ビルド

$ curl -L https://ffmpeg.org/releases/ffmpeg-4.0.2.tar.bz2 > ffmpeg-4.0.2.tar.bz2
$ tar xf ffmpeg-4.0.2.tar.bz2
$ cd ffmpeg-4.0.2/
$ vim libavformat/libsrt.c   # 469行目に h->max_packet_size = 1316; を追加
$ ./configure --enable-libsrt --enable-libx264 --enable-gpl; say 'オワッタヨ'
$ make; say 'オワッタヨ'
$ ./ffmpeg -protocols | grep srt
ffmpeg version 4.0.2 Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
  configuration: --enable-libsrt --enable-libx264 --enable-gpl
  libavutil      56. 14.100 / 56. 14.100
  libavcodec     58. 18.100 / 58. 18.100
  libavformat    58. 12.100 / 58. 12.100
  libavdevice    58.  3.100 / 58.  3.100
  libavfilter     7. 16.100 /  7. 16.100
  libswscale      5.  1.100 /  5.  1.100
  libswresample   3.  1.100 /  3.  1.100
  libpostproc    55.  1.100 / 55.  1.100
  srtp
  srt
  srtp
  srt

動作確認

先に受信側を起動（こちらはhomebrewでいれたffmpegのffplay）

ffplay -analyzeduration 100 -i 'srt://127.0.0.1:3000?mode=listener'

送信側を起動（こちらはさきほどビルドしたもの）

./ffmpeg -f avfoundation -framerate 30 -i "0:" -c:v libx264 -pix_fmt yuv420p -profile:v baseline -level 1 -preset ultrafast -tune zerolatency -x264opts bitrate=2000 -an -f mpegts 'srt://127.0.0.1:3000'

メモ

https://trac.ffmpeg.org/ticket/7187 でthe mss option should be used per mss=1316 So not a bug.とあったのでsrt://127.0.0.1:3000?mss=1316も試してみたけど、やはりSRT.c: LiveSmoother: payload size: 15040 exceeds maximum allowed 1316といわれてしまう