Re: Compression Codecs

Jay_Feldis@logitech.com
27 Apr 95 14:56


[Text item: Re: Compression Codecs]
OriginalPath:
My undersatnding is that MPEG (1 and 2) is targeted at storing and
retrieving video in a highly compressed format (ie- for video on demand),
minimizing transmission delays is not the focus. "Real-Time" means that
it can accept data input at live speeds (30fps?), but does not
necessarily address the issue of transmission delay. MPEG must look at
several frames forward in time to calculate the compression vectors, this
means that the codec must hold several frames at one time before
compressing and transmitting, resulting in a delay of several frames from
the time the video was recorded by the camera to the time is is
transmitted. We would perceive this as a noticable (and annoying) lag
between the parties in a two-way converation.

There may be MPEG based schemes that have less delay, but these will not
have the same tremendous compression rations. This is why H.320 has been
developed and is in use by the VideoConferencing leaders such as
PictureTel and CLI.

How much is "affordable"? What do these codec chips cost?

/Jay

-----------------------

One thing though, what I've been trying to say is that MPEG-2
does the ENCODING/Decoding in REAL TIME...that fast...using ONE CHIP for
ENCODING and one CHIP for Decoding...RISC based chips..at about 50 MHz ..
In my opininion, this kinda of speed IS good for videoteleconferencing...

On 27 Apr 1995 Jay_Feldis@logitech.com wrote:
>
> [Text item: Compression Codecs]
> OriginalPath:
> I am also interested to know if CUseeMe will employ any kind of video
> compression. I would think this would help reduce bandwidth and/or
> increase frame rate.
>
> I think that MPEG is not really suitable for real-time live video
> however, becasue it works by looking at several frames at once and then
> generating vectors to represent the changes to the image over a period of
> time. As a result, you must store these frames long enough to do the
> compression which would cause a significant delay in the transmitted
> signal.
>
> The emerging video conferencing standard for ISDN telephone connections
> is ITU standard H.320. This is used by PictureTel and Vivo and many
> others. I don't know if this can be used via PPP connection however.
>
> There are a number of simpler compression algorithms that can give you
> 4:1 compression or so (executed in SW), this might not be too hard to
> implement.
>
> /Jay
>
>
> Did ya guys read "Multimedia Today".... the article "MPGEG-2: New
> World Standard for Digital Video"???????
> WOW up to 200:1 compression!!!!!!!!!!!!!!!!!!!!
> 30:1 at TV quality....of course CD sound quality....
> BACKWARD COMPATIBle with MPEG-!...
> HEY YOU GOOD PEople at cuseeme DEvelopment, What do you think? can you
> write something compatible with that codec?
> For more information here's a number 180-IBM-0181, ext. 1502 or send an
> email to JOHN G. Stamm at JSTAMM@vnet.ibm.com
>
> CHILLS GOING UP MY SPINE!!! Exciting Stuff!
> DisplaySubject: Compression Codecs
>
DisplaySubject: Re: Compression Codecs