[AG-TECH] PPT in a vic window

[Markus Buchhorn]

At 10:15 AM 15/01/2003 -0700, Don Morton wrote:
>Has anybody looked at the possibility of just feeding something
>like a ppt or vnc session into a video stream that would
>pop up as a thumbnail with the rest of the videos? 

Frequently - and it ain't real pleasant, depending on the content. You can use a scan converter to change XGA to PAL/NTSC video (off the shelf, a few hundred dollars/pounds, or there are some circuits around for building your own) and feed that as a video signal to your encoder. These are also used for putting your PC output on a TV, same idea. You can also (somehow) use a screengrabber under vic (works for XWindows, not sure how you do it under MS-Windows) to just encode a piece of screen real-estate. Or just point a camera at the projected screen/monitor (you'll need a genlock to synch the camera with the display to avoid the black bars). H.320/323 users have been doing this for ages.

However, you're taking a (typically) 1024x768 image, binning it down to PAL/NTSC (~55% of the data is gone) then binning it down to CIF (~75% loss from PAL/NTSC there) and finally compressing it with a lossy codec like h.261 and putting it onto a lossy network. So it really depends on your content. 

It's doable, and can work well if the content is appropriately designed, and it properly supports arbitrary applications and embedded animations/videos/etc. 

You can also crank up the 'quality' of the h.261 codec, to reduce its "lossiness" (like jpeg's Q value), or perhaps look at other codecs (h.263/mpeg4 or mjpeg or ...) to give you higher resolution recreation of the original. As long as your receiving sites support it... You can usually tradeoff bandwidth against framerate, so it still comes out at a 'normal' rate.

Cheers,
        Markus


Markus Buchhorn, ANU Internet Futures Project,        | Ph: +61 2 61258810
Markus.Buchhorn at anu.edu.au, mail: Bldg #108 - CS&IT   |Fax: +61 2 61259805
Australian National University, Canberra 0200, Aust.  |Mobile: 0417 281429