[pulseaudio-discuss] 'clicks' in audio and rtp troubles

Lennart Poettering lennart at poettering.net
Mon May 28 10:23:26 PDT 2007

On Mon, 28.05.07 18:56, joysn at gmx.net (joysn at gmx.net) wrote:


> > Are you sure you have set up realtime scheduling correctly? (i.e. have
> > made yourself member of either the group "rt-pulse" or "realtime" --
> > the group name depends on the installation. Debian and PA 0.9.6 and
> > above use "rt-pulse". PA 0.9.5 on non-Debian machines use "realtime".)
> yes. because first i missed to add my account to the pulse-rt and
> pulse-access group. and i'm a member of realtime group to because i use
> jack as my main audio architecture and it needs rt too to work without
> underruns.
> joysn at joysn:~$ pulseaudio -vv --resample-method=src-sinc-best-quality --high-priority=1
> core-util.c: Successfully gained nice level -15.
> core-util.c: Successfully enabled SCHED_FIFO scheduling.
> caps.c: dropping root rights.

Hmm, this probably means you're running a really awful non-"preempt"
kernel whith a large HZ. Last time I looked Ubuntu shipped a shitty
kernel like that. Dunno if they still do. You might want to change

At the cost of higher latency you may fix this by using larger hw
buffers. To do that you have to comment the "load-module
module-hal-detect" line in your configuration and load
"module-alsa-sink" manually. When doing that pass fragment_size=4096
or similar.

See http://pulseaudio.org/wiki/Modules#modulealsasink for more info.

> > > but when i try to access the stream from mac os x and vlc or vlc from
> > > localhost (when configured with loop=1) then i could not connect to it. with 
> > > tcpdump i see lots of packets go to
> > 
> > Last time I looked VLC is unable to pick up SAP announcements from
> > anything but the global SAP mcast group This is a
> > limitation in VLC. Since we don't want to broadcast our RTP sessions
> > all over the Internet we use the link-local group instead
> > by default.
> but its ok to use another mcast group for own streams?

If you limit yourself to link-local mcast groups you can use any you

> > > 13:47:19.281686 IP joysn.local.32809 > UDP, length 1292
> > > 13:47:19.281696 IP joysn.local.32809 > UDP, length 1292
> > > 13:47:19.281703 IP joysn.local.32809 > UDP, length
> > > 1292
> > 
> > Please note that we do not implement RTSP. Only RTP with SAP/SDP. RTSP
> > has been on my TODO list, but I haven't worked on it yet.
> hm. that means that the rtp feature is only working with other
> pulseaudio applications for now?

You can use it with any reasonable RTP app hat can do RTP without
RTSP. mplayer is one of them. pa (of course) is another one. Debian's
"dvbstream" package contains a command line RTP client that should
also be compatible. I heard very recent GStreamer releases learned
RTP as well, so you might be able to construct a pipeline with
gst-launch. Thaytan might know more about this?

Also, a VLC client with minor modifications should be able to pick up
the SAP announcements. (i.e. just replacing the multicasting address
to listen on -- ideally that address should be configurable. maybe it
is time to file a feature request bug for vlc for this)

The only app I tested my code against have been mplayer and
... wireshark. ;-)


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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