**SRT: Support PUSH SRT by IP and optional port.** Support streaming by IP and optional port.

[winlinvip]

Some device only support IP and an optional port, for example:

srt://192.168.1.100:10080

Where SRS's server IP is 192.168.1.100 which can be a public internet IP.

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[xiaozhihong]

By quink:

FFmpeg/FFplay has several usage modes: 

---------------------------------------------------------------------------
Simulate server to test streaming playback:

Listener passively pushes the stream (write):
./ffmpeg -re -i  ~/video/cctv.mp4 -c copy -f mpegts -mode listener srt://127.0.0.1:6666

Caller actively pulls the stream (read):
./ffplay srt://127.0.0.1:6666

----------------------------------------------
Simulate server testing for streaming.

The listener passively receives (reads).
./ffplay -mode listener  srt://127.0.0.1:6666

The caller actively pushes the stream (writes).
 ./ffmpeg -re -i  ~/video/cctv.mp4 -c copy -f mpegts srt://127.0.0.1:6666

----------------------------------------------
./ffmpeg -h protocol=srt
-mode              <int>        ED......... Connection mode (caller, listener, rendezvous) (from 0 to 2) (default caller)
     caller          0            ED.........
     listener        1            ED.........
     rendezvous      2            ED.........

The caller is the default and all three types are supported.

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The above is not feasible for SRS because SRS is a server and needs to know whether the client needs to pull or push the stream. The so-called Caller and Listener mode is just a logical distinction and cannot be used to obtain the peer's mode after the communication is established, similar to using interfaces like srt_getsockopt(SRTO_MODE) (there is no such SRT socket option). Therefore, in the absence of a stream ID, the server can only assume that the other party is pushing the stream.

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