Set SRT sndbuf and rcvbuf in FFmpeg URL

Setting the socket send and receive buffer sizes in FFmpeg when using the Secure Reliable Transport (SRT) protocol is crucial for optimizing network transmission and preventing packet loss. This article provides a direct guide on how to configure the sndbuf (sender buffer size) and rcvbuf (receiver buffer size) parameters directly within your FFmpeg SRT connection URL to ensure stable streaming over high-latency or high-bandwidth networks.

SRT URL Parameter Syntax

In FFmpeg, SRT options are passed as query parameters directly inside the SRT URL. The parameters are appended to the destination address using a question mark (?) and separated by ampersands (&).

To configure the send and receive buffers, use the sndbuf and rcvbuf options. The values for these buffers are defined in bytes.

Configuration Example

Here is the standard format for setting both buffers in an FFmpeg command:

ffmpeg -i input.mp4 -f mpegts "srt://12.34.56.78:9000?sndbuf=2097152&rcvbuf=2097152"

In this example: * sndbuf=2097152 sets the send buffer size to 2,097,152 bytes (2 MB). * rcvbuf=2097152 sets the receive buffer size to 2,097,152 bytes (2 MB).

Important Usage Considerations

  1. Quote the URL: Always wrap the SRT URL in double quotes ("..."). In most command-line shells (like Bash, Zsh, or PowerShell), the ampersand (&) is a special character used to run processes in the background. Quoting the URL prevents the shell from misinterpreting the query parameters.
  2. Default Values: If not specified, SRT will use the default operating system socket buffer sizes. Manually increasing these values is highly recommended for high-bitrate 4K streams or connections with high round-trip time (RTT).
  3. System Limits: The maximum buffer size you can set is limited by your operating system’s kernel settings (for example, rmem_max and wmem_max in Linux). If you set sndbuf or rcvbuf higher than the OS limit, the system will cap it at its maximum allowed value.