Transcoding on Playback function

Hi,

I configured a sip phone with g722 (or speex16) and I don’t understand why I cannot only put a .slin16 file on /var/lib/asterisk/sounds/en folder to play file with Playback function. the system should transcode it from slin16 to g722 (or speex16).

Note: if I add a g722 file on /var/lib/asterisk/sounds/en, I have no issue.

Asterisk 18.1.1

Thanks
Anthony