G.711 is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at 64 kbit/s. G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second, with the tolerance on that rate of 50 parts per million (ppm). Non-uniform (logarithmic) quantization with 8 bits is used to represent each sample, resulting in a 64 kbit/s bit rate. There are two slightly different versions: U-law is currently being used by companies in North America and in Japan while A-law is being used in Europe. Other areas use a mixture of the two depending on the country.
Oupree Video Encoder supports G711A & G711U and can do resample with 8K for rtsp stream for NVR.
Once your NVR can't get audio correctly, you can set from our video encoder settings.