The local policy for the use of generic RTP Negative Acknowledgements (NACK). Cf. https://tools.ietf.org/html/draft-ietf-rtcweb-rtp-usage-26
NackPolicy is for enabling/configuring negative acknowledgement. Negative acknowledgements are used by media receivers to request that a media sender retransmit a packet. It is highly effective for video in low-latency networks since video is stateful and the cost of losing a packet is high. It is far less effective for audio, where any delay is especially harmful and the cost of losing a packet is not significant. Because of this, it is enabled by default for video and disabled by default for audio. You can modify the buffer size using NackConfig, but generally, it should be left with default values. The option to set these values will most likely be removed in a future release as our adaptive algorithms improve.
public enum NackPolicy : int
The usage of generic NACKs is disabled.
The usage of generic NACKs is negotiated with the peer.