I'm no expert but I'm pretty sure I had to add the output_args record: preset-record-generic-audio-aac to get audio on one of my cameras. Maybe give that a try?
##### Cams #####
cameras:
front_door:
ffmpeg:
inputs:
- path: rtsp://redacted/h264/ch01/main/av_stream
#input_args: preset-rtsp-restream
roles:
- record
- detect
output_args:
record: preset-record-generic-audio-aac
objects:
track:
- person
Worth a shot I guess. I also confirmed I'm using a go2rtc stream in my home assistant card with MSE as the go2rtc mode. Not sure if this is going to work but I'm attempting to attach a screenshot of my card settings in case there is anything there that may help
(edit) - Can't quite figure out how to get a pic to display...