[AG-TECH] Have we looked at vBrick?
Markus.Buchhorn at anu.edu.au
Tue May 22 20:20:52 CDT 2001
At 02:20 PM 22/05/2001 -0500, Robert Olson wrote:
>At 02:11 PM 5/22/2001 -0500, Bill Nickless wrote:
>>Remind me: what's the problem with converting to mpeg-2? Is it the
>>encode problem (expensive) or the fact that mpeg-2 decode is more
>>expensive than h.261 decode
>Price and availability of robust encoders for one. There are latency
>issues (need to be able to tune the encoder to not do the prediction
>mechansim that requires a second of buffering to decode) as well; there's
>not a widely available MPEG2 over RTP library that I know of as well.
Encoding is CPU-expensive, decoding is reasonably CPU expensive. Latency,
as Bob mentions, is a hassle, even with the hardware encoder cards unless
you can convince it to do pure I-frames (i.e. intra-frame compression only,
or at least back-deltas only), but you pay in bandwidth.
I have found one mpeg/rtp piece of code (linuxtv.org), and it is pretty
trivial (and not quite to rfc2250 spec) - it just divides the mpeg stream
into 188 byte payloads and shunts them off. No frame boundary alignment or
other rfc2250 "required/recommended" bits. But it seems to work from what I
have heard. I'm trying to get somebody here to do it properly, I just
haven't found the right bribe yet :-)
>WinTV + H261 might not be the best, but you can't yet beat the price and
Yep, and it does perform remarkably well.
I have some new cards here that I'm just starting to play with. "Realtime"
(we'll see) MPEG2 encoder for under $US1k, decoder for under $US100.
Neither card does RTP streaming/receiving, but I'm working on that...
Still, there is a rapidly growing market now that you can get MPEG2 on
(almost?) one chip.
MPEG1 would be a nice intermediate option, since you can go to decent
PAL/NTSC resolution at 30fps within 1.5Mb/s. The h.261 codecs are CIF
(320x240?), right? and (are designed to) run well under 1.5Mb/s. (it's
N*64kb/s to support the ISDN world)
At the lower end, is anybody doing something with H.263 (very low
bandwidth)? It's a big area of interest now, as MPEG-4 uses it, and the
PDA/cell-phone companies are very keen on it.
Conversely, some UWash/Stanford guys are playing with realtime HDTV (40Mb/s
at tolerable latency, 270Mb/s for pure I-frame low-latency :-) ).
Point-to-point only so far that I am aware of. There's also an
internet-draft for raw HDTV over RTP(modified) - 1.48Gb/s :-) Plus I know
NEC make some big (3 gun) projectors that have 2500x2000 display space
How flexible is the AG setup to putting in other codecs or indeed other
Markus Buchhorn, Faculty of Engineering and IT, | Ph: +61 2 61258810
email: markus.buchhorn at anu.edu.au, mail: CSIT Bldg #108 |Fax: +61 2 61259805
Australian National University, Canberra 0200, Australia |Mobile: 0417 281429
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