RTX codec parameters, i.e. RTX-time

[robin-raymond]

If a receiver is configured to "latch all", i.e. no encoding parameters listed and an RTX codec is listed, how does the receiver know the RTX-time since that is only specified currently within the encoding parameters?

[aboba]

Should we add rtxTime as a parameter of the RTX codec?

[robin-raymond]

for RTX codec, we need optional param ulong CodecParameters.parameters.rtxTime

From RTC:

      indicates the time in milliseconds (measured from the
      time a packet was first sent) that the sender keeps an RTP packet
      in its buffers available for retransmission.

Also, inside EncodingParameters.rtx we need a mandatory EncodingParameters.rtx.codecPayloadType which points to the codec from the CodecParameters list to use for RTX when RTX is enabled. NOTE: Alternatively, it can be made optional and the engine can 'guess' the codecPayloadType based upon only one match existing with the same Hz rate as the main codec. If multiple matches exist though it would be an exception.

EncodingParameters.rtx.rtxTime is not required because the rtxTime should be taken from the CodecParameters.parameters.rtxTime where the rtx.codecPayloadType points.