The flv_write_packet function in libavformat/flvenc.c in FFmpeg through 2.8 does not check for an empty audio packet, leading to an assertion failure.
https://www.debian.org/security/2019/dsa-4449
https://usn.ubuntu.com/4431-1/
https://usn.ubuntu.com/3967-1/
https://seclists.org/bugtraq/2019/May/60
https://lists.debian.org/debian-lts-announce/2019/05/msg00043.html
https://github.com/FFmpeg/FFmpeg/commit/d8ecb335fe4852bbc172c7b79e66944d158b4d92
https://github.com/FFmpeg/FFmpeg/commit/6b67d7f05918f7a1ee8fc6ff21355d7e8736aa10