[pulseaudio-discuss] [RFC] Passthrough support

Tanu Kaskinen tanuk at iki.fi
Mon Feb 28 22:28:35 PST 2011

On Mon, 2011-02-28 at 16:48 -0800, Christ Schlacta wrote:
> On 2/27/2011 23:29, Arun Raghavan wrote:
> > On Sun, 2011-02-27 at 23:20 -0800, Christ Schlacta wrote:
> > [...]
> >> mark settings as optional or required for negotiation.  if one or the
> >> other can't support an "Optional" parameter, then it gets replied to as
> >> unsupported but continuing.  a warning is logged.  a mandatory option
> >> will cause it to fail with an error message logged (Warning, Remote sink
> >> doesn't support required option "bitrate".  either upgrade Remote Sink,
> >> or set bitrate as optional by using "optional bitrate foo") or similar.
> > We can do this, but what does it really get us? On the sink side, we
> > know what restrictions we want to place on the input, and it's
> > reasonable to assume anything unspecified is fine (if it's not, it
> > should be specified as a restriction anyway).
> >
> > On the stream side, we're not providing the information as a restriction
> > - we're saying "I have this stream, it can be with one of these
> > formats/properties, find me a sink to plug into". What would an optional
> > parameter achieve here?
> >
> the optional parameter says "If you don't have this, it's fine", whereas 
> the mandatory parameter says "If you don't have this, then fail".  It 
> allows older and newer software to interoperate, if one end of the 
> connection doesn't know about a parameter, it only matters if it's 
> mandatory.  the point of the thread was how to allow future changes of 
> parameters without breaking compatibility..  that would achieve that 
> goal, while allowing the two ends to negotiate when to succeed and when 
> to fail, vs. just always trying or always failing.

Yes. Just to clarify your point - by an "optional" parameter you
probably mean that for example a sink can declare that it supports any
sampling rate. That can be represented for example by making "any" a
special value in the format info property list.

I thought first that you meant that every property should be marked
explicitly as mandatory or optional, and sinks could say that "I support
only 48000 Hz sampling rate, but by the way, that's optional, so ignore
that", which wouldn't make any sense. So, I thought a clarification was


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