rtsp-simple-server/docs/2-features/07-remuxing-reencoding-compression.md

Re-encoding

To change the format, codec or compression of a stream, use FFmpeg or GStreamer together with MediaMTX. For instance, to re-encode an existing stream, that is available in the /original path, and publish the resulting stream in the /compressed path, edit mediamtx.yml and replace everything inside section paths with the following content:

paths:
  compressed:
  original:
    runOnReady: >
      ffmpeg -i rtsp://localhost:$RTSP_PORT/$MTX_PATH
        -c:v libx264 -pix_fmt yuv420p -preset ultrafast -b:v 600k
        -max_muxing_queue_size 1024 -f rtsp rtsp://localhost:$RTSP_PORT/compressed
    runOnReadyRestart: yes