[core] Added SRTO_MININPUTBW

[maxsharabayko]

A simplification of #1541 and #1383.
The proposed SRTO_MININPUTBW socket option allows specifying the minimum input bitrate estimate used to set bandwidth limit.

Effective when SRTO_INPUTBW = 0 -> input bitrate estimation.

input_rate = max(SRTO_MININPUTBW, estimate)
BWLimit = input_rate * (1 + SRTO_OHEADBW / 100.0)

TODO

• Update APISocketOptions.md

[jeandube]

Way simpler than the SRTO_OUTPACEMODE option it replaces. Maintain backward compatibility but setting both SRTO_INPUTBW and SRTO_MININPUTBW would lead to unexpected results. The documentation should clarify that SRTO_MININPUTBW is a floor to the internally measured input rate.

[maxsharabayko]

Way simpler than the SRTO_OUTPACEMODE option it replaces. Maintain backward compatibility but setting both SRTO_INPUTBW and SRTO_MININPUTBW would lead to unexpected results. The documentation should clarify that SRTO_MININPUTBW is a floor to the internally measured input rate.

The proposed behavior is that SRTO_MININPUTBW is only effective when both SRTO_MAXBW and SRTO_INPUTBW are set to zero, meaning input bitrate estimation is in use.

[maxsharabayko]

Test

Sending starts at 1 Mbps, five seconds later sending rate is increased to 5 Mbps.

Input BW Estimation

SRTO_MAXBW = 0
SRTO_INPUTBW = 0; // Estimate internally
SRTO_OHEADBW = 25;
SRTO_MININPUTBW = 0;

Input BW Estimation + Setting Min Input BW

SRTO_MAXBW = 0
SRTO_INPUTBW = 0; // Estimate internally
SRTO_OHEADBW = 25;
SRTO_MININPUTBW = 1 Mbps;
// Once "encoder" changes sending rate from 1Mbps to 5Mbps
SRTO_MININPUTBW = 5 Mbps;