I use opus codec for my service. I faced some weird point while running the service.

my setting is ptime 120ms, dtx on,

as I know, if we use dtx feature of opus codec, the maximum period of sid packet is 400ms. but as per my test with ptime 120ms, sid packet's period seems to be increased to 1200ms.

if I set ptime of opus to 20ms, sid packet's period is down to 400ms.

is there any option we need to set to make the sid packet work at 400ms? or is it intended to operate at 1200ms?

does anyone have similar experience?