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VSE bug – Inability to enter or change numerical data in fields
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Description

Windows 7 Professional 64-bit SP1
Nvidia GeForce GTX 760

Broken: Blender 2.75a ...up to and including current version... 2.77 rc2

Description: Under certain circumstances the numerical buttons in the Video Sequence Editor will refuse to accept value changes.

To produce this bug do as follows:

Open Blender to default scene of cube.

In camera properties/shading set alpha from ‘Sky’ to ‘Transparent’.

Go into VSE and add a movie strip.

Now add default scene strip on top of movie strip.

Set scene strip to ‘Alpha Over’.

With scene strip still selected go to frame sixty (60) on timeline. (exact frame not important)

In the Edit Strip section on the right of the channel window set a keyframe for Opacity.

Once this first keyframe has been set the value button will no longer want to accept changes to the numerical data. It does not matter whether one slides the numerical data with the mouse, or enters it by clicking and pressing the ‘enter’ key. The numerical data will always want to reset itself to the value of the first keyframe pressed.

Going to a different frame and attempting to enter other numerical data into the value button gives the same results. [ Workaround: The value button(s) will, however, still accept a new keyframe and the value of that keyframe can then be edited in the graph editor. ]

Once this odd behaviour has started, the same thing will occur with the other channels. In either the movie strip or the sound strip, values in the editing fields can be changed successfully until a first keyframe has been entered for some property. After that, the field will no longer want to change.

Please note: This example used the ‘Opacity’ value, but almost any animatable value button will trigger the same behaviour.

Also, it does not matter which strip one selects first (scene, sound or movie clip) the same thing will happen.

Details

Type
Bug

Event Timeline

Ignatz (ignatz) added a project: BF Blender.
Ignatz (ignatz) set Type to Bug.
Ignatz (ignatz) added a subscriber: Ignatz (ignatz).
Ignatz (ignatz) created this task.
Ignatz (ignatz) raised the priority of this task from to Needs Triage by Developer.
Joshua Leung (aligorith) closed this task as Archived.
Joshua Leung (aligorith) claimed this task.

This is a well known bug that we'd like to fix, but doing so would require recoding a few things in the Sequencer and in the way that Blender evaluates data (i.e. depsgraph related stuff). In short, this can only be fixed when we fix things up so that data can be evaluated in the background on a separate copy of any datablocks used.

The main problem here is that whenever an update for the sequencer gets triggered/evaluated (and a scene strip is involved), it will go through and re-evaluate Blender's datablocks so that they can be used for rendering the state in the scene strip. Now, if you've got unkeyed values on any properties, and those properties are part of the scene being referenced, this re-evaluation of the scene datablock and related stuff (via the scene strip) will cause the unkeyed values to get overwritten by whatever the FCurves currently do at that frame (i.e. the value prior to you trying to modify it). Hence, the unkeyed values get lost, and it all appears to be locked up/unchangeable.

(Editing the FCurves though is fine, as the FCurves don't change shape just because you re-evaluