Hello,
I'm using a cheap bttv grabber card (the bttv-module uses card=37, i.e.
'PixelView PlayTV pro'). My card is no PixelView PlayTV pro, but the card specs are
equal.
When I grab a series of images (I can supply my code if this helps in answering my
question) the following problem occurs seemingly at random:
For one (or a few) frame(s) the first field is not grabbed. Lets call that
frame x. Instead the second field of frame x and frame x+1 are grabbed and stored into
the same memory location. The result is a picture which consists of field one of frame
x-1 and the second field of frame x+1.
I feel that this is because the grabber hardware does somehow miss the sync
signal of the first field of (at least) two consecutive frames and as it has to grab
two fields it just grabs two second fields without changing the grab-buffer. And
because of the state (inverted or not?) of the sync signal the driver also correctly
identifies these two fields as beeing two second fields which means it will overwrite
the first with the second.
I also guess that similar problems will occur when only one sync signal is missed.
Then the grabber will put field 2 of frame x and field1 of frame x+1 into the same
image, etc. Unfortunately I do not yet know how to diagnose this. For the above case,
that always the first or the second field is missed I have written an analysis
software, which says that in all cases only field 1 was missed and never field2.
My question is, of course, how can I stop the driver from making mistakes like that,
or how can I diagnose such mistakes? Also, how can I force the grabber to only start
grabbing on the first field? Or how can I grab half frames, i.e. only one field at a
time? Or how can I detect that the grabber missed a filed or frame?
Bye,
Robert S.
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Robert S"utterlin ([EMAIL PROTECTED])
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adress: Giessenbachstrasse, POBox 1603, 85740 Garching, Germany
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