[sndtools] sndpeek on linux, alsa only. info added. partial success

Tristan Matthews le.businessman at gmail.com
Thu Nov 7 13:24:12 EST 2013


On Thu, Nov 7, 2013 at 1:22 PM, Turku Ting <turkuting at gmail.com> wrote:
> ok, i will answer myself one more time hoping someone can help...
> i've managed to set up an alsa Loopback device on my system which works with other apps.
> it's a kind of virtual second soundcard with lots of capture channels.
>
> sndpeek however seems to insist on choosing the first capture device on the first (default) soundcard.
>
> would it be possible to hack the source code so that it goes straight to the second card, hopefully finding the capture audio stream?
>
> i guess some changes would have to be made in RtAudio.cpp...?

Why not use jack?

-t

>
>
> -----------------------------------------------------------
>  basically i want sndpeek to analyze what is playing through alsa.
>  sndpeek _is_ able to listen to my laptops mic if capture is active.
>  i'm too dumb to fully understand the internals of alsa to create a pcm loopback capture.
>
>  short question:
>  can i hack soundpeek to accept raw data?
>
>  long explanation:
>  using mpd (MusicPlayerDaemon), i have various audio output possibilities to provide input forsndpeek, e.g. a fifo that works fine with e.g.
>  $ aplay  -f cd /tmp/mpd.fifo
>  (Playing raw data '/tmp/mpdfifo' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo)
>
>  but
>  $ sndpeek /tmp/mpdfifo
>  returns:
>  [sndpeek]: opening /tmp/mpdfifo...
>  [sndpeek]: error: cannot open '/tmp/mpdfifo':File contains data in an unknown format.
>  [sndpeek]: exiting...
>
>  reading the fifo with sox, transforming it to sth sndpeek understands, and feeding it into another fifo which then can be read by sndpeek kind of works - well, it works but it's really hackish, there's a noticable delay, and sndpeek kind of stutters when i pause/unpause playback. it helps to press f twice (freeze/unfreeze).
>  anyhow, here are the commands:
>  $ sox -t raw -r 44100 -e signed-integer -c 2 -b 16 /tmp/mpdfifo -t wav ~/.config/mpd/wavpipe &
>  $ sndpeek ~/.config/mpd/wavpipe
>
>  so this gives me some info about what kind of input sndpeek needs.
>
>  thanks for reading & maybe some advice.
>
>  tt
>
>
>  > thanks tristan,
>  >
>  > btw i forgot to mention that this is sndpeek compiled for alsa.
>  > i grabbed the git version, now the error reads thus:
>  > [sndpeek]: opening /tmp/mpd.fifo...
>  > [sndpeek]: error: cannot open '/tmp/mpd.fifo':File contains data in an unknown format.
>  > [sndpeek]: exiting...
>  > code 253
>  >
>  > the music player daemon mpd has this in its config:
>  > audio_output {
>  >         type            "fifo"
>  >         name            "My FIFO"
>  >         path            "/tmp/mpd.fifo"
>  >         format          "44100:16:2"
>  > }
>  >
>  > so apart from these 3 numbers i don't really know what format it is.
>  >
>  > what kind of adjustment would the data flowing through the fifo need to be recognizable by sndpeek?
>  > or, what kind of adjustment would sndpeek need to accept/recognize it?
>  >
>  > greetings,
>  >
>  > tt
>  >
>  >
>  > On Mon, 4 Nov 2013 17:48:53 -0500
>  > Tristan Matthews <le.businessman at gmail.com> wrote:
>  >
>  > > On Mon, Nov 4, 2013 at 2:36 AM, Turku Ting <turkuting at gmail.com> wrote:
>  > > > hello,
>  > > > i'd be happy if someone could help setting up sndpeek.
>  > > > i want it to read from a fifo, createt by mpd (music player daemon).
>  > > > i can access the fifo with e.g.
>  > > > $ aplay -f cd /tmp/mpd.fifo
>  > > > but sndpeek just throws a non-descript error:
>  > > > $ sndpeek /tmp/mpd.fifo
>  > > > [sndpeek]: opening /tmp/mpd.fifo...
>  > > > [sndpeek]: error: cannot open '/tmp/mpd.fifo'...
>  > > > [sndpeek]: exiting...
>  > > > code 253
>  > > >
>  > > > any ideas?
>  > >
>  > > You can grab this version of sndpeek, which will at least show you the
>  > > error message from sf_open:
>  > > https://gitorious.org/sndpeek/sndpeek
>  > >
>  > > Best,
>  > > Tristan
>  > >
>  >
>
>
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-- 
Tristan Matthews
web: http://tristanswork.blogspot.com


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