[pulseaudio-discuss] Multiple RTP Receivers not in sync

Sebastian Stuecker sebastian.stuecker at googlemail.com
Sun Apr 15 03:01:19 PDT 2012


I am building a whole home audio solution with a central server that has
several mpd instances connected each to a pulseaudo null sink and all those
null sinks have their corrosponding RTP sender and use different multicast
IP adresses (parameter "sap_address").

I have then multiple receiving units throughout my house and with them i
"tune" to the different rtp streams coming from the sender. Of course I
want to tune more than one receiver to the same RTP stream so I listen to
the same music in multiple rooms. Since those rooms are adjacent to each
other it is vital that the audio is in sync, otherwise I have echoes or
even larger lags which is very annoying.

As far as I understood the pulseaudio rtp implementation, those receivers
SHOULD be automatically in sync. I have an ntp daemon running on all
receivers and their sync to an ntp daemon running on the server. I have
manually checked clock sync and as far as NTP precision goes, the clocks of
all hosts (both sender and receivers) are in perfect sync.

BUT, the sound is not. I have lags of up to 1-2 seconds. Everytime i
restart the pulseaudio daemon on a receiver the sync lag is different.
Sometimes it is in very good sync but then it looses sync over time.

Is there any way of debugging/tuning this? The logoutputs of the sender and
receivers look "normal" so they tell about rate adjustments all the time
but I understand this is the way how it just works.

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