buffering" is enabled, data is written to the
SMARTDrive's buffer first, and from there to the hard disk. For optimal
operation, VidCap tries to stream data continuously to the hard disk. If
SMARTDrive is double-buffering, VidCap sends data to the buffer, and the data
stream is then interrupted as SMARTDrive writes to the hard disk. This can
result in either dropped frames throughout the video sequence, or all frames
after a certain point to be dropped (depending on the size of SMARTDrive's
cache.)

Double-buffering is required for proper Windows operation with some hard disk
controllers, but is only suggested as a general performance enhancer with other
controllers.

To reduce the number of dropped frames, you can try the following procedures:

1. Comment out the following line from CONFIG.SYS and restart your computer:

     DEVICE=C:\WINDOWS\SMARTDRV.EXE /DOUBLE_BUFFER

  For example, type the following to comment out the above line:

     ;DEVICE=C:\WINDOWS\SMARTDRV.EXE /DOUBLE_BUFFER

2. If Windows fails to operate correctly after this line has been removed
  (unexpected system hangs, disk read errors, or Windows failing to start), try
  opening SYSTEM.INI in a text editor such as Notepad and add the following
  line to the [386enh] section:

     VIRTUALHDIRQ=OFF

3. If Windows still does not operate properly, put the SMARTDrive
  double-buffering line back into CONFIG.SYS and modify the SMARTDrive line in
  AUTOEXEC.BAT to read:

     C:\WINDOWS\SMARTDRV.EXE /L

  The "/L" causes SMARTDrive to keep the buffer size small, which results in
  smoother data streaming to the hard disk.

Additional query words:

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Keywords          :  
Technology        : kbWinSoundSysSearch kbWinSoundSys100

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