Re: TV stream and scrambled channels

"David Olsson" <david.olsson@xxxxxxxxx> schrieb im Newsbeitrag

You will however have to "read" any information you need out of the
"raw"
ts-packets - MS-Digital-TV infrastructure knows nothing about
ca-systems/scrambling.

Ok, this makes sense! I just need to study the mpeg TS specifications to
recognize certain interesting packets.

yes, all the information is out there - esp. iso13818 and some more
documents from etsi(.org I think)

So for your "software CI" to work you will also have to do the actual
descrambling yourself (which is basically nothing but a simple
xor-operation) - there are some dvb-s programs out there that implement
an
interface for software-cams - you could have a look at their
source-codes
(basically they take each 188byte-packet coming in with the TS, examine
it
if it has to be processed/process it and then pass on the modified
packet)
...

But what if I have a DVB tuner with embedded mpeg-decoding? Will such a
tuner even allow scrambled packets to leave the BDA driver if the tuner
isn't able to decode them? Or will all packets be sent along to the
filter graph and, if neccessary, be handled by my and all other filters
and then fed back to the hardware decoder by a filter further down the
filter graph?

I think you're mixing up hardware _decoding_ (which would result in an image
ready to present on screen) and hardware _demuxing_ (which "pre-selects")
which packets to transmit out of the bda-capturefilter.

If you really have hardware-mpeg2-decoding (which e.g the technotrend dvb-s
_premium_ line has) then you're completely out of luck, unless the
bda-drivers would present to you some kind of custom interface for supplying
descrambling-CWs. I do know of _NO_ card/driver that has these caps (nor do
I think there would be a legal use for such an interface).

If your card can do hw-demuxing (which almost all dvb-capture _hardware_
COULD do, but almost no driver implements), then this should not influence
any scrambling/descrambling you wanted to do with the resulting stream.

I guest that, if I really had a DVB tuner with hardware mpeg decoding, I
could test what kind of filters a filter graph that displays a TV
station from the DVB stream is made up of this using GraphEdit?

If your card has hw-mpeg2 _decoding_ then you won't be able to test this
with graphedit, because this is certainly implemented by some means
_diffferent_ from standard ms-digital-tv/bda graphs...
Even hw-demuxing will be hard to test with graphedit, because you most
certainly will have no UI to configure the hw-demux. Only the ms-mpeg2-demux
presents such an interface (which pids to map). However a complete BDA-graph
with Network-Provider and BDA-TIF might work in graphedit.
--
Peter Feldbaumer
p dot feldbaumer at utanet dot at


.

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