[mythtv-users] CPU power and decoding

Jay R. Ashworth jra at baylink.com
Thu Sep 30 14:31:25 EDT 2004

On Thu, Sep 30, 2004 at 02:40:59PM +0200, Milos Prudek wrote:
> I would like to build a MythTV box (frontend/backend in one PC). Are the 
> following sentences true or false?
> - DVB broadcasts in MPEG-2; consequently there is no encoding taking 
> place when saving a DVB broadcast to disc.

Correct.  Or at least, it *can* be correct; there's a possibility that
it might depend on the chosen tuner card.

> - When watching a DVB broadcast, the CPU must decode MPEG-2, or the DVB 
> card's onboard hardware MPEG-2 decoding takes place.

*Something* certainly must decode it, yes; there's a possibility the
DVB card might have an MPEG decoder, and there's an (even smaller)
possibility that there might be a way to access said decoder from

> - When watching an analog TV broadcast, no significant decoding takes 
> place and the burden on the CPU is very light.

If you're bypassing the box, this is true.  If you want to use the
fancy features<tm> of myth WRT live broadcast, then it is not: you will
be simultaneously recording (to the ring buffer, if not to a recording
file) *and* playing back.

> - When recording an analog TV broadcast, the encoding done in software 
> via CPU will consume less than 1GHz of processing power.

This depends on the tuner card as well: hardware MPEG cards like the
Hauppauge, AVer 179 and Yuan do indeed consume little horsepower
because, like the DVB cards, they output precompressed MPEG-2 -- they
do it by having an onboard co-processor that does the hard work,
converting electricty into heat.

> - When watching a DVB broadcast, the decoding done in software via CPU 
> will consume less than 1GHz of processing power.

Can't speak to this one.  Can you software-decode NTSC-rate MPEG2 in a
GHz?  *Maybe*.

> - When buying both a DVB card (the new SkyStar1 CI) and an analog 
> terrestrial TV card, I will need only one remote control (for example 
> the SkyStar's remote control), and I will be able to control the whole 
> MythTV with it, i.e. both the DVB and analog card.


> - It is actually possible to have a wireless IR keyboard, wireless IR 
> mouse and IR remote control, all working, not disrupting each other 
> (equipment recommendations/buying advice welcome).

This depends to a certain amount on the exact devices involved, but if
the IR itself doesn't conflict, nothing else will.

-- jra
Jay R. Ashworth                                                jra at baylink.com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

	"You know: I'm a fan of photosynthesis as much as the next guy,
	but if God merely wanted us to smell the flowers, he wouldn't 
	have invented a 3GHz microprocessor and a 3D graphics board."
					-- Luke Girardi

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