Interlaced playback from PC

[Floatingshed]

My S3 graphics card in my home-made media centre plays back interlaced avi's (xvid) very nicely provided that I use the Divx codec for playback. If I switch to Xvid (my preference) or even use ffdshow the result is deinterlaced.
Can anyone give me any idea where to start an investigation into what is going on please?

[namaiki]

in ffdshow, make sure that deinterlacing is enabled. Also, find out where/when divx codec is performing deinterlacing.

[Floatingshed]

Why would I want to enable deinterlacing? I want interlaced playback...

[kieranrk]

Why do you want interlaced playback?

The deinterlacing performed by your graphics card is almost certainly superior to anything on your television.

[Floatingshed]

I want interlaced output because I want to watch interlaced material, on my interlaced TV.

I really don't understand why everbody is so obsessed with de-interlacing everything. If it was made interlaced that's how it should remain. Why throw half of it away for no reason?

[kieranrk]

Then just use a deinterlacer that has bobbing support so you don't lose temporal information. Most screens these days are progressive so it has to be deinterlaced.

Though in your case it makes sense to leave it if your tv is natively interlaced.

[pie1394]

For interlaced contents which has vertical scaling at output to interlaced output device, if the deinterlacing process is not performed, the vertical scaling algorithm HAS to be the "field scaling" approach.
Ex:

SDTV 480i --> HDTV 1080i

Even field 240 lines --> 540 lines
Odd field 240 lines --> 540 lines

Scaled Even and Odd field images are still not displayed at the same temporal timing.

On the other hand...
If the down-scaling factor is 0.5x or smaller, the deinterlacing process can be waived.

[pandy]

Maybe set proper ie interlaced graphic mode on your card? for NVidia cards such mode can be created (personally i made few native interlaced modes for my monitors - also TV formats are workable)

[Ghitulescu]

I want interlaced output because I want to watch interlaced material, on my interlaced TV.

I really don't understand why everbody is so obsessed with de-interlacing everything. If it was made interlaced that's how it should remain. Why throw half of it away for no reason?

Finally some one else (than me) :p

It's difficult to find a graphic card that [natively] works interlaced, as no PC monitor ever was interlaced. The only workable solution I know is to use an interlaced-aware software (like Premiere) and to play the video from its timeline using a capturing card that of course feature video out.