Merge from release-3.1.3 into master...

libraries/lib-ffmpeg-support/FFmpegFunctions.cpp

libraries/lib-ffmpeg-support/FFmpegFunctions.h

src/AdornedRulerPanel.cpp

src/FFmpeg.cpp

src/PlaybackSchedule.cpp

src/ProjectAudioIO.cpp

src/ProjectAudioIO.h

src/ProjectSettings.cpp

src/ProjectSettings.h

src/toolbars/TranscriptionToolBar.cpp

src/tracks/ui/Scrubbing.cpp