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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.
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