[ILUG] Streaming video

[Niall O Broin]

On 21 Sep 2005, at 09:40, Paul Jakma wrote:

> On Wed, 21 Sep 2005, Niall O Broin wrote:
>
>> 150KB/s. And anyway, testing shows that on a straight copy, I'm 
>> getting ~ 500 KB/s over the wireless LAN and 2-3MB/s on the wired 
>> (which is also crap, but should be more than enough)
>
> So what are the differences between your 'straight copy' case and the 
> poor performance case? (application? number of clients? protocol?)

The straight copy figures were to show that the throughput over the LAN 
(wireless or wired) should IME be well more than enough for the video, 
but yet it's not playing correctly. The video amounts to about 150KB/s. 
It has been suggested to me that the problem is related to the sound 
and video streams being mixed in the video, and having to be remixed 
appropriately on the client, and I know squat about the avi file 
formats, so can't comment. But surely the audio and video streams must 
be somehow interleaved in the file anyway?

>> Neither am I TBH but AIUI real world throughput on wireless LANs is 
>> only about 50% of "wire" speed,
>
> Throughput of 50% compared to baud-rate at *best*.

So getting 500KB/s from an 11 Mb/s WiFi connection is about as good as 
it gets, which is fine - and I would have thought that it SHOULD be 
enough.

> Have you tried measuring latency, particularly while you see this poor 
> performance in this 'streaming' thingy?

TBH I don't see how ANY kind of latency issues can explain the client 
pausing for periods of seconds. But I just ran a ping while a file was 
playing and the numbers were all over the place:

round-trip min/avg/max = 2.338/24.881/193.09 ms

while without a file playing, the numbers were also all over the place, 
but not QUITE as bad:

round-trip min/avg/max = 2.262/3.67/53.916 ms

So, what the hell is causing that - a dodgy AP (mine is a DLink 
DI-614+) ?  And even with those numbers, how are pauses of seconds 
explained?

One part of the answer may be OS-X - it seems that copying a file over 
the network hits its CPU hard, for whatever reason. I have a little CPU 
meter thingie in the menu bar, and I noticed that it was pegged when I 
was copying a file. I then copied a file running top, and I was getting 
 > 50% sys CPU usage, which seems odd. Wondering was it related to SMB, 
I then exported the filesystem with NFS and that seems a little better. 
CPU usgae is again high during a copy, but video playback over wireless 
is a lot better, though still not perfect. Video playback over NFS over 
wired seems to have no problems at all.

Bloody computers :-)



Niall