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MythTV, Cable and Parallel Digital interface


Established Member
Ok. This is a long complicated one...

I have a Nice homebuild MythTV box with Freeview tuner.
http://www.flickr.com/photos/[email protected]/589511551/
Its housed in a VCR case to hide under the TV unnoticed. It all works well.

I also have a cable receiver and movie channels. I want to record them, but the composite input on the tuner card is very poor when recording. I dont see why i should have high quality digital channels recorded on crappy composite. So i want to modify my digibox to output digital video.

I found an SDI mod for SKY+ boxes and worked out how to get the same parallel mpeg data out of the cable box. The Chip that decodes the mpeg inside the cable box is a conexant Bt861krf. Because its decoding the mpeg for display the data has already been decoded for ppv/subsciption content and is clear mpeg data.

Ok, A little digging turned up the CX2388x chipset.

"The CX23880/CX23882 provides a 27-MHz, 8-bit ITU-R 656 decoded video input
interface to allow a third-party MPEG II decoder or codec to send 4:2:2 data over the
PCI bus to a target video display frame buffer for video overlay. Alternatively, 480-
line progressive scan video from the CX23490 All-Format MPEG II decoder can be
input to this port using Video Interface Port (VIP) 2.0-compliant pixel timing at up to
54 MHz."

It seems this is used on a LOT of cheap capture cards in the PC.
My plan is to get a cheap card (DVB-T/S) and cut the traces leading from the tuner and connect a 25pin parallel port to them.
In the Cable box ill add the connections (not cut!) on the decoder chip and bring them out to a similar port.
Ill use a VERY short high quality cable to connect the two, and voila! I should get the digital video feed directly from my cable box appearing on the tuner in the PC.
A couple of problems around getting the card to beleive its tuned in so it shows the video, but im sure that can be worked out. It may even be possible to take the tuner controls (often i2c) and interface them to the tuner in the cable box! Thus, turning my cable receiver into a DVB-C decoder with working cardslot :)
My goal here is to be able to record Cable PayPerView and subscription content ( i get freeview easily) in high quality on MythTV. They DO NOT allow cable cards in the UK and even claim its against the law to connect non authorised equipment to the cable network... Bah.

Now, I need to get this to the MythTV box.

What I need is a Tuner card that can accept the Parallel mpeg data ITU 656 format.

to do the actual SDI mod and buy an SDI tuner for Myth will cost about $400, but there is no need if I can get a card that lets me put the PDI straight into the PC.

Can Anybody help?

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