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srt: Nginx SRT Module

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

  • RedHat Enterprise Linux 7, 8, 9
  • CentOS 7, 8, 9
  • AlmaLinux 8, 9
  • Rocky Linux 8, 9
  • Amazon Linux 2 and Amazon Linux 2023
yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install nginx-module-srt

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_srt_module.so;

This document describes nginx-module-srt v1.1 released on Feb 05 2024.


Haivision SRT (Secure Reliable Transfer) / TCP gateway. Supports both SRT to TCP and TCP to SRT, including bidirectional data transfer.

The implementation uses libsrt for SRT communication. The libsrt code executes on a side thread, eventfd notifications are used in order to communicate with the main nginx thread.

Configuration

Sample configuration

## SRT -> TCP proxy
srt {
    server {
        listen 4321;
        proxy_pass tcp://127.0.0.1:5678;
    }
}

## TCP -> SRT proxy
stream {
    server {
        listen 5432;
        srt_proxy_pass srt://127.0.0.1:4321;
    }
}

srt core directives

srt

  • syntax: srt { ... }
  • default: -
  • context: main

Provides the configuration file context in which the srt server directives are specified.

server

  • syntax: server { ... }
  • default: -
  • context: srt

Sets the configuration for a server.

listen

  • syntax: listen address:port [backlog=number] [bind] [ipv6only=on|off] [reuseport];
  • default: -
  • context: server

Sets the address and port for the UDP socket on which the server will accept connections.

See the documentation of the listen directive of the nginx stream module for more details on the optional parameters supported by this directive.

variables_hash_max_size

  • syntax: variables_hash_max_size size;
  • default: 1024
  • context: srt

Sets the maximum size of the variables hash table.

variables_hash_bucket_size

  • syntax: variables_hash_bucket_size size;
  • default: 64
  • context: srt

Sets the bucket size for the variables hash table.

error_log

  • syntax: error_log file [level];
  • default: logs/error.log error
  • context: srt, server

Configures logging, see the documentation of the nginx core error_log directive for more details.

fc_pkts

  • syntax: fc_pkts number;
  • default: 25600
  • context: srt, server

Sets the maximum number of "in flight" packets (packets that were sent, but not yet acknowledged).

See the libsrt documentation of the SRTO_FC option for more details.

mss

  • syntax: mss size;
  • default: 1500
  • context: srt, server

Maximum segment size, in bytes.

See the libsrt documentation of the SRTO_MSS option for more details.

recv_buf

  • syntax: recv_buf size;
  • default: 8192 buffers
  • context: srt, server

Receive buffer size, in bytes.

See the libsrt documentation of the SRTO_RCVBUF option for more details.

recv_udp_buf

  • syntax: recv_udp_buf size;
  • default: 8192 buffers
  • context: srt, server

UDP socket receive buffer size, in bytes.

See the libsrt documentation of the SRTO_UDP_RCVBUF option for more details.

recv_latency

  • syntax: recv_latency size;
  • default: 120ms
  • context: srt, server

The latency on the receiving side, in milliseconds.

See the libsrt documentation of the SRTO_RCVLATENCY option for more details.

send_buf

  • syntax: send_buf size;
  • default: 8192 buffers
  • context: srt, server

Send buffer size, in bytes.

See the libsrt documentation of the SRTO_SNDBUF option for more details.

send_udp_buf

  • syntax: send_udp_buf size;
  • default: 65536
  • context: srt, server

UDP socket send buffer size, in bytes.

See the libsrt documentation of the SRTO_UDP_SNDBUF option for more details.

send_latency

  • syntax: send_latency size;
  • default: 120ms
  • context: srt, server

The minimum receiving latency, provided by the sender.

See the libsrt documentation of the SRTO_PEERLATENCY option for more details.

passphrase

  • syntax: passphrase expr;
  • default: ``
  • context: srt, server

Sets a passphrase for encryption, see the libsrt documentation of the SRTO_PASSPHRASE option for more details.

The parameter value can contain variables.

in_buf_size

  • syntax: in_buf_size size;
  • default: 64k
  • context: srt, server

Sets the size of the buffer used for reading data from the client.

srt map directives

map

  • syntax: map string $variable { ... }
  • default: ``
  • context: srt

Creates a new variable whose value depends on values of one or more of the source variables specified in the first parameter.

See the documentation of the map directive of the nginx stream module for more details.

map_hash_max_size

  • syntax: map_hash_max_size size;
  • default: 2048
  • context: srt

Sets the maximum size of the map variables hash table.

map_hash_bucket_size

  • syntax: map_hash_bucket_size size;
  • default: 32|64|128
  • context: srt

Sets the bucket size for the map variables hash table.

srt log directives

access_log

  • syntax: access_log path format [buffer=size] [gzip[=level]] [flush=time] [if=condition];
  • default: off
  • context: srt, server

Sets the path, format, and configuration for a buffered log write.

See the documentation of the access_log directive of the nginx stream module for more details.

log_format

  • syntax: log_format name [escape=default|json|none] string ...;
  • default: ``
  • context: srt

Defines a log format.

