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SubjectRe: VHS backups - that's why I'll keep Windows98 on my comp
16-Sep-98 16:18 you wrote:
> On Tue, 15 Sep 1998 03:05:26 -0500 (CDT), Oliver Xymoron said:
>> The spec I gave - 320x200x8 at 15 frames per second - is the resolution of
>> an old Fisher-Price video recorder that recorded on audio tapes. NTSC
>> resolution is nominally ~640x~484x~18bpp(1) at 30 frames per second so my
>> original estimate was allowing for more than a 16x degradation in quality,
>> or looked at another way 16:1 ECC. VHS is bad, but not so bad that that
>> wouldn't work.

> You get a horizontal resolution of about 250-300 in the luma signal when you
> record on VHS. The chroma signal is much worse and isn't worth bothering
> with. To put it another way, the bandwidth of the VHS luma signal is about
> 2.5 MHz so base your figures on that. However, whatever encoding you use
> will obviously have to include the correct horizontal and vertical sync
> signals to avoid confusing the recorder and you will want to avoid the
> head-switching noise which generally occurs during vertical retrace.

> However, I have a feeling that some of the processing used in VCRs has
> the effect of merging adjacent lines somewhat, so you might want to
> trust only every alternate line.

In fact backup on VCR is the only reason why I'll keep Windows98 on my comp
for a very long time. There are drivers for DOS, Windows95/98 & Windows NT 4.0,
but not for Linux and I'm not powerfull enough to write my own... Anyway it's
really cheap: 350Kbytes/sec (PAL/SECAM VCR's only, not NTSC ones) and on 4hr
VHS you could store 4.8Gb of data (with huge amount of error-correction code of
course so raw data stored on VHS is >10Gb). Sometimes cheap chineese VHS
reauires 2-3 tries (performed automatically by this horrible Arwin) to read
information but for last two years and 20+ VHS's seen by me there are was no
data loss...




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