[pulseaudio-discuss] PA_CORE_HOOK_SINK_INPUT_PUT

[Nick Thompson]

Hi,

I posted yesterday, and whilst I didn't figure out an answer the  
question about the sequencing of the _put call, I did find another way  
to get what I need.  I wanted to get the index of a sink input after  
creation, but before it plays, so that I can implement sink-input  
switching and other stream manipulation (volume changes, etc.) in  
response to audio policy changes, on an embedded system.

I can't explain why _put is called after the stream completes  
playback, but I did discover a different way to be notified of sink- 
input creation with the completely filled sink input, using  
pa_subscription.  Recall that neither sink-input new hook or the sink- 
input fixate hook will call back with a complete sink-input (the index  
of the sink-input has not been set with either) and that I was not  
seeing the sink-input put hook being called until after a stream had  
completed playback.  So the method I came across (modified from one of  
the existing module sources) is as follows.

Install a subscription routine using in the module init routine:

     u->subscription = pa_subscription_new(m->core,  
PA_SUBSCRIPTION_MASK_SINK_INPUT, subscribe_callback, u);

This allows us to get notifications on sink-input creations.  When  
this routine is called back, it will be passed the index of the  
created sink input which makes getting at the actual sink-input to  
inspect it's fields really easy.

Here is a subscribe callback to do this:


static void subscribe_callback(pa_core *c,  
pa_subscription_event_type_t t, uint32_t idx, void *userdata) {
     struct userdata *u =  userdata;
     pa_sink_input *si = NULL;

     pa_assert(c);
     pa_assert(u);

     pa_log("> pa__init");

     /* we are only interested in sink-input creation events */
     if (t != PA_SUBSCRIPTION_EVENT_SINK_INPUT| 
PA_SUBSCRIPTION_EVENT_NEW) {
         pa_log("< pa__init - not a new sink input");
         return;
     } else {
         if (!(si = pa_idxset_get_by_index(c->sink_inputs, idx))) {
             pa_log("< pa__init - can't get index");
             return;
         }
     }

     pa_log("new event received on sink-input with index %d",si->index);

}

Regards

Nick

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