See the documentation of the log_format directive of the nginx stream module for more details.

open_log_file_cache

  • syntax: open_log_file_cache max=N [inactive=time] [min_uses=N] [valid=time];
  • default: off
  • context: srt, server

Defines a cache that stores the file descriptors of frequently used logs whose names contain variables.

See the documentation of the open_log_file_cache directive of the nginx stream module for more details.

srt proxy directives

proxy_pass

  • syntax: proxy_pass address;
  • default: ``
  • context: srt, server

Sets the address of the proxied server.

proxy_connect_timeout

  • syntax: proxy_connect_timeout timeout;
  • default: 60s
  • context: srt, server

Defines a timeout for establishing a connection with a proxied server.

proxy_timeout

  • syntax: proxy_timeout timeout;
  • default: 10m
  • context: srt, server

Sets the timeout between two successive read or write operations on client or proxied server connections. If no data is transmitted within this time, the connection is closed.

proxy_buffer_size

  • syntax: proxy_buffer_size size;
  • default: 64k
  • context: srt, server

Sets the size of the buffer used for reading data from the proxied server.

proxy_protocol

  • syntax: proxy_protocol on | off;
  • default: off
  • context: srt, server

Enables the PROXY protocol for connections to a proxied server.

proxy_header

  • syntax: proxy_header expr;
  • default: ``
  • context: srt, server

Defines a string that is sent to the proxied server before any data received over SRT.

The parameter value can contain variables.

srt set misc directives

set_decode_base64

  • syntax: set_decode_base64 $dst src;
  • default: ``
  • context: srt

Performs base64 decode of the value of the second argument, and assigns the result to the variable specified in the first argument.

set_decode_base64url

  • syntax: set_decode_base64url $dst src;
  • default: ``
  • context: srt

Performs url-safe-base64 decode of the value of the second argument, and assigns the result to the variable specified in the first argument.

set_aes_decrypt

  • syntax: set_aes_decrypt $dst base64_key base64_iv src;
  • default: ``
  • context: srt

Performs AES-256-CBC decryption of the value of the last argument, using the supplied key/iv, and assigns the result to the variable specified in the first argument.

stream srt proxy directives

srt_proxy_pass

  • syntax: srt_proxy_pass address;
  • default: ``
  • context: stream, server

Sets the address of the proxied server.

srt_proxy_connect_timeout

  • syntax: srt_proxy_connect_timeout timeout;
  • default: 60s
  • context: srt, server

Defines a timeout for establishing a connection with a proxied server.

srt_proxy_timeout

  • syntax: srt_proxy_timeout timeout;
  • default: 10m
  • context: srt, server

Sets the timeout between two successive read or write operations on client or proxied server connections. If no data is transmitted within this time, the connection is closed.

srt_proxy_buffer_size

  • syntax: srt_proxy_buffer_size size;
  • default: 64k
  • context: srt, server

Sets the size of the buffer used for reading data from the proxied server.

srt_proxy_stream_id

  • syntax: srt_proxy_stream_id expr;
  • default: ``
  • context: srt, server

Sets the SRT stream id, see the libsrt documentation of the SRTO_STREAMID option for more details.

The parameter value can contain variables.

srt_proxy_passphrase

  • syntax: srt_proxy_passphrase expr;
  • default: ``
  • context: srt, server

Sets a passphrase for encryption, see the libsrt documentation of the SRTO_PASSPHRASE option for more details.

The parameter value can contain variables.

Embedded Variables

Core

  • binary_remote_addr - client address in a binary form, the length of the value is always 4 bytes for IPv4 addresses or 16 bytes for IPv6 addresses
  • bytes_received - number of bytes received from the client
  • bytes_sent - number of bytes sent to the client
  • connection - connection serial number
  • hostname - host name
  • msec - current time, in seconds with milliseconds resolution
  • nginx_version - nginx version
  • peer_version - libsrt version of the remote peer, see the libsrt documentation of the SRTO_PEERVERSION option for more details.
  • pid - PID of the worker process
  • protocol - protocol used to communicate with the client, always evaluates to SRT
  • remote_addr - client address
  • remote_port - client port
  • server_addr - the address of the server which accepted the connection
  • server_port - the port of the server which accepted the connection
  • session_time - session duration, in seconds with a milliseconds resolution
  • status - session status
  • stream_id - SRT stream id, see the libsrt documentation of the SRTO_STREAMID option for more details.
  • time_iso8601 - local time, in ISO 8601 standard format
  • time_local - local time, in the Common Log Format

Upstream

  • upstream_addr - the IP address and port of the upstream server
  • upstream_bytes_received - number of bytes received from the upstream server
  • upstream_bytes_sent - number of bytes sent to the upstream server
  • upstream_connect_time - time to connect to the upstream server, in seconds with millisecond resolution
  • upstream_first_byte_time - time to receive the first byte of data, in seconds with millisecond resolution
  • upstream_session_time - session duration, in seconds with millisecond resolution

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-srt.