How to Set FFmpeg UDP TTL and Buffer Size

This article provides a straightforward guide on how to configure the Time-to-Live (TTL) and socket buffer size parameters for UDP streaming in FFmpeg. You will learn the exact syntax and options required to control network hops, prevent packet loss, and optimize the stability of your live UDP streams.

Configuring UDP Parameters in FFmpeg

In FFmpeg, network protocols like UDP are configured by appending query parameters directly to the stream’s destination or source URL. The syntax follows a standard query string format: udp://[address]:[port]?option1=value1&option2=value2.

1. Setting the Time-to-Live (TTL)

The TTL parameter determines the maximum number of network hops a packet can take before being discarded. This is especially important in multicast streaming to prevent packets from circulating indefinitely or traveling outside the intended network segment.

To set the TTL, use the ttl option:

ttl=integer_value

For example, to set the TTL to 5:

udp://239.0.0.1:1234?ttl=5

2. Setting the Buffer Size

The buffer size parameter specifies the size of the operating system’s socket send or receive buffer in bytes. If your stream has a high bitrate, the default system buffer may overflow, causing packet drops and video corruption. Increasing the buffer size prevents this.

To set the socket buffer size, use the buffer_size option (values are in bytes):

buffer_size=integer_value

For example, to set a 10 megabyte (10,000,000 bytes) buffer:

udp://239.0.0.1:1234?buffer_size=10000000

Note: On Linux and macOS, the operating system imposes a maximum limit on socket buffers. If you request a buffer larger than the system limit (defined by sysctl net.core.rmem_max or wmem_max), FFmpeg will only allocate up to the OS-allowed maximum.

Complete Example Command

To stream an input file via UDP multicast, setting the TTL to 10 and the buffer size to 5MB, use the following FFmpeg command:

ffmpeg -re -i input.mp4 -c copy -f mpegts "udp://239.0.0.1:1234?ttl=10&buffer_size=5000000"

In this command: * -re reads the input file in real-time. * -c copy copies the streams without re-encoding to save CPU. * -f mpegts muxes the output into the MPEG transport stream format, which is standard for UDP streaming. * The URL parameters are separated by an ampersand (&) and enclosed in quotes to prevent the terminal shell from misinterpreting the special character.