I've recently become interested in ip mulitcast technology as a means of
multimedia transport and i have some questions reguarding the way SGI's
deal with audio/video as opposed to the way windows machines (esp. those
running NT) deal with audio/video, (hereafter reffered to as a/v). My
question stems from the following situation:
I have the following two boxes, both multicasting a/v sessions
(by this i mean to say that they're both receiving audio and video
input, encoding and compressing it, and then shipping the data out
of their respective network interfaces. The video is going out in H.261
format and the audio in PCM format.):
SGI: SGI Indigo2 Impact, 195Mhz MIPS R10000, 128MB, Irix 6.2, running
vic and vat.
NT: Generic, 200Mhz Pentium II, 128MB, NT Server 4.0, Matrox Millenium
video caputure card, running Icast Broadcaster.
The difference in the a/v output quality of these respective boxes is
enormous, with the PC's performance falling far behind that of the
SGI's:
SGI: It's sending the video data out at 128Kbps, 7 frames per second,
and the audio data out at 64Kbps. The a/v quality from these settings
is outstanding.
NT: Using the same 128Kbps/7fps/64Kbps settings as the SGI, the a/v
quality from the NT box is far cry from that of the SGI. I had to push
the video stream up to 384Kbps, set the frames to 10fps, and crank the
audio up to 78Kbps just to get within the same scope of performance as
the sgi?
Questions:
===========
1- Does the SGI do a hardware codec and compression?
2- In general, does a software codec and compression process require
lots of floating point instructions?
3- I noticed that while the vic and vat were broadcasting the audio and
video, there was a process named "videod" that was taking up 60%-70% of
the cpu cycles. What is this process and what does it do? (If it
helps, I was also watching the session on the SGI as i was broadcasting
from it.)
4- Does anyone have any clues as to why the performance difference is so
great? The NT server had no other processes running so it was free to
use virtually all of it's resources on the broadcast processes?
I understand that this a lot and i thank those who've even ventured to
read this far. Please accept my thanks in advance for any help you may
provide.
-tami