Re: Trying to do audio from CGI

On 27/12/20 11:04 am, Alan Corey wrote:
> Uh-oh, I do have PulseAudio installed, didn't intend to.  Using a
> Daniel Thompson Debian Bullseye on a Piinebook Pro.  It's been up less
> than 4 days.  Getting PulseAudio and alsa to coexist is a pain because
> Pulse wants to break alsa.  I did it once following some instructions
> but I have no reason to keep Pulse.  I just tried:

I'm willing to tolerate PulseAudio on my desktop/laptop because it does 
conveniently share the sound card between applications and allows me to 
re-route applications between sound interfaces (something JACK does not 
do well).

I have a Raspberry Pi 3 which spends most of its day with a RTL2832 SDR 
stick plugged in decoding DAB+: I tried PulseAudio there (since it 
insisted on coming along for the ride), but found it just wanted to 
"stutter" its way though, making things unlistenable.

PortAudio applications refused to talk to the on-board sound directly, 
so I wound up using JACK, which is working well enough now.

> cmd: '/usr/bin/mpg123 --output alsa "/data/mp3/pink_floyd/1 - Studio
> Albums/1979 - The Wall/CD 2/Comfortably Numb.mp3" '
> 
> Which I thought I'd tried before, but that was before changing the
> group.  Didn't hear anything but nothing in the Apache error log
> either.  lsof should show the mp3  file open I think.  Or maybe ps ax.
> Could be something in Apache's security but it's calling my CGI
> program OK.  Oh, I'm calling mpg123 from a system() call and not
> checking the return, I was rushing it.

Easy enough to forget that.  Also, beware of command line injection with 
your `system()` calls.  An internal trusted network reduces the risk 
quite a bit, but it's worth being paranoid here.

> The eventual machine will probably be a Raspberry Pi that will get
> used for other things but not at the same time.  I like having it on
> the web (NATed LAN actually) because there are phones, Kindles.
> computers in the house which could all control it.  That part's mostly
> written, trying to actually hear audio was the last part.  I have just
> over 10k MP3 files, but my loader will scan them and make web pages.
> In about 1/2 a second on this nvme SSD so it's painless to generate.
> I'm into writing these recursive directory climbers in c sometimes.

Yep, well, one thing you might run into with a Raspberry Pi… some 
software, notably anything that uses PortAudio (e.g. Audacity), last 
time I tried it a few months back, would _not_ talk to the on-board 
sound interface via ALSA directly.

https://www.raspberrypi.org/forums/viewtopic.php?t=276247#p1750552

I haven't had the time to debug it further, but it's related to changes 
in the ALSA kernel driver used.  Other audio devices like 
`snd-usb-audio` are not affected.

`libao`-based stuff like `mpg123` may be fine.  If you're not doing any 
other "audio"-related things, again, you probably don't need PulseAudio. 
  If you find your program isn't finding the on-board sound card, JACK 
may work, but then again, I've also never tried that in a CGI context.

> Oh, Australia, land of radio astronomy.  I'm ab1jx.  Haven't been on
> the air in 10 years or so but I keep the license up.

Heh, probably not in my neck of the woods (NW Brisbane).  You'd never 
hear E.T. over the top of 10000 el cheapo switch-mode wall warts, solar 
inverters, traffic lights and plasma television sets.  VHF can be noisy 
too being so close to Mt. Coot-tha: I've accidentally tuned into ABC 
Classic FM with a plain analogue amplifier (yaay for accidental slope 
detection!) more times than I care to count,
-- 
Stuart Longland (aka Redhatter, VK4MSL)

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


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