[linux-dvb] Re: Generating progressive video

[Michael Hunold <hunold@convergence.de>]

Hello Michael,

On 02/16/04 23:38, Michael Plagge wrote:
> On Mon, 2004-02-16 at 21:45, Juha Pahkala wrote:
>
> > Allow me to suggest something (hopefully not too stupid)
> >
> > Why not make this part of the 'softmpeg' library announced in
> > direcrfb.org site a few weeks back. There is already CLE266 based
> > hardware decoding being developed there in addition to software decoding
> > I believe, so adding av7110 based hardware decoding there also might
> > make this softmpeg library quite useful for lots of projects.
> i am not quite sure if i get your point. I just read the info about this 'softmpeg'
> library. If understand the infos right, this library aims to provide on
> the one hand a software layer for decoding mpeg2 and on the other hand
> use the hardware mpeg decoder CL266 on VIA boards. This decoder seems to
> be hardwired with the TV-out of the VIA-boards. 
This is not right. The decoder is an independent piece of hardware. It 
can be used like the libavcodec software mpeg decoder, ie. you give it 
an mpeg stream and it decompresses (not displayes!) it to some memory.

If you have a cle266 based board, all libavcodec call should be 
substituted with calls to the hw mpeg decoder.

"libsoftmpeg" will never use the mpeg decoder inside the popular 
full-featured dvb cards (see below).

> My intention is to provide (hopefully) a software which put deinterlaced
> video material via a digital connection (DVI) to appropriate TV or
> beamers. The main difference to the softmpeg-library is the focus on
> generating high quality deinterlaced progressive material. I am not sure
> if the CLE266 hardware decoder is capable of providing progressive
> output ?
I think it is -- but I need to get this confirmed by a colleague.

Anyway, what solution (ie. which gfx adapter) do you have in mind to put 
the result to your beamer via DVI?

> Do you think these different aims could be reasonable combined ?
If you really want to get the highest possible video quality, then you 
should forget about using a full-featured card.

The problem is, that there is digital => analog => digital conversion 
inside the card: the av7110 decodes the mpeg stream and outputs an 
analog signal to both it's tv out and to the saa7146. The saa7146 
digitizes the signal again and the busmasters it your PC via 
Video4Linux. In theory this conversion could be lossless, but to give 
the user an acceptable visual experience on it's PC, the picture is 
cropped (to get rid of unacceptable stuff that normally is in the 
overscan area of your PC) and slightly resized.

For the best visual experience, on a non-cle266 system IMHO it would be 
best to use CPU horsepower and "libsoftmpeg" and add deinterlacing 
algorithms before the picture is blitted.

If you use sophisticated deinterlacing algorithms, the few CPU cycles 
burned for mpeg decoding don't matter that much IMHO.

What do you think?

> sincerely
> michal 
CU
Michael.


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