[Icecast] ices-kh60: latency bug

Andy Baxter andy at earthsong.free-online.co.uk
Sun Dec 18 17:55:42 PST 2005


On Sunday 18 Dec 2005 20:27, Karl Heyes wrote:
> Andy Baxter wrote:
> > hello,
> >
> > I've just got ices-kh60 running with jack. It's working OK apart from a
> > problem where the latency on the stream creeps up from about 15-20 secs
> > to around 7 minutes. The stream plays OK, but the audio coming out is 7
> > minutes behind what goes in. I'm not sure how this can be happening,
> > seeing as I don't think there are any buffers that long in the system,
> > but it is. I've checked that it's not a problem with the player app I'm
> > using (amarok), and it isn't - even if I reconnect the stream, there is
> > still a long latency.
> >
> > I suspect the problem is caused by running the stream for long periods
> > with no audio input (zero sound level from an unconnected jack graph), as
> > this is what seems to cause it.
>
> There are two places that spring to mind.
>
> Icecast 2.2 did have a problem in certain cases when it came across
> digital silence. The problem manifested itself by increasing the burst
> at start-up (increasing latency), 2.3 did correct for this so doesn't
> suffer from it.
>
> The data delivered to ices is regulated by jackd and it has been known
> that the jackd dummy driver has had next to useless timing, make sure
> you use the alsa driver in jackd.
>
> karl.

I just tried using icecast v2.3, and it's still an issue - at first it's 
slightly better with the latency starting off at around 10 seconds, but then 
it creeps up to several minutes as before (when the jack input is 
disconnected). This is with a jack graph that looks like this:

ecasound -> ices

and nothing feeding into ecasound.
(ecasound is there to provide a compressor plugin for the sound level)

I don't know what jack does with an empty input - whether it feeds it digital 
silence, or simply stops processing that part of the graph. In any case it's 
still happening. Jack is using the alsa plugin.


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