[linux-dvb] Re: Generating progressive video

[Michael Plagge <plagge@onlinehome.de>]

Hello Michael,

On Tue, 2004-02-17 at 14:35, Michael Hunold wrote:
> Hello Michael,
> 
> On 02/16/04 23:38, Michael Plagge wrote:
> > 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).
> 

I see, so i will never say again the the CLE266 is hardwired to the
TV-out :-)

> > 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?


Especially for this i have bought a matrox G450 with dvi-out since this
is the card which seems to be supported best by DirectFB and other
software using framebuffers (mplayer, xine, etc.). Therefore i want to
use the matrox gfx driver.

> 
> > 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.
> 

The fact the the FF-card performs digital => analog => digital
conversion is totally new for me and also a little bit surprising. It
seems that my initial idea of having a fully digital chain is not so
easy to implement.


> 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.


Do you think it is reasonable to use a DXR3 card for hardware decoding
(as you can see i like the idea of hardware-decoding). The main reason
for preferring hardware-decoding is to circumvent the syncing problems
you are describing in the IDEAS-File in cvs.

As you can see from my comments, i just start playing around with these
problems and maybe i am a little bit naive, but while reading you
comments there was an idea coming into my mind. Do you think it could be
possible, if i do the hole thing (software mpeg decoding and
deinterlacing) in software, to use the movement vectors from mpeg2 for a
motion adaptive deinterlacing algorithm (i hope this idea is not too
silly) 

best wishes
michael plagge




-- 
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.