[Solved] how to detect audio playback using only alsa, without pulseaudio

[Rich]

Hi GNUser

... The approach in reply #25 is working reliably and I can understand it, so I'm perfectly happy with it.

That's OK, I was just curious if it worked.

[Rich]

Hi jazzbiker
Straight from:

Code: [Select]

dd --helpIt says (emphasis mine):

  skip=N          skip N ibs-sized blocks at start of input

and:

  bs=BYTES        read and write up to BYTES bytes at a time (default: 512);
                          overrides ibs and obs

[jazzbiker]

Hi, Rich!
Thanks for reminder, i was trying to guess, what is looking suspicious in the command I proposed. Those 1100 are 1K+ header + extra samples, which were to be cut by dd, precise number not significant. I don't believe, that cmp was making mistakes, wrong output meant something was wrong with the input data.

[Rich]

Hi jazzbiker

... I don't believe, that cmp was making mistakes, wrong output meant something was wrong with the input data.

Agreed.

[jazzbiker]

Hi, guys!
Those alsa config, which I've found seems too complicated. Additional module to be loaded, long chain of plugins... Of course it works, but I was anxious about the shorter way. If it is not interesting for You, please don't read this post

So, alsa have the plugin, which can write raw headerless data directly into file. And even more, this data can be redirected to the executable,  .asoundrc attached. As seen, default device data are passed directly to /home/tc/c/vmeter/vmeter binary through the pipe. vmeter source attached. It keeps file /tmp/volume in accordance with the current signal volume of the alsa output. This file can be monitored in any desirable way, for example

w h i l e    t r u e
d o
      r e a d     N < /tmp/volume
      e c h o    $N
      s l e e p   1
d o n e

Must say, that assumptions are made about data format and channels number - signed 16-bit numbers and 2 channels.