delinterlacing 101

[stevech]

noob

If my PC with SageTV has an S-video out - and no mpeg decoder hardware, does my decoder (SageTV or other) deinterlace for the PC video card then "re-interlace" for the video-out jack? The video-out was intended to make the 800 x 600 mode of my PC video card NTSC compatible, so that led me to think that it was re-interlacing. That is, does mpeg as in SageTV's recoder yield an interlaced recording file?

And maybe this is why my SageTV recordings look very much inferior to Standard TV picture quality (missing high-frequencies - looks "soft").

Sure wish I could fix thisl. I've tried the three decoders that come with Sage and fiddled a bit with settings. Same problem on two PCs I've tried. I assume 800 x 600 is the optimum mode.

[stanger89]

You got it. In your setup, video is deinterlaced, scaled to 800x600p, and then scan-converted back down to 720x480i.

[stevech]

Is there a way I can reduce the machinations to improve the final quality?
I suspect not, from what I gather here, no matter what modes my video card has. That is, 720x480 mode of my video card wouldn't help much.
I assume that the de-interlacing software does NOT discard half the lines (one field).

would a '350 or other board with hardware decoder greatly (GREATLY) improve things?

Because of the on-screen-menus issues with the '350, I've avoided it - hopefully I'm not mistaken about this.

[davin]

I'm running 640x480 resolution into my SDTV with the s-video input, and the picture quality looks very good. I'm using a mobo with a Geforce 6150 chipset and the PureVideo decoders, and I record on DVD standard play quality (3.2 gb/hr). Make sure that your bitrate is high enough... the poor quality could be due to that as well as your 800x600 resolution.

[dflachbart]

Originally Posted by stevech

That is, does mpeg as in SageTV's recoder yield an interlaced recording file?

Originally Posted by stanger89

You got it.

Mhh, now I am confused. I always thought SageTV files are non-interlaced, and that the recording is re-interlaced for the TV-out on playback ...
Am I wrong ?


Dirk

[nielm]

* STDV is interlaced -- ie broadcast as 2 half-frames, one following the other

* PVR-xxx cards encode each half frame separately, generating an interlaced MPEG2 stream with the 2 half-frames following each other in the stream.

* MPEG2 decoders can output an interlaced stream (to allow deinterlacing with something like ffdshow, or dscaler), or can usually perform some basic de-interlacing internally (see the mpeg2 decoder preferences)

* The windows desktop is NOT interlaced, so deinterlacing has to be done when displaying the video. It will also be scaled to fit the window by the renderer


If you are using S-Video SDTV TV-out, then this is an interlaced signal, so the video card takes the progressive desktop and re-scales to x480 and generates interlaced frames for the SDTV to display.

The video card often has a 'flicker filter' for TV-out. This basically blurs the desktop to avoid there a no single pixel lines which only appear in a single interlaced frame. For Sage, it is often best to turn this off, as all it will do is blur the video.

[dflachbart]

Thanks for taking the time to make this clear.

One last question, then I'll shut up :

so if the Sage file is interlaced, and I play this file back via S-video out to my (obviously interlaced) standard TV, will the decoder perform no additional interlacing/deinterlacing at all, since the stream is already in the correct format ?

In other words: I understand that VGA-out is non-interlaced, and s-video is interlaced, but I'm not quite sure how the decoder deals with it. De-interlace the file for the VGA-desktop, and then re-interlace back for the s-video out, or omit these two steps altogether for the s-video out ?

Dirk

[dflachbart]

Originally Posted by nielm

If you are using S-Video SDTV TV-out, then this is an interlaced signal, so the video card takes the progressive desktop and re-scales to x480 and generates interlaced frames for the SDTV to display.

Never mind, I should just read carefully before posting. I guess you already answered my question above - the signal will be de-interlaced by the decoder and re-interlaced by the video card.



Dirk