[vls-devel] Re: Occasional crazy problem with vls

[Jean-Paul Saman]

Andrew de Quincey wrote:
>>>>Note that the problems doesn't always occur... usually videolan behaves
>>>>correctly with high loads, but as I said, occasionally this problem
>>>>occurs. I'm guessing this is some timestamping problem caused by the
>>>>high load, as the file plays perfectly in videolan at all other times.

It also depends on when the bitrate peaks in the streams align. A normal 
DVB based MPEG2 has a bitrate of 4-5 Mbps on average but they can peak 
uptill about 8 Mbps.
Now when ALL your streams on a loaded disk (high-load), about 11-12 
streams have the peak at the same time, then VLS HD requests are not 
served in time. The result ... well you've seen ;-)
How much streams need to be peaking at the same time depend on the PCI 
bus and HD capabilities, but you can calculate the worst case for that. 
Normally there is about 50 MB bandwidth to the disk in a computer system.

>>>>I'm asking this because (for various reasons) I'm not using the most
>>>>recent version of videolan, although I'm not that far behind. Has
>>>>anyone fixed anything like this recently (before I start looking)?

>>>I don't think it is a problem as such of VideoLAN. What happens in this
>>>scenario is that the copy of the new mpeg file is messing up the
>>>harddisk cache. In fact all VLS request for data from the same disk
>>>start starving and this will result in sending out *late* packets like a
>>>mad man ;-).
> 
> 
> I'm not sure if the IO explanation is quite the reason... see that was just 
> how I managed to duplicate it. This occurs at random on video servers which 
> we know are not having large files or any load of that sort occurring to 
> them. The only load is from streaming video either from disk, or from 
> DVB-T/DVB-S cards directly to the network interface.
> 

The two years our VLS server is streaming to multiple clients while 
recording another stream I never saw this behaviour. Unless the disk was 
overloaded.

But did your clients expirience a still frame or black frame for some 
time when copying the large file ? you haven't answered this question.

-- 
Kind greetings,

Jean-Paul Saman



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