Microsoft KB Archive/139977

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PRB: Video Window Moves During Playback

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Q139977

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The information in this article applies to:


 * Microsoft Video for Windows Development Kit
 * Microsoft Windows Software Development Kit (SDK) 3.1
 * Microsoft Platform Software Development Kit (SDK), on platform(s):
 * Microsoft Windows versions 3.1, 3.11
 * Microsoft Windows NT Server versions 3.5, 3.51, 4.0
 * Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0

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SYMPTOMS
The video playback window shifts position at the start of playback.

CAUSE
Microsoft Windows versions 3.1 and 3.11 along with Windows 95 automatically position the top-left corner (origin) of the video image (client area) at specific screen coordinates for playback performance reasons. Therefore, playback in a non-aligned client area can be slowed by up to 50%.

RESOLUTION
To avoid the window repositioning, an application must set the top-left coordinates of the window's client area in a correctly-aligned screen location prior to playback. Select the nearest x and y screen coordinates for the client area that are evenly divisible by 4. For example, use (12,12) instead of (13,13), and use (20,16) for (19,16) or (20,17).

There are no flags that disable the automatic alignment.

STATUS
This behavior is by design.

MORE INFORMATION
To provide optimal playback across the broad spectrum of video boards and displays supported by Windows, the origin of the video image is aligned along a 32-bit boundary. Client areas not aligned along 32-bit boundaries will cause the playback windows to be repositioned towards the upper-left corner of the screen. Aligning the video image on a four-pixel boundary helps achieve the highest frames per second.

Stretching playback may also slow performance down by 50%. In most cases, you should play the movie in its standard format unless stretching is required. For example, play a 320x240 movie at 320x240.

Additional query words: 3.10 4.00 3.50 alignment avi move vfw pixel pixels

Keywords : kbmm

Issue type :

Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351xsearch kbWinNT350xsearch kbWinNT400xsearch kbWinNTW350 kbWinNTW350xsearch kbWinNTW351xsearch kbWinNTW351 kbWinNTSsearch kbWinNTS400xsearch kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351xsearch kbWinNTS350xsearch