[pulseaudio-discuss] Sink (input) format negotiation concept

[Pierre-Louis Bossart]

On 8/18/16 11:43 AM, Rémi Denis-Courmont wrote:
> 	Hello,
>
> For a number of years already, PulseAudio has supported a concept of sink
> inputs with multiple formats. That is meant to support S/PDIF output in
> addition to PCM.
>
> One thing I´m wondering... what is the expected behaviour for an application
> to negotiate non-PCM format for a stream? Specifically, if the application
> supports IEC 61937, should it always offer the relevant format (in addition to
> PCM fallback) when creating the stream? Or should it do so only if the user
> has somehow enabled that feature?
>
> In other words, is PulseAudio supposed to know if IEC 61937 will actually
> work, or is it merely naively listing the formats that the sound card allows,
> without regards to adequate speaker presence?

The sound card itself only pushes the compressed format on HDMI or 
SPDIF, it doesn't really know what formats are embedded in the payload. 
To know what the receiver supports once can read the EDID/ELD 
information, but this is only for HDMI/DP and not for SPDIF, and it's 
often corrupted/invalid. If I remember well the solution is to let the 
user specify what formats work rather than guessing or relying on 
invalid data.
Arun may have a better memory than me on this.