MLT - v7.4.0 released

Dec 19, 2021

This main highlight of this version is property animation for avfilter!

Added more constructors and assignment operators in C++ wrapper:
- Mlt::Filter::Filter(Mlt::Filter*)
- Mlt::Link::Link(Mlt::Link*)
- Mlt::Link::Link(Mlt::Service&)
- Mlt::Link::Link(Mlt::Link&)
- Mlt::Link::Link(Mlt::Link const&)
- Mlt::Link::operator=(Mlt::Link const&)
- Mlt::Service::Service(Mlt::Service*)
Fixed serialized animation in mlt_animation_serialize_cut_tf() and mlt_animation_serialize_cut() to include a trailing keyframe value.

Added property animation for avfilter filters.
This only works for numeric parameters, but many libavfilter options that have a type string are actually numeric in nature but accept a string expression.
Added rotate property to avformat producer to override orientation.
Changed jackrack module to silence false LADSPA plugin loading errors.
Fixed a crash in the oldfilm filter when using preview scaling.
Fixed timeremap link distorts audio when speed is zero.
Added nautical mile and knot units of measure to the gpstext filter.
Fixed full range color handling with embedded tractor (e.g. same track transition).
Fixed device capture in avformat producer regression in version 7.2.0.
Fixed a crash in the matte transition.