Initial implementation of Text Source, displaying free text or subtitle file. support for Pango font description and formatting tags via gstreamer textoverlay plugin. Saving and loading in XML, GUI for creation (in patterns) and for editing.
Allows looking for audio streams in media files (settings) and enabling / disabling audio for each MediaPlayer individually. Control of volume per media, saving in session file.
StreamSource now have the option 'restart on deactivation' like MediaPlayer. This option is saved in XML (added Visitors for Stream and StreamSource). The GUI is added as sub-menu in play bar (like for MediaPlayer). Some StreamSource subclasses needed to be fixed to allow this feature (e.g. MultiFileSource).
Enable playing and seeking into a timeline on a media player that loaded an image. Timeline sets a duration (end) and is saved/loaded. Add a gstreamer imagefreeze element in the pipeline to simulate a playable stream. Distinction must be made between 'isImage' (what was loaded) and 'singleFrame' (what is in the pipeline). GUI is added and customized with menu and dialog.
Change implementation of gst pipeline in MediaPlayer to use gstreamer playbin. This makes everything works more smoothly (including instant rate change). This also opens the possibility to allow audio mixing. Other bugfixes include set play speed rate at start, add video effects on reopen media player.
Enable use of a source as mask for another source. Improved Mask mechanism in Source class, with various flags for update of source (avoid repeated mask update (GPU costly). Using SourceLink to link source to mask (improved robustness of SourceLink).
As in update of Mixer manager, failed sources are managed in update of SessionSources. RenderSources that fail are re-created. Attach/Detach/Attached of sources functions is unified between Session and Mixer.
2 new callbacks (PlayFastForward, PlaySpeed), modified Seek callback to take target time in seconds (instead of ratio of duration). Integrating this in Input Mapping GUI and Session saving.
Session contains a set of 'Batch' that are created in the Player (renamed from PlayGroups). Session InputCallback can now target either a Source or a Batch, using std::variant (new type Target). Input Mapping reacts to input to create callbacks to a target, either a single source (as before) or to a Batch (multiple sources).
