Threads delay killer bug
Change to Frame threading mode created regressions for users with slow cpus/complex codecs.
Core deals with decoder delay on the first call to timestamp conversion.
For that reason, if a decoder outputs data really late, but another decoder calls timestamp conversion earlier (typically audio), the core will set the conversion pcr-delay to the lowest one. It then will break definively the other stream with invalid conversion.
This can be checked with Hikvision HEVC which outputs really late (9th block push) with 10 threads.
https://forum.videolan.org/viewtopic.php?f=14&t=150375&p=495321#p495321
Workaround: This does not happen when avcodec is in low-delay (also disables threading), but it only hides the design issue.