[mythtv] Thoughts on encoder farms / distributed capturing and viewing

Robert Middleswarth mythtv-dev@snowman.net
Fri, 01 Nov 2002 16:52:37 -0500

Craig McLaughlin wrote:

>On Wed, 2002-10-30 at 22:29, Robert Middleswarth wrote:
>>You are right that 1 Well Comprised Video Signal could be sent from a 
>>Video Sever to a Video client without to much trouble. but we aren't 
>>talking about that.  We are talking about multipule pc talking back and 
>>forth.  So 1 PC could be asked to Xfer Saved data and Xfer Live Data and 
>>Receive Live Data using a Codec that was designed for speed not size. 
>> Althought we are talking about 100 based network cards they do start to 
>>slow down in the 3-4 Meg range.  Granted if you are talking about 1 
>>Machine for Encodeing and 1 Machine that only displayed then yes there 
>>would be no problem but that isn't what Mythtv is doing at this time and 
>>if I read right not what  Robert Kulagowski was talking about.
>100Mbps NICs slow down in the 3-4 Meg range?  What kind of environment
>have you seen *that* in?  I've seen that kind of poor performance on
>some older machines running Win9x, but my little pentium 166 firewall is
>routinely asked to push upward of 30, and handles it just fine...  I
>suspect you may be seeing IP stack issues and not hardware issues...
>I regularly toss very large datasets around my network here, and often 
>saturate my 100Mbps switch without too much trouble (note: my 100Mbps
>switch is actually a cheapo one that only has a 200Mbps backplane).
I just tried this at home I xfer 3 7??M files from a Redhat 7.3 Box to a 
Redhat 8.0 Box and my Xfer rates were 5mb accroding to the FTP Client.  
NFS might be faster then FTP but still the max I am getting is 5mb over 
my cheapo switch and intel / reltek 8139 cards.

If you use the rtjpeg codex which produces files optmized for Speed not 
size you aren't going to be able to do more then 2 streams.  If I am 
rembering correctly I have seen number for 2.5 to 3.33 megs for MPEG4 so 
if you say only 3 Megs for rtjpeg and say get around 6 Megs can be 
xfered then 2 Stream would work fine but more then that would require 
some form of load balancing multi-nic card.  If I screwed up the number 
some place let me known as conversion between Bytes and Bits get 
confusing and could make my number off by a factor of 8.

After running that test I was think there might be some limits based on 
HD Speed and I think both machines have DMA off so that could be 
improved.  However I doubt it will go from 5 to 30.