Vulnerability is in libheif's HEIF sequence parser
(Track::init_sample_timing_table / Track::load in
libheif/sequences/track.cc). This sequence / ISOBMFF track parsing was
added in v1.20.0; v1.19.8 — the version we ship — has no sequences/
directory and no init_sample_timing_table (verified: no such file or symbol
in the v1.19.8 source), so the vulnerable code is not present.