[vdr] Re: Interlacing

["Jörg Knitter" <joerg.knitter@gmx.de>]

> Tony Houghton a écrit :
> > Anyway, I presume the problem with these shows is that they're broadcast
> > interlaced, and surely the reason for that is to match the interlacing
> > on the TV, so deinterlacing shouldn't be necessary if the player could
> > sync the interlacing of the stream to the interlacing of the TV output.
> > This might be a bit tricky with the Voodoo, because the X modeline I
> > have to use with it (see below) is not interlaced, so it must be doing
> > the interlacing in hardware. I haven't worked out whether the software
> > sees it as a 25Hz or 50Hz mode, but I think it's the latter, in which
> > case I suppose it would have to provide the user with an option to force
> > it to sync to even or odd frames IYSWIM.
> > 
> > Does anyone have any thoughts on this?

Hi,

sorry, I don´t see the real point in this discussion. Unfortunately, I can
only tell the problems from the Windows side, so I would also like to know
the situation on Linux.

First of all: If you output a video exactly with 720x576 pixels and use no
deinterlacer or postprocessing, it is theoretically possible make it display
1:1 on the TV set (if the drivers output the image correctly resized i.e.
with overscan area etc). The main problem (at least on Windows): It is not
possible to determine if the upper or the lower field is displayed by the TV
output of the graphics card. 

Additionally, if you play back a video on windows, the clock of the sound
card is taken into reference. The disadvantage: There is stuttering from
time to time on the monitor/tv-out. There are tools that change this
behaviour: Reclock sets the sync on the video output and changes the sound
output frequency on analogue output and inserts or deletes AC3/DTS frames if
the A/V sync is not correct.

So the best solution would be if you had a TV output on your graphics card
that is able to adjust the clock dynamically. ATI and nVidia are said to
have a fixed TV output clock, the Matrox cards are said to have a variable
one.

And in fact: Matrox cards are the only cards I know that enable 1:1 output
on Windows. There is a function called DVDMax that outputs the image
correctly scaled and synced to the TV out. Unfortunately, this software also
can´t determine the field order. This is why you get a field order checkbox
in the drivers where you can say if the video played has to be output upper
field first (e.g. DVB) or lower field first (e.g. DV videos, DV videos
converted to MPEG-2).
If you (still) have a windows partition and a Matrox card, just check it out
by playing a DVD with deinterlacing set to 'weave'.

I think the linux situation might be the same: If something like the DVDMax
option exists in DFB, the Matrox cards might be the only ones that can
output a video perfectly without any necessity of deinterlacing or
post-processing.
For all other solutions, you might have to do it like it is done with the
Windows Media Center Edition: Deinterlace the material to output it to a TV
set making it interlaced again. I like to compare this with compressing an
WAV to MP3 to be able to play it back uncompressed - lot of people would not
see (hear) the quality loss, but it is there and it would be unnecessary if
graphics card design/drivers would be better. Nevertheless, a few years
later, interlaced TV might be the past as we all will have flat screens that
work progressive - so a deinterlacer is always necessary.

With kind regards

Joerg Knitter