[linux-dvb] Re: OT: a rant regarding DVB-C cards

[Michael Hunold <hunold-ml@web.de>]

Hello Juha,

> The first question that I've been wondering
> is whether to buy a full featured card or a budget one.
> The problem I see with full featured cards is the fact that
> using them you can only output mpeg streams and osd stuff to
> the television.

If you don't want to do on-the-fly transcoding, then this is true.

> I do know that lots of different plugins exsist
> to do various things in the OSD but I really would like to be
> able to for example play 3d games with the same machine that
> is connected to the TV.

But I assume that you don't want to play these games on your tv, right?

> The cpu requierment to do mpeg2 decoding
> in software is the common argument I've seen against a setup I've
> just proposed. But if I'm not mistaken, it's still less than
> transcoding a mpeg4 stream to mpeg1 and feeding it to the full
> featured card in order to play mpeg4 movies on the machine, which
> I intend to do anyhow, so some cpu power is needed nevertheless.

Ok, so CPU cycles is not a problem for you.

> I still think I'll buy a full featured card for now (I think I'll
> end up buying more than one card anyway) since you can't really use
> VDR with a budget card + videocard combination [1],[2] at the moment.
> Please somebody prove me wrong here.

> [1] no, I don't own a dxr3 card and neither do I intend to get one

If you omit the costs, then your thougths are perfectly valid. The DVB 
cards give an excellent picture aswell. But the budget-card + dxr3 
solution would save you a few euros.

> [2] I know of at least one project that tries to accomplish something 
> like a budget+videocard combination, namely
> http://df-gp.sourceforge.net , but I don't know if in development
> anymore

With that solution, it would be possible to use the tv-out of a Matrox 
G400 card, too. But that is very far in the future unfortunately. At the 
moment, this stuff is only in DirectFB, so you need DirectFB aware programs.

Perhaps somebody writes a VDR directfb plugin someday?

> One thing I'd like to know is
> whether I'll be able to use only the tuner part of a full featured
> card in the future, if at some point it'll be feasible to use a
> videocard to output to TV.

In theory, yes. Although all data will always go through the ARM on the 
full featured card and I don't know if this has an impact on the data.

Perhaps when receptions is bad, then ARM crashes are more likely.

That's the reason, why people like "emard" have modified their premium 
cards to support a budget-like TS feed, which does not go through the ARM.

> But at least a couple
> of months ago there was some problems with the Siemens card. I'm
> connected to the HTV cable network in Helsinki,
> Finland, and the problems with the Siemens card had something to
> do with HTV's usage of both qam-64 and qam-128 in their network if I
> remember correctly. Have these problems been resolved yet or should
> I just go with the Hauppauge/TT card.

Sorry, I cannot comment on this. 8-(

> Another thing with full featured cards is the capablility to output
> streams in RGB or at least s-video format. Or do they all support only
> composite output?

The video encoder on the board supports a variety of outputs, but for my 
DVB-S, only the composite output is available. I dunno for other cards, 
some of them probably have s-video outputs as well.

But if you don't fear your soldering iron, it should be possible to use 
s-video on every card IMHO.

> And what about the budget cards. Do these cards have the same problems
> as their full featured 'big brothers' respectively? So I guess what
> I'm asking is, is the ARM chip responsible for the mpeg decoding
> basically the only difference between a full featured and a budget
> card?

The budget cards only have the frontend, some glue logic and the 
saa7146. You will get the "raw" unmangled transport stream, so 
everything has to be done in software -- that's why they are so cheap.

> Best regards,
> Juha
If you don't need to play stuff besides MPEG-1/MPEG-2, then perhaps a 
stand-alone set-top-box (for example the dbox or the dreambox) would be 
worth some thoughts?

CU
Michael.




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