[pulseaudio-discuss] how to pass correct channel map

[Sean Greenslade]

>On Wed, Sep 15, 2021 at 10:36:23PM -0700, Sean Greenslade wrote:
>> On Wed, Sep 15, 2021 at 09:59:00PM +0530, Vijendar Reddy Mukunda wrote:
>> > Hello,
>> > 
>> > I was just experimenting with a null sink.
>> > I have created null sink with 48000Hz sample rate, s16le, channels as 6.
>> > Tried to record from null sink monitor source.
>> > But when i run parecord command, I am seeing the below error.
>> > Warning: failed to write channel map to file.
>> > I have also tried null sink creation
>> > with channel_map=front-left,front-right,rear-left,rear-right,front-center,lfe.
>> > But no luck.
>> > Need inputs on fixing this channel map issue.
>> 
>> That error is just a warning, and can most likely be ignored. Not all
>> sound formats actually support writing the channel map into them. In
>> fact, according to the libsndfile docs, only AIFF and CAF are supported:
>> 
>> https://libsndfile.github.io/libsndfile/command.html#sfc_set_channel_map_info
>> 
>> What file format are you using?
>
> Thank you for your explanation.
> We are trying to play youtube content.
> One more question on the same line.
> we have created a null sink with 192khz/8ch/s32le and channel map as
> "front-left,front-right,rear-left,rear-right,front-center,lfe,side-left,side-right"
> When we record null sink monitor output, we are seeing complete silence
> in one channel.
> As we are using lfe as one channel, do we need to do any extra settings
> on lfe channel?

Well, does your source media have 7.1 channel audio? If not, you'll need
to turn on the "remixing-produce-lfe" setting in daemon.conf. If it
does, then you'll need to dig deeper into what exactly your playback
software is doing.

--Sean