In mpegtsmux/mpegtsmux.c function check_pending_key_unit_event() always assumes that the pending_event is upstream, which is not always the case - function mpegtsmux_sink_event() assigns an event of downstream type to mux->force_key_unit_event, which later gets passed to check_pending_key_unit_event().

In case when the actual event is downstream, parsing it as an upstream one doesn't work right, in particular it assigns wrong values to count variable. In my setup those count values were changing unpredictably or in many cases not changing in subsequent FKU events, and thus propagation of that FKU event downstream would stop.

Attached patch fixes the issue.

Please note also that there is probably an analogous problem in videoparsers/gsth264parse.c which has almost identical implementation of check_pending_key_unit_event().