[ILUG] Streaming video

[Paul Jakma]

On Wed, 21 Sep 2005, Niall O Broin wrote:

> 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?

I've no idea. I'm trying to understand what your 'bad case' is 
composed of. You've described the expected case, tested with ftp and 
Samba - but what *exactly* does the bad case consist of?

(We know it involves 'xine' and 'vlc' or somesuch, but you don't seem 
to be inclined to describe exactly how they access the video. By 
reading from NFS or SMB mount? Via HTTP to an Apache server???)

> TBH I don't see how ANY kind of latency issues can explain the 
> client pausing for periods of seconds.

Latency in conjunction with bandwidth determines the required 
buffering.

The size of the buffers involved is determined by the network 
"readers" involved, hence why it why might be an idea to describe 
exactly what your bad case is.

> round-trip min/avg/max = 2.338/24.881/193.09 ms
> round-trip min/avg/max = 2.262/3.67/53.916 ms
>
> So, what the hell is causing that

This kind of stuff seems normal for 802.11. 802.11: the technology 
that brings the feel and experience of yester-year 10Base2/5 networks 
with lots of users on them to you *today* (but without the wires, 
yay).

> - a dodgy AP (mine is a DLink DI-614+) ? 
> And even with those numbers, how are pauses of seconds explained?

They aren't really. Unless your client has a tiny receive buffer. 
24ms / 500kB is well within default sizes on Linux..

> 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 :-)

Nah, 802.11 - it just suck rocks, wirelessly.

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
When you dial a wrong number you never get a busy signal.