Hi,
5.4.2020 I bought Dahua IPC HFW5631E-ZE with firmware V2.800.0000010.0.R.190807. After one hour is audio (on YouTube) delayed around 2 seconds. I try different FPS, audio sample frequency, bitrate and another settings in menu. Nothing solved problem. When I switch off NTP, audio delay was 2 seconds from beginning, but constant for all live transmission. I switch off many settings, multicast and other functions.
2.5.2020 I load firmware V2.800.0000005.0.R.190325 (PN). Again 2 seconds constant delay. 4.5.2020 load backup settings from 23.4.2020 and problem solved.
Audio perfect sync with video for all time.
My NTP server is ntp.cesnet.cz (I'am from Czech republic).
I recommend:
1) Flash new firmware
2) Load default factory settings
3) Set NTP server
Thanks for your advices to discover right way. Good luck