Path: utzoo!mnetor!tmsoft!torsqnt!jarvis.csri.toronto.edu!rutgers!ucsd!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcdj!myers From: myers@hpfcdj.HP.COM (Bob Myers) Newsgroups: comp.graphics Subject: Re: Workstations that can record/play realtime video Message-ID: <17400015@hpfcdj.HP.COM> Date: 15 Nov 89 18:52:31 GMT References: <1593@ndmath.UUCP> Organization: Hewlett Packard -- Fort Collins, CO Lines: 38 >> VHS quality 24 bits x 640 pixels x 480 lines x 30 Hertz x 3600 seconds >> is 100 gigabytes uncompressed. >This would imply that a standard VHS cassette tape has nearly 200 GB of >storage capacity. Your multiplication is OK, but I think that's a little >high, else we would all be using these as mass storage backup devices. >Granted, this signal is stored in analog not digital form in the typical >recorder. The multiplication IS correct, and yes, you would need about 100 GB to store the information as given above in digital form. The joys of analog vs. digital storage - why do you think that no one's come out with a digital video disc yet, but you can get CDs anywhere? Of course, there are some assumptions in the above that aren't quite right - "VHS quality" is a long way from 24 bits/pixel, 640 x 480 resolution - particularly the color information, which is severely bandwidth-limited in basic NTSC, let alone VHS tapes. A more realistic approach might be to see how much storage would be required to store NTSC-encoded video; in other words, simply sample the NTSC output of a VCR (or whatever other video source you choose). Here's a rough attempt, and I'm trying to be conservative throughout. TV channels in the US are 6 MHz wide; now, not all of this space is taken up by video information, but let's assume that the NTSC signal needs to be sampled at 12 MHz. Further, we'll assume that 12 bits/sample is sufficient - actually, good results have been obtained sampling NTSC at 8 bits/sample - and that we want to store an hour of video. This gives: 12 x 10^6 samples/sec x 1.5 bytes/sample x 3600 seconds = 6.48 x 10^10 bytes! Your mileage may vary depending on assumptions, but this is a very realistic estimate of the storage required. Bandwidth is NOT cheap. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers%hpfcla@hplabs.hp.com | sentient life-form on this planet.