WDM Video Capture Driver
for Bt848 / Bt849 / Bt878 & Bt879 Chipsets.

You need
Supported Cards
Custom Card Support
Known limitations
Microsoft Bugs
A bit of History
Contact Info
Contribute to the Cause
Useful links
Sourceforge page
Known problems / Limitations
  • There is a Bug in the Microsoft ACM (Audio Compressor Manager) that causes AVI capture to lock the computer at the end of the Capture Process in Win98SE and WinME. Apparently Microsoft is waiting for the WDM Audio driver of the sound card to complete all the passed buffers AFTER stopping the audio and video stream, but the default behaviour of the audio WDM driver is to simply cancel (maybe pause) all those pending buffers, but NOT to complete them, so buffers wonīt ever be completed. Despite this, the ACM is waiting for those buffers to be completed before returning to the application... This wait has a timeout period of 2^32 ms , so, Windows will seem to the locked for a very long time... I would suggest two workarounds for this: Donīt capture AVIs with audio, or just wait for the timeout to occur (A very long wait 8( or , use a hacked, not supported by me, version of the offending 16 bit DLL msacm.drv (you must replace the original one that is in \WINDOWS\SYSTEM ) that has a timeout of 2 seconds, far better than 2^32 ms!. This DLL is from WinMe, so I donīt know if it will work with other Windows versions... Donīt know if WinXP or Win2000 has the same bug). Ideally, we should expect Microsoft to fix this problem in the near future. An other Workaround is to use a DirectShow capture Application to capture without using the ACM. This is true for Uleadīs MediaStudio when capturing in MPEG. ACM is NOT used in this case, so there are NO problems... Get the DLL. This DOES NOT happen with Win2000 or WinXP so no need to do anything with those OS.
  • No support for the audio part of the Bt878 chip. I think that no card is currently using this. All the cards I have seen use the main sound card installed in the computer to digitize audio... Nowadays, I have discovered that there are some cards that are using the audio part... As i don't have one of those cards, it is impossible for me to add support for the audio part... And you should know that you can get more quality from your sound capture card... (There are some unfortunate users that have capture cards that only provide audio using the audio part of the Bt... Those users will have to wait until i buy a card that has an audio part (Bt878 based), as mine has a Bt848.
  • Overlay mode in VFW applications sometimes works, sometimes does not work. This is a problem with the Microsoft WDM to VFW wrapper, that all VFW based applications will use to use this driver. That wrapper is trying to open the preview channel at full frame size, at the same time of the capture channel, so driver will have to prioritize capture over preview. Please, select Preview mode instead of Overlay mode in all VFW apps to solve this. All DirectShow based applications won't show this problem if used in QCIF (half maximum Y size or less). This is a Hardware limitation of the chipset: It uses one of the fields to get capture and the other for Preview. So, if you want to capture at full frame size, you must use both fields at the same time. So, in this case, you won't get Preview in DirectShow based programs, or Overlay mode in VFW based programs.
  • Under Pal N Combination, maximum size is 754x576. this is a Bt chipset limitation.
  • The programs that where bundled with your card will probably stop working. They were written for their specific drivers, and are depending on some custom features (that this driver implements in a DirectShow compatible way, probably incompatible with the custom way they were implemented in the original drivers. Use third party programs to accomplish all the same tasks. For example AMCap, an example program that Microsoft gives you with their DirectShow/DirectX SDK, will let you do the same things that you used to do with the bundled software of your card.
Đ Eduardo José Tagle Powered by SourceForge
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