brad+myth at templetons.com
Wed Aug 2 07:27:03 UTC 2006
On Tue, Aug 01, 2006 at 09:53:44PM -0400, Michael T. Dean wrote:
> Heh. 720x480 @ 30 frames/sec (60 fields/sec) takes 15MiB/sec (yes,
> that's a capital B as in 15,552,000 bytes/sec) at 12-bit color (and no,
> that's not 12 bits/color/pixel, that's 4 bits/color/pixel). Therefore,
> uncompressed SDTV takes 124416000 bits/sec = 124Mbps. Yes, that's more
> than 6 times the maximal bitrate (i.e. 19.39Mbps) of (most) HDTV
> (ignoring the 38.78Mbps of high-data-rate mode, that you won't see for
> terrestrial broadcast). So, really for transmission across the network,
> "even" SDTV must be compressed. (Imagine that MPEG-2 can get that same
> 124Mbps down to 2.2Mbps with pretty good quality and 4.4Mbps with good
> quality. Now that's compression.)
There isn't really 720x480 in an NTSC signal. You will do fine with
480x480, and you will also do fine with YUV encoding at 16 to 18 bits
per pixel, which means around 14 megabytes/second, which is intense,
but doable over gigE. Which I guess they didn't support.
But I do agree, a compression chip -- whatever's cheapest even mjpeg,
but mp2 is getting quite cheap -- is the right idea.
Based the pvr-500 being down to $140, those chips are getting less,
but I think they may be right to start with the lower price point. If
it had to be $250 with 2xatsc, 2xntsc, people would start to balk.
Of course, as a plus, as the "standard" comptuer starts having a good enough
video card, this box (or a similar one on USB-2 which at 400mbits could also
do the uncompressed capture) starts becoming "all you need" to put on your
network to turn all your *nix boxes into PVRs.
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