Hello.
I needed a tool to test if anything loud is playing right now. So I wrote "ahwmon" - alsa hw monitoring tool. It's based on dmix idea: it gets "hw" shared playback buffer, but reads from the buffer instead of writing.
Code is mostly copied from alsa-lib, but it uses kernel /dev/snd/pcm* files directly and doesn't depend on alsa-lib or dmix. May work for other apps playing to "hw", including pulseaudio and jackd.
What do you think about it? Can something like this get into alsa-lib or alsa-utils or alsa-plugins? It could be a capture side of "dmix" plugin, which has no capture now. Maybe someone with strong dmix knowledge can port it to dmix?
Build: gcc -o ahwmon ahwmon.c
Usage: ./ahwmon [-v] [-v] <card_index> <device_index> [<subdevice_index>] subdevice 0 is used by default it outputs .wav stream to stdout
Use cases: * Card VUmeter: ./ahwmon 0 0 | aplay -V stereo -D null * Dump what you hear: ./ahwmon 0 0 > audiodump.wav * Duplicate output of one card to another: ./ahwmon 0 0 | aplay -D plughw:1,0 * Stream what you hear to another pc: ./ahwmon 0 0 | nc 192.168.1.10 12345
Known limitations: * supports S16_LE and S32_LE only. * breaks clients attempting to close and reopen "hw"
Any ideas are welcome!