Hm. It's not so much about allowing it, but about making it possible.
We read the keys for terminal control from stdin. If that's stuffed
with MPEG data, there might be the way to access /dev/pts/n instead, or
whatever stderr is still linked to. At least the tty command uses that
approach to figure out the controlling terminal. But that is not
terribly portable.

I tried a bit of hacking with hardcoding my current pty and so far
notice that select() on that doesn't work. We need that for interactive
use.

I might have gotten something wrong. But when we are limiting things to
certain platforms already … what about doing what in bash would be

mpg123 -Cv <(some_program)

? You can pass a file descriptor down to mpg123, not clogging stdin.

so the script is not in bash but in sh
how do you see the following rewritten to allow control ?

play() { # receive /track/1,2,3 from stdin
        xargs basename | xargs $0-url | while read url id; do
#               $FETCH "$url" | $0-dec $id | eval ${PLAYER:-'mpv -'} ; #mpv works just fine with stdin and cli commands
               $FETCH "$url" | $0-dec $id | eval ${PLAYER:-'mpg123 -vqC -'} ;
        done
}

reference: https://github.com/yne/dzr/blob/3634e091417d94a89f3e56b0226a7215b0c79798/dzr#L33

thanks,
M

I've tried to build and install (make) the snapshot code but it doesn't work:
main: [src/mpg123.c:check_fatal_output():331] error: out123 error 3: failure loading driver module
and about mpv as I'm not that advanced into C coding I can just reference what I think it's the control functions https://github.com/mpv-player/mpv/blob/master/input/input.c

Regarding the failure: You need to run src/mpg123-with-modules or simply give --disable-shared to configure to avoid the run-time linking issues.

Edit: Or just do a make install and run from the installed prefix.

I did the following:

./configure --disable-shared
make
sudo make install

and indeed running the binary outputs the help (no more complains about missing binaries - previously fixed with export LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib - FIXED the command with export - wrong copy/paste :) )
but running it in the dzr script (mpg123 -qvC -) outputs the same error:
main: [src/mpg123.c:check_fatal_output():331] error: out123 error 3: failure loading driver module

That doesn't make sense … or … hm … well, yes, you need to select the proper output module with --disable-shared. The one that works at runtime. If you install into a prefix and have that in PATH for dzr, then just keep the default config, just add --prefix. Then it should behave the same as your distro package — provided you got the development files installed for the output API you use!

I fixed up the current snapshot to simply use /dev/tty or ctermid() for control keys. Simple. Can you test that (and figure out your installation issue)?

thank you for the quick answer.
I'll need some help though to make get this dev version working in my env - ubuntu 20.04 as even if I try to add in the dzr script with the full path like /home/user/mpg123-20220507022201/src/mpg123 -vqC - I still get the error :( main: [src/mpg123.c:check_fatal_output():333] error: out123 error 3: failure loading driver module
in the bash console it works without issues

I suspect that you do not have the correct output module built for your setup (missing development package). Can you show the output of mpg123 -vvv -n 1 testfile.mp3 for both your system-installed mpg123 and the self-built one?

Trying output module: alsa, device: <nil>
Using default module dir: /usr/lib/x86_64-linux-gnu/mpg123
Module dir: /usr/lib/x86_64-linux-gnu/mpg123
Module path: /usr/lib/x86_64-linux-gnu/mpg123/output_alsa.so
Chosen output module: alsa
…
Audio driver: alsa
Audio device: (null)
Audio capabilities:
(matrix of [S]tereo or [M]ono support for sample format and rate in Hz)

I am looking for such lines … also, the output of mpg123 --list-modules confirms the list of available outputs and a likely difference between your system one and the self-built one. Maybe you are missing pulse headers and only have OSS support built? When you use --disable-shared, you need to specify the output module you want to build in using --with-audio=pulse for example/.

it looks like you're right - my compilation is botched :)

$ mpg123 -vvv -n 1 ./Downloads/file_example_MP3_700KB.mp3
High Performance MPEG 1.0/2.0/2.5 Audio Player for Layers 1, 2 and 3
    version 20220507022201; written and copyright by Michael Hipp and others
    free software (LGPL) without any warranty but with best wishes
Decoder: x86-64 (SSE)
Trying output module: oss, device: <nil>
Note: oss is the last output option... showing you any error messages now.
[src/libout123/modules/oss.c:open_oss():174] error: Can't open default sound device!
[src/libout123/libout123.c:check_output_module():982] error: Module 'oss' device open failed.
[src/libout123/libout123.c:out123_open():482] error: Found no driver out of [oss] working with device <default>.
main: [src/mpg123.c:check_fatal_output():333] error: out123 error 3: failure loading driver module

So you maybe just need to install something like libasound2-dev or libpulse-dev before compiling, depending on what sound system you use.

If run a normal desktop with pulseaudio, using that directly is better than via alsa/asound, but both should work. Just check which backend is used with your system install of mpg123.

got it finally:

sudo apt install libpulse-dev
./configure --with-audio=pulse --disable-shared

I can confirm that control works now via stdin - awesome job !!!
Looking forward to the next stable release !

PS - Any pointer to how to statically cross compile this for a low end system like raspberry pi ? - aka i just want to transfer 2-3 compiled files maximum to /usr/bin and use it ?

and a very big thank you for all your development and community support !

Cool. For a cross-build, you should be on the right track. Without shared stuff, mpg123 just links to libc and your audio backend. If the raspi also has libpulse, you only need the cross-dev files for that. Nothing special about mpg123 … it's GNU autoconf with standard support for cross builds. So having a toolchain and using the appropriate standard options should get you far.

thank you very much again !