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Date:      Tue, 7 Aug 2018 02:31:45 +0200
From:      Goran =?utf-8?B?TWVracSH?= <meka@tilda.center>
To:        freebsd-multimedia@freebsd.org
Subject:   Choppy audio using virtual_oss
Message-ID:  <20180807003145.7m55dlakppucpkt2@thinker.home.meka.rs>

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Hello,

To be honest, I'm not sure it's virtual_oss' fault, but here are the
symptoms. When I use mpv to watch video, it glitches and renders really
slowely. When I run jackd and then mpv, everything is fine. Note,
though, that mpv is not compiled with jack support, so this is really
weird. When ardour5 loads a song with "lots" of tracks (around 30-40),
the song plays extremely choppy, although I recorded the whole song last
year using FreeBSD and ardour, so I'm absolutely positive it worked on
the same hardware/software. Here's some relevant info about OS config:

sysctl kern.timecounter.alloweddeviation=0
sysctl hw.usb.uaudio.buffer_ms=2
sysctl dev.pcm.0.play.vchans=0
sysctl dev.pcm.0.rec.vchans=0
sysctl dev.pcm.1.play.vchans=0
sysctl dev.pcm.1.rec.vchans=0
virtual_oss -T /dev/sndstat -S -i 8 -C 18 -c 18 -r 88200 -b 32 -s 384 -f /dev/dsp1 -c 2 -d dsp -c 18 -d vdsp.jack -t vdsp.ctl -M i,0,8,0,0,0 -M i,0,9,0,0,0 -M i,6,8,0,0,0 -M i,6,9,0,0,0
jackd -r -d oss -r 88200 -C /dev/vdsp.jack -P /dev/vdsp.jack -i 18 -o 18

What I didn't try is "sysctl hw.snd.latency=0", which I can try
tomorrow, but I'm not sure it should make any difference.

How can I figure our what's causing this if hw.snd.latency doesn't fix
it? Also, why is "-s 384" recommended? To be more precise, why not 2^n,
but 2^n*3? While I used Linux, I know I read USB audio interfaces should
use "-n 3" for jackd, but I couldn't find the reason why, and I just
guess it has something to do with the value of 384. Of course, I
tried adding that to my jackd command, but it didn't help. I tried
combining "-s 512" for virtual_oss and "-n 3" for jackd, but no luck
either.

If I can provide any other info, please tell me.

Regards,
meka

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