sound redirect does not work on gentoo

[guyuming76]

i can connect to xrdp running on gentoo through xfreerdp: neutrinolabs/xrdp#1796

but the sound redirection does not work even though i added /sound:latency:100 parameter in xfreerdp command.

xrdp works with sound redirection on my ubuntu machine, where i need to use pulseaudio -k to restart the pulseaudio service after sign in through xfreerdp. i use "pactl list modules short" to show pulse modules loaded in xrdp session. i can see that before pulseaudio -k, the module-xrdp-sink is not loaded, and it is loaded after pulseaudio -k.

but on my gentoo system, module-xrdp-sink never load.

i use OpenRC instead of systemd on gentoo, and start xrdp by running xrdp-sesman and xrdp with root in console.

i can see module-xrdp-sink.so in results of "ls $(pkg-config --variable=modlibexecdir libpulse)"

what can be wrong and what shall i check?

UPDATE: i can see "module-xrdp-sink.c: Invalid sample format specification or channel map" error