Patch implements better way to control playback speed than it is
possible to do with speed effect. Speed factor property can be set in
Time panel.
There are 2 layers of control:
Option to retime movie to match scene FPS rate.
Custom speed factor to control playback rate.
Since playback rate is strip property, it is now possible to manipulate
strip as normal one even if it is retimed.
To facilitate manipulation, some functions need to consider speed factor
and apply necessary corrections to strip offset or strip start. These
corrections may need to be float numbers, so start and offsets must be
float as well.
Sound strips now use speed factor instead of pitch. This means, that
strips will change length to match usable length. In addition, it is
possible to group movie and sound strip and change speed of meta strip.
This patch adds channel region to VSE timeline area for drawing channel
headers. It is synchronizedwith timeline region. 3 basic features are
implemented - channel visibility, locking and name.
Channel data is stored in `SeqTimelineChannel` which can be top-level
owned by `Editing`, or it is owned by meta strip to support nesting.
Strip properties are completely independent and channel properties are
applied on top of particular strip property, thus overriding it.
Implementation is separate from channel regions in other editors. This
is mainly because style and topology is quite different in VSE. But
also code seems to be much more readable this way.
Currently channels use functions similar to VSE timeline to draw
background to provide illusion of transparency, but only for background
and sfra/efra regions.
Great portion of this patch is change from using strip visibility and
lock status to include channel state - this is facilitated by functions
`SEQ_transform_is_locked` and `SEQ_render_is_muted`
Originally this included changes in D14263, but patch was split for
easier review.
Reviewed By: fsiddi, Severin
Differential Revision: https://developer.blender.org/D13836
