[AG-TECH] Have we looked at vBrick?

Markus Buchhorn 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 
(around $US10k).

How flexible is the AG setup to putting in other codecs or indeed other 
video tools?


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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