[pulseaudio-discuss] [RFC] Passthrough support

Arun Raghavan arun.raghavan at collabora.co.uk
Tue Feb 22 09:10:34 PST 2011

On Tue, 2011-02-22 at 10:03 -0600, pl bossart wrote:
> Hi Arun,
> >> > I've updated this page with the changes discussed so far (and translated
> >> > them into the actual API changes that we need). Please take a look and
> >> > let me know if this looks acceptable.
> Couple of comments:
> - There is a miss on the pa_format_info. the sampling frequency is
> required.  The IEC format can be used at various sampling frequencies.
> Passing just IEC isn't enough to configure the link with the receiver.
> The number of channels could be 2 by default, but we may need to
> change this as well for formats like TrueHD or DTS Master.

I figured it'd be best to leave everything but the format in the
proplist and then let the sink pick out the properties it needs/expects.
This allows us to keep the structure generic and lets sinks specify
what/how much information they need to be able to decide whether a
format is supported or not.

> - in case no IEC formats are supported by the sink, what is the
> returned value? If this is NULL, meaning there is no support, how do
> we fall back to plain PCM?

I assume that the every sink that supports PCM will have one format with
PA_ENCODING_PCM in its list of supported formats. With the extended API,
I'd like to treat PCM and compressed formats as being equal as much as

> - in case the routing changes, for example if you plug HDMI or BT, how
> do we change the connection?

The plan is to have clients disconnect and recreate the stream. We could
eventually look at a convenience API to do this.

-- Arun

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