gosrt

This is a SRT library for Go. This is based on the SRT C library.

This library is internally binding SRT C API, but it exposes Go net package like API so that Go programmers can easy to integrate SRT into their application.

Examples

This is a simple example that receive SRT packets from port 5000 and forwards them to localhost port 5001.

l, _ := srt.Listen("srt", ":5000")
defer l.Close()
for {
    conn, _ := l.Accept()
    go func(sc net.Conn) {
        defer sc.Close()
        tc, _ := srt.Dial("srt", "127.0.0.1:5001")
        for {
            b := make([]byte, 1316)
            n, _ := sc.Read(b)
            tc.Write(b[:n])
        }
    }(conn)
}

SRT Socket Options

There are several SRT socket options. You can configure those options with a context.

For example, following code creates a context with options payloadsize to 1316 and latency to 400, then listen and dial with the options.

ctx := srt.WithOptions(context.Background(), srt.Options("payloadsize", "1316", "latency", "400"))

l, err := srt.ListenContext(ctx, "srt", ":5000")

var d srt.Dialer
tc, err := d.DialContext(ctx, "srt", "127.0.0.1:5001")

Following table show how gosrt option corresponds to SRT C API options.

gosrt option	SRT C API option
maxbw	SRTO_MAXBW
pbkeylen	SRTO_PBKEYLEN
passphrase	SRTO_PASSPHRASE
mss	SRTO_MSS
fc	SRTO_FC
sndbuf	SRTO_SNDBUF
rcvbuf	SRTO_RCVBUF
ipttl	SRTO_IPTTL
iptos	SRTO_IPTOS
inputbw	SRTO_INPUTBW
oheadbw	SRTO_OHEADBW
latency	SRTO_LATENCY
tsbpddelay	SRTO_TSBPDDELAY
tlpktdrop	SRTO_TLPKTDROP
snddropdelay	SRTO_SNDDROPDELAY
nakreport	SRTO_NAKREPORT
conntimeo	SRTO_CONNTIMEO
lossmaxttl	SRTO_LOSSMAXTTL
rcvlatency	SRTO_RCVLATENCY
peerlatency	SRTO_PEERLATENCY
minversion	SRTO_MINVERSION
streamid	SRTO_STREAMID
smoother	SRTO_SMOOTHER
messageapi	SRTO_MESSAGEAPI
payloadsize	SRTO_PAYLOADSIZE
transtype	SRTO_TRANSTYPE
kmrefreshrate	SRTO_KMREFRESHRATE
kmpreannounce	SRTO_KMPREANNOUNCE

Run the Example app with Docker

The example app receives SRT packets and sends them to the target address specified in .env file. In the following steps, you can send a test stream from ffmpeg to the gosrt example app, and ffplay play it.

1. Install ffmpeg with srt support

$ brew install ffmpeg --with-srt --with-fontconfig --with-freetype

2. Run ffplay

$ ffplay -probesize 32000 -sync ext 'srt://0.0.0.0:5001?mode=listener'

3. Run gosrt Example app

$ cp .env.sample .env
$ docker-compose up

4. Run ffmpeg

$ ffmpeg -re -f lavfi -i testsrc=size=1280x720:rate=30 -f lavfi -i sine \
-vf drawtext="text='%{localtime\:%X}':fontsize=20:fontcolor=white:x=7:y=7" \
-vcodec libx264 -vb 2000k -preset ultrafast -x264-params keyint=60 \
-acodec aac -f mpegts srt://127.0.0.1:5000