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SRT ​

SRT (Secure Reliable Transport) carries live video over the open internet much better than RTMP: it resends lost packets, and it can be encrypted. Use it from remote locations, mobile connections and for contribution between studios.

Enabling it ​

install.sh enables SRT on UDP port 6000 unless you pass --no-srt. In the configuration file:

yaml
srt:
  addr: ":6000"
  latency_ms: 500        # see below
  # passphrase: "..."    # optional: 10-79 characters; then everyone must use it

Open UDP port 6000 in the firewall.

Publishing ​

srt://tv.example.com:6000?streamid=publish:sk_…

In OBS: Service Custom…, that address as the Server, Stream Key empty. With ffmpeg (built with SRT support):

bash
ffmpeg -re -i show.mp4 -c:v libx264 -g 60 -b:v 3M -c:a aac -f mpegts \
       "srt://tv.example.com:6000?streamid=publish:sk_…"

The stream page's Input card shows a Transport stream line: what the encoder sends, checked against TR 101 290 (priorities 1 and 2) while it publishes. Click it for the full report: lost packets, the PCR interval, each PID and the tables the encoder carries. Errors in the last minute raise a warning.

Watching over SRT ​

Unda sends MPEG-TS over SRT (to viewers and to SRT destinations) in messages of whole TS packets, seven at most (1316 bytes), the size hardware decoders and gateways expect.

srt://tv.example.com:6000?streamid=read:main-show

In VLC: vlc --streamid "read:main-show" "srt://tv.example.com:6000". In OBS: a Media Source with Local File unticked and that address as the input. Any live stream can be watched over SRT, however it came in.

Latency and packet loss ​

latency_ms is how long SRT may take to recover lost packets. It must be comfortably more than the round trip between the two ends (check with ping): with 500 ms, a stream with 5% of its packets lost in each direction over an 80 ms round trip arrived complete, while the same link at 60 ms broke. Raise it for long or poor connections; lower it for a local network.

Encryption ​

With passphrase set, every publisher and every SRT viewer must use the same passphrase (OBS: add &passphrase=... to the address; VLC: --passphrase ...). A connection without it is refused.