Date: Tue, 16 Sep 1997 13:04:36 -0700 (PDT) From: lamaster@george.arc.nasa.gov To: multimedia@FreeBSD.ORG Cc: luigi@labinfo.iet.unipi.it Subject: Re: X11 video grabber for vic... Message-ID: <199709162004.NAA00339@george.arc.nasa.gov>
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luigi@labinfo.iet.unipi.it wrote: > right now I am following the sigcomm session which is being > transmitted with vat&vic ... I must say that I am _not_ impressed > since 99% of the times vic is used to show slides and there is all > kind of artifacts in acquiring slides using the camera. Much better > results, at a fraction of the bandwidth, could be achieved by using > an X11 grabber as it was available in nv. If I understand your criticism of the broadcast, vic actually already contains the necessary functionality to do this properly. The video operator may need to stop and consider what needs to be done in light of having to work with viewgraphs. Now, vic does have a "sending slides" option, and I'm not actually sure what it does. A cursory view of the documentation doesn't say, and it isn't obvious to me from switching it off and on. OTOH, all it takes to transmit slides properly using H.261 is to reduce the framerate (to, e.g. 1 fps) and increase the quality (to, e.g. 1). Of course, the operator has to adjust these as the video changes from speaker to slides and back again, since 1 fps isn't a very interesting way to watch someone speak and move. And, of course, the best solution is to use wb to transmit the slides, (or, for small audiences, web pages - but, I like wb/multicast) and use the video for the speaker. But that presupposes that the slides have been prepared in advance... Nobody is satisfied with a video camera pointed at a viewgraph projector, but, since Mbone is usually an afterthought for most conferences, it is difficult to get anything better. But, lack of technology is not the problem here. If the speaker can't give the conference coordinator source, the only option I know of is the camera on the projected images and set the framerate down and the quality up. > Some time ago I started writing an x11 grabber for vic > (http://www.iet.unipi.it/~luigi/grabber-x11.cc), but had to give > up due to my miserable knowledge of X11 and C++ . The code I have > is partly working but it has some rough edges and probably a lot > of bugs and inefficiencies. Do you mean a function that would grab an X11 window as a frozen frame, or a changing series of frames? I sure I'm missing something here, but, is this a totally separate question to the above, or somehow related? I don't remember what nv did, but, if the problem is that the presenter doesn't have computer-available slides to begin with, I don't understand how an X11 grabber will help. What format would the original material be in. Not postscript, or ASCII, or, you would just use wb, and most formats can be converted to postscript. e.g. SGI's "showcase" actually does a pretty good job of formatting its own slides for postscripts. PS slides with images should be handled one at a time and run through "lzps". I think wb is the short-term solution if source material is available. The wb version for FreeBSD seems to work fine. (Better, actually, than wb on the SGI, which still occasionally crashes or hangs or somehow ties up the X server - not that this is criticism of wb. SGI still seems to have display-postscript-related bugs even in Irix 6.2, though not as bad as in Irix 5.2/5.3). > Would someone like to help in cleaning up the above code (which is > partly working) ? Corrections welcome. -Hugh LaMaster Hugh LaMaster, M/S 258-5, ASCII Email: hlamaster@mail.arc.nasa.gov NASA Ames Research Center Or: lamaster@nas.nasa.gov Moffett Field, CA 94035-1000 No Junkmail: USC 18 section 2701 Phone: 415/604-1056 Disclaimer: Unofficial, personal *opinion*.
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