VidCap vs Quickcam FPS debate continued

Dale Paul (dpaul@sierra.net)
Sun, 11 Jan 1998 15:43:59 -0800


Ok..new to this list...but I see alot of debate going on about VidCap Cards
vs. QuickCam vs. MJPEG vs. CU-SeeMe Gray etc etc.....
It's just too bad alot of the responses to this list that I have seen have
been "I dunno"..."Never heard that before"...etc etc...
Talking about wasted server bandwidth...I would rather hit the delete button
on an unwanted attachment than have my mailbox, or to see the list server,
cluttered with that. Oh what some people wont do to see their name in lights
<G> Oh well..my two cents.....
FYI..since this is NOT an attachment, MIGHT be under 20k...it is in one
piece...so hit the delete button now if you don't want to read it :)

For a very good source of information on WHAT a codec is and how they all
stack up....this URL is pretty good:
http://www.terran-int.com/CodecCentral/

Now for my nickle.... and to join the battle as a new recruit ...
Of all the debate here, on whether you should be moving or sitting still for
the best frame rates, can best be understood on how the Video Codecs work.
In a semi-nutshell....BOTH Color and Gray codecs break your picture up from
little itty bitty pixels into larger squares, before it starts to work on
it. (Much like the heavy lines on graph paper). Leaving it there (and
letting you read the URL if you want more) this algorithm actually ADDS
overhead to the video as a general rule. That is to say...if every pixel in
the box is different, the results can be larger. Now heres the good part :)
In Color..the human eye is less sensitive to Blue and other little
subtleties, so if your vid quality is set low, the codec can start to
"smear" pixels and throw out those parts that the human eye is not gonna see
anyway...so it can make all those "unlike" pixels more "like" to acheive a
better compression. The B&W codec does not smear pixels nor doe it compress
pixels. It takes the current image and subtracts that from the previous
image. This is known as video differencing. So now, only those little blocks
that have changed are sent on (In MJPEG, EVERY frame of video must be sent.
This is why Color Vids do not suffer from the "pixel" effect that we are so
use to seeing). So...the things you can do on YOUR end to help acheive good
frame rates are:
1) If in color, lower your quality. It does not take much quality in CU for
someone to get the point :) This allows the Color Codecs to make more "like"
pixels for you and acheive higher compression rate.
2) Both B&W and Color.
a) Use a less busy background. A single color (dark), static (not moving)
background works well.
b) You don't need to sit still .. but avoid doing the macerena on your cam,
as this makes for LARGE packets :)
c) Dark is good! Black bits are zero...they compress REAL WELL. But..we all
don't need to look like Johnny Cash :)
3) Enable Compression on your modem! While this does not help packets on the
internet backbone...it can sure help you get more outta your modem to your
ISP. MJPEG is already compressed but B&W users can benefit from the added
hardware help.

Now for Quickcam vs. VidCap card.
This is a case where living in a world of "Standards" and "Abstracts"
actually hurts. Those with VidCap cards probably have a little chip in there
that is sitting dormant that is perfectly capable of doing our Video
Compression for us. But alas...Video for Windows and Quicktime say everyone
has to live in their own little box. So now we have separate Drivers and
Codecs for working with video/audio. :(
I'll spare everyone the engineering calculations and count of CPU clock
cycles on this one..but in a nutshell....the quickcam driver is required to
POLL the parallel port for the video, where a capture card has those nifty
little chips on it, does that for us. In my estimate, the VidCap card saves
*my* CPU from having to read aproximately 30,000 bytes of data every second
from the parallel port. In the overall scheme of things, this is not
much...but hey..since I got my VidCap card I now have a few CPU cycles left
for Solitaire :)

The Imperfect World of UDP and BandWidth:
Now for those who do not know this, CU-SeeMe works by using the UDP
protocol. For the laymen, this is SCUD missle technology. Your video is
pointed at a target, fired, then forgotten about. You aren't even gaurenteed
that it will reach it's target. This works both ways, from you to the
Reflector and vice versa. Lets assume for sake of argument that the server
is on a high speed internet backbone with plenty of bandwidth to receive the
MAXIMUM packets from all 25 participants. Ok..so far so good...except here I
sit on my 28.8 modem....on an oversold ISP..competing with AOL for bandwidth
on the SprintNet backbone.....with a 250millisecond delay per hop with over
15 hops to the Reflector...ack..(so much for Real Time Video hehe).
I like to keep little Cindy eating her oreo's vid open all the time (along
with the other 25 participants) ...and because I like CU...and for no other
reason other than I can..open 7 other video windows. Now the server is
trying to send me ..oh...5 frames for each user....thru 15 hops with a
latency of around 15 minutes (exagerated) but alas..my modem chokes and my
local router succesfully drops 80% of those frames. On a rare occasion
(2.1.1 user here) my Computer suffers a Myocardial Infarction and Blue
Screens on me when things get real bad (result of "standards" and too many
"abstracts"..not WP's fault). So now I sit....can't see Cindy eating the
oreo or for that matter anything else. I have dropped all the "key"
frames...difference frames etc and the world looks like Picasso to me. So I
have grown older and wiser and don't need to look at John smoking a
cigarette anymore. Now I only watch little Cindy eating her oreo and life is
good (well...better anyways). (psst..Cindy also has a dark background so vid
moves good).

So the moral of this story is...keep your video simple....open what YOU
need....don't show off your Cable Modem because its only gonna get thrown
away to the modem users anyway, and CHECK your max/min SEND and RECEIVE
rates (aimed at all the 3.1 WP "CU_SeeMe User" users using LAN settings
instead of modem settings..Thank you White Pine for making the Reflector
Monitors job so easy..was almost getting bored there hehe).