[streaming] Re: Packet loss in streaming with my IP box using vlc

[Jean-Paul Saman]

deepak SoundaraRajan wrote:

>  Hi 
>	We have designed a IP steraming box using PowerPC processor of 350 MIPS speed along with 64 MB ram & 10 mbps ethernet.
>I ported vlc 0.7.0 to that box and tried UDP/RTP streaming.
>  
>
I think you can better use a more recent version of VLC. Version 0.7.0 
is known to leak memory, so it won't be stable overtime. Version v0.7.2 
should be more stable for your product.

>I use vlc for windows as my streaming server in xeon processor.
>
>Observations
>------------
>1)when we transmitt with a MPEG2 stream in 512kbps bitrate from server and try to stream with IP box there is negligible packet loss
>and no flickering in video.
>2)when we try with 1 mbps & 1.5 mbps bitrate there is some packet less & very less flickering.
>3)when i with more than 1.5 mbps there is heavy packet loss & more flickering in video.
>4)when we try in Linux PC as streaming client in same network it works fine,but our box gives above problem.
>5)Even we tried directly connecting the IPbox to the server using cross cable,the problem persists.
>
>  
>
If I understand correctly streaming from a PC to a PC over the same 
network doesn't give problems with regard to packet loss and video size. 
Streaming to your IP setopbox does.

Does both PC have a 10 Mbps network connection?
What is the available memory left for VLC on the IP box?
What is the CPU utilization of the IP box before VLC runs? And when VLC 
runs ?

All above suggest that your IP box has trouble keeping up with the 
incoming network stream.
1) I would analyze first if there is enough time left to read the 
network socket without dropping packets. Use a tool like iperf. It will 
tell you where the limits for your IP box are with respect to network 
traffic.
2) Once verified that this is not a problem, then look into VLC's 
memory/cpu consumption and how much is left on the IP box.

>My doubts
>---------
>1)Does vlc requires more memory & processing power for handling higher bitrate streams.
>  
>
Higher bitrates, larger videoscreen directly results in more need of 
memory on the client side. In principle you can say the amount of memory 
needed for a stream on a PC is the amount the client will need when 
streaming/playing when that is a setopbox.

>2)whether 10 mbps ethernet is not sufficient to stream more than 2 mbps bitrate stream.
>  
>
If the network link is more saturated then 70 % problems can be 
expected, but below that figure all will be fine.

>3)buffering is not for vlc for reading the ethernet socket.(As i saw in vlc/modules/misc/network/ipv4.c that 0.5 mb buffer is needed to avoid packet loss but linux allocates less than that)
>  
>
Try enlarging these will help:

sysctl -w net.core.rmem_max=131070
sysctl -w net.core.rmem_default=131070

sysctl -w net.core.hot_list_length=512
sysctl -w net.core.netdev_max_backlog=1300

You will have to experiment with the figures. The above is roughly twice 
the defaults from the kernel.

-- 

Many greetings,
Jean-Paul Saman

Consultant
--------------------------------------------------------------
VLC iPAQ maintainer                    http://www.videolan.org
RedHat Certified Engineer         RHCE number: 807202745005548
--------------------------------------------------------------

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