[pulseaudio-discuss] [RFC] Passthrough support

[pl bossart]

>> - I am not sure I understand how/when the query would be used. Seems
>> to me like a notification with the formats exposed by the sink
>> currently selected would be more usable. And if a change in routing
>> happens (new accessory, audio policy, etc), the client is informed and
>> can reconfigure to PCM if need be.
>
> In this scheme, how would the client first determine what formats are
> available? The notification will also be required - we can either
> piggyback in sink, sink-input and card change notifications, or
> introduce a new one for a change in available formats (I prefer the
> latter).

The problem is that you don't know on what sink you will play until
you have actually created the pa_stream. The audio policy and routing
rules may kick in and if you query before you connect you would end-up
with a broken configuration.
One possibly is to connect as PCM, then get a notification from the
sink that it can actually support compressed data and then configure
the stream.
Another possibility is to connect but ask the sink to provide its
capabilities in return. We would then have another call to refine the
stream configuration.
Maybe we should have a short call on this.
-Pierre