Re: TV stream and scrambled channels

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

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.

Nope, no mix-up. :-) But I haven't considered hardware demuxing. Would a
DVB tuner implementing hardware demuxing simply not send scrambled mpeg
packets through to the filter graph? Or does it mean that it only sends
the current TV station stream through to the filter graph?

I'd guess it depends on the actual implementation... The better definition
for what I meant with hw-demux should be "hw-packet-filter" - it shouldn't
care about the contents of single packets at all - the more "high-level" the
functions of the demuxer get (e.g. attaching time-stamps to samples,
rebuilding complete pes-packets...) the more likely they will fail, since
informations of the _descrambled_ stream are needed for this kind of
operation.
If your hw-device tries to perform such high-level operations, it will most
likely discard all packets it can't understand (because they're scrambled) -
if it simply outputs packets with pid x on pin x and packets with pid y on
pin y then it should work.

May I ask what kind of device/card you have that you think performs
hw-mpeg2-decoding?

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).

So how would this work with DirectShow? A filter graph consisting of a
source filer (a BDA-hw-mpeg-capture-filter) which outputs decompressed
video and audio data ready for rendering and a video sink and an audio
sink?

Most likely this is implemented with no graph at all (e.g. technotrend
dvb-s _premium_ only exposes a custom sdk, no bda-drivers).
If anything at all, it would work with some kind of overlay-surface (where
the decoded video-frames get copied to the graphics-card directly) - I
personally have never seen a bda-capture-filter output pin with anything but
a full (or partial) mpeg2-ts - any decoded output-pin would present a
_massive_ load on the system, since you constantly would have to transfer
768x576x24Bitx25fps = 32MB/s from your pci-card or usb-device... If at all
it can only work by using direct-memory transfer to the graphics-card. Then
the components of the graph should be "wrapped" in dummy directshow-filters,
presenting a "regular" graph to the system, but the actual samples (bytes)
never leave the card - with such a graph you also won't be able to insert
the sample-grabber or a custom-transform filter into the graph.
--
Peter Feldbaumer
p dot feldbaumer at utanet dot at


.

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