WebRTC: Support GCC and FEC for weak network.

[flying1314]

Description
Currently, WebRTC does not have a related QoS (Quality of Service) policy. If streaming is done in a weak network environment, the quality might be relatively poor, without congestion control and pacing sender.

Expected Behavior
It would be great to add QoS support.

[winlinvip]

What is the current proportion of weak networks? How much weak network resistance can the NACK and ARQ already supported by SRS provide?

[flying1314]

Using clumsy to simulate packet loss, it doesn't work well with 10% packet loss.

[dongzy08]

Is there any consideration for supporting FEC (Forward Error Correction) strategy in the future?

[streamthing]

+1 for fec

[HammerZhao]

NACK should have no problem combating 20% packet loss, right?