A denial of service in the subtitle decoder in FFmpeg 3.2 and 4.1 allows attackers to hog the CPU via a crafted video file in Matroska format, because handle_open_brace in libavcodec/htmlsubtitles.c has a complex format argument to sscanf.
"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2019-9721.json"