[pulseaudio-discuss] Underrunning null sink

[Travis Brown]

After playing around with this for about 6 hours, I found some interesting data.  The latency on the g722 (since renamed to ip_mcast) null-sink hovers around 20mS when I have pavucontrol running, and around 600mS when I don’t have it running.  Since G722 requires pretty consistent 20Ms packets, this is certainly the problem.  The max request size is also obviously different.  Is it possible to adjust the max request size?  That is the only thin gI can think of that would really impact the latency here.

Thanks again,
Travis

Good:
    index: 2
	name: <ip_mcast>
	driver: <module-null-sink.c>
	flags: DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
	state: IDLE
	suspend cause:
	priority: 1000
	volume: mono: 65536 / 100% / 0.00 dB
	        balance 0.00
	base volume: 65536 / 100% / 0.00 dB
	volume steps: 65537
	muted: no
	current latency: 20.63 ms
	max request: 1 KiB
	max rewind: 1 KiB
	monitor source: 3
	sample spec: s16le 1ch 16000Hz
	channel map: mono
	             Mono
	used by: 0
	linked by: 1
	configured latency: 40.00 ms; range is 0.50 .. 2000.00 ms
	module: 4
	properties:
		device.description = "ip_mcast"
		device.class = "abstract"
		device.icon_name = "audio-card”

Bad:
  index: 2
	name: <ip_mcast>
	driver: <module-null-sink.c>
	flags: DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
	state: IDLE
	suspend cause:
	priority: 1000
	volume: mono: 65536 / 100% / 0.00 dB
	        balance 0.00
	base volume: 65536 / 100% / 0.00 dB
	volume steps: 65537
	muted: no
	current latency: 657.77 ms
	max request: 62 KiB
	max rewind: 62 KiB
	monitor source: 3
	sample spec: s16le 1ch 16000Hz
	channel map: mono
	             Mono
	used by: 0
	linked by: 0
	configured latency: 2000.00 ms; range is 0.50 .. 2000.00 ms
	module: 4
	properties:
		device.description = "ip_mcast"
		device.class = "abstract"
		device.icon_name = "audio-card"


> On Oct 24, 2018, at 11:06, Travis Brown <travis at bryx.com> wrote:
> 
> Hi,
> 
>   I am using Pulseaudio to send data from an application to 3 different outputs simultaneously: HDMI, analog output and a G.722 RTP stream.   To accomplish this, I set up a null sink call g722 using the following setting in be default.pa:
> 
>     load-module module-null-sink sink_name=g722 sink_properties=device.description=“g722”
>     load-module module-combine-sink sink_name=combined slaves=alsa_output.pci-0000_00_03.0.hdmi-stereo-extra1,alsa_output.pci-0000_00_1b.0.analog-stereo,g722
> 
>  It actually works pretty great.  I use ffmpeg to pull data from the g722 monitor and transcode it and send it out via multicast to the phones/speakers.  
> 
>     /usr/bin/ffmpeg -re -f pulse -i g722.monitor -filter_complex aresample=16000,asetnsamples=n=160 -vn -ac 1 -acodec g722 -f rtp udp://224.0.2.60:50000 <udp://224.0.2.60:50000>
> 
>  The issue I am having is that ffmpeg underruns most of the time UNTIL I start pavucontrol.  Starting pavucontrol makes things behave beautifully.  ffmpeg gets a constant stream of data and the audio sounds great.  What I cannot figure out is what pavucontrol is doing to make things better.  It must be setting up something for the VU meters, but I am not sure that would actually improve things, or why it would.  
> 
> Thanks,
> Travis
> 

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