Re: Trying to do audio from CGI

On 27/12/20 7:33 am, Alan Corey wrote:
> Directory:/data/mp3/Queen/-- Studio Albums --/(1975) A Night at the Opera/
> Playing MPEG stream 1 of 1: 11 Queen - Bohemian Rhapsody.mp3 ...
> [src/libout123/modules/portaudio.c:120] error: Failed to open
> PortAudio default stream: Device unavailable
> main: [src/mpg123.c:323] error: out123 error 7: failed to open device
> 
> Why is it now trying PortAudio?  And failing - Audacity works with it.
> Could it be something not in www-data's path?

It might be a default for `mpg123` or `libao` (the back-end library used 
by `mpg123`).  I haven't used `mpg123` for a long time now but I think 
in the man page, there's a documented flag to point it at a different 
back-end such as ALSA directly.  (I switched to Ogg/Vorbis to "clean" 
out the illegally downloaded files I had in that format, and because 
MP3's licensing was a pain back in 2004.  As a bonus, storage 
requirements shrunk by 40%.)

If the machine is acting as a music jukebox and nothing else, it 
probably makes sense to disable PulseAudio in this situation since 
there's only the one "user" of the sound card, PulseAudio really doesn't 
offer much other than maybe Bluetooth speaker connectivity (and there 
are ways to do that without PulseAudio too).

PulseAudio will need the user that runs it, to have "real-time" rights 
(configured in `/etc/security/limits.conf`).  Not sure if `www-data` 
will have those rights as it's a rare requirement for CGI scripts. 
Alternatively, I think PulseAudio can be run in a "system" mode, have a 
read of its documentation, maybe that might work in your situation.

The other option you might want to look into, rather than trying to make 
PulseAudio or ALSA work as the CGI user, instead look at making a 
back-end daemon look after whistling up `mpg123` to play music, and have 
the CGI script talk to it via some IPC mechanism (SysV IPC, Unix domain 
sockets, private HTTP API, Redis/AMQP/MQTT whatever).

I'd strongly suggest having a look at `mpd`, as while there's probably 
some educational value to re-inventing the wheel, it looks like 
someone's done the work for you: `mpd` itself can act as that back-end 
service, and there are already web-based front-ends to talk to it.
-- 
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
   ...it's backed up on a tape somewhere.