I am currently trying to build a very simple Audio-Tool, which needs to change its name in pavucontrol and qjackctl on runtime. When an Application produces Audio, its name is shown in pavucontrol. E.g. if I use firefox it is shown as "Firefox". I tried the most commonly suggested solutions: Editing argv and using prctl both did not succeed.

I also searched the pipewire documentation but I didn't find anything useful (but maybe I am just blind).

Is it even possible? From where does pipewire get the name of the Application?

Here is a little test-script in C with SDL2:

#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <SDL2/SDL.h>

Uint8* audio_buffer = NULL;
Uint32 audio_length = 0;

void audio_callback(void* userdata, Uint8* stream, int n) {
    memset(stream, 0, n);
}

int main(int argc, char** argv) {

    SDL_Event evt;
    SDL_AudioSpec desired;

    SDL_Init(SDL_INIT_AUDIO|SDL_INIT_EVENTS);

    SDL_LoadWAV("suil.wav", &desired, &audio_buffer, &audio_length);
    desired.callback = audio_callback;

    SDL_OpenAudio(&desired, NULL);
    SDL_PauseAudio(0);


    while (1) {
        while (SDL_PollEvent(&evt)) {
            switch (evt.type) {
                case SDL_QUIT:
                    exit(EXIT_SUCCESS);
            }
        }
    }
}

And a picture of what I would like to have changed on runtime:

(Note: The "test" would be the name in question.)

Disclaimer: I'm not sure if this would maybe sdl-2 specific, so I added the SDL tag.

CodePudding user response：

SDL's Pipewire backend grabs the application name in this block:

/* Get the hints for the application name, stream name and role */
app_name = SDL_GetHint(SDL_HINT_AUDIO_DEVICE_APP_NAME);
if (!app_name || *app_name == '\0') {
    app_name = SDL_GetHint(SDL_HINT_APP_NAME);
    if (!app_name || *app_name == '\0') {
        app_name = "SDL Application";
    }
}

...via the hint system:

• SDL_HINT_APP_NAME:

  /**
   *  \brief Specify an application name.
   * 
   * This hint lets you specify the application name sent to the OS when
   * required. For example, this will often appear in volume control applets for
   * audio streams, and in lists of applications which are inhibiting the
   * screensaver.  You should use a string that describes your program ("My Game
   * 2: The Revenge")
   *
   * Setting this to "" or leaving it unset will have SDL use a reasonable
   * default: probably the application's name or "SDL Application" if SDL
   * doesn't have any better information.
   *
   * Note that, for audio streams, this can be overridden with
   * SDL_HINT_AUDIO_DEVICE_APP_NAME.
   *
   * On targets where this is not supported, this hint does nothing.
   */
  #define SDL_HINT_APP_NAME "SDL_APP_NAME"
  

• SDL_HINT_AUDIO_DEVICE_APP_NAME:

  /**
   *  \brief Specify an application name for an audio device.
   *
   * Some audio backends (such as PulseAudio) allow you to describe your audio
   * stream. Among other things, this description might show up in a system
   * control panel that lets the user adjust the volume on specific audio
   * streams instead of using one giant master volume slider.
   *
   * This hints lets you transmit that information to the OS. The contents of
   * this hint are used while opening an audio device. You should use a string
   * that describes your program ("My Game 2: The Revenge")
   *
   * Setting this to "" or leaving it unset will have SDL use a reasonable
   * default: this will be the name set with SDL_HINT_APP_NAME, if that hint is
   * set. Otherwise, it'll probably the application's name or "SDL Application"
   * if SDL doesn't have any better information.
   *
   * On targets where this is not supported, this hint does nothing.
   */
  #define SDL_HINT_AUDIO_DEVICE_APP_NAME "SDL_AUDIO_DEVICE_APP_NAME"
  

...and then passes the app name into Pipewire using PW_KEY_APP_NAME, here:

PIPEWIRE_pw_properties_set(props, PW_KEY_APP_NAME, app_name);

...where SDL's PIPEWIRE_pw_properties_set() is just a pointer to Pipewire's pw_properties_set().