Date: Fri, 3 Apr 1998 10:34:27 -0800 (PST) From: Hugh LaMaster <lamaster@george.arc.nasa.gov> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: multimedia@FreeBSD.ORG Subject: Re: advice sought on new ioctl for frame grabber. Message-ID: <Pine.SOL.3.91.980403095529.22803A-100000@george.arc.nasa.gov> In-Reply-To: <199804031614.SAA28236@labinfo.iet.unipi.it>
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On Fri, 3 Apr 1998, Luigi Rizzo wrote: > Looking at the IETF (nice) and INFOCOM (ugly) (*) video multicast > these days, I was thinking of what could be a nice feature for the : I guess you would want to modify both the driver and vic in order to achieve lower CPU usage and optimize bandwidth effectiveness. I assume that you are trying to send a sequence of stills most efficiently. You can sort of do that now, although not as explicitly and efficiently as I assume that you would like. > (*) why do i think the INFOCOM transmission was ugly ? For the : > Audio had similar problems in that they were sending short (probably > 20ms) frames instead of the more effective DVI4 (80ms frames, 32KB/s) used > for IETF transmissions. Agreed. Presentations/lectures work fine using /4, and they use less bandwidth. DVI/4 is probably the best compromise. I'm not sure why people seem to be reluctant to use /4 instead of /2, and the lower "quality" of DVI is offset by the lower bandwidth, permitting *higher* quality over ISDN. The combined difference (pcm2 -> dvi4) is 71Kb/s -> 36Kb/s. I suspect one of INFOCOM's problems was that INFOCOM was using ICAST Broadcaster V2.2 on either W95 or NT. In particular, when someone accidentally started to send significant back-traffic (another video), the audio quality declined dramatically, so the incoming traffic seemed to cause a problem. I don't know if the problem is the ICAST product, W95 or NT (I don't know which they used), or, if the PC they used wasn't fast enough. -- Hugh LaMaster, M/S 233-21, ASCII Email: hlamaster@mail.arc.nasa.gov NASA Ames Research Center Or: lamaster@george.arc.nasa.gov Moffett Field, CA 94035-1000 No Junkmail: USC 18 section 2701 Phone: 650/604-1056 Disclaimer: Unofficial, personal *opinion*. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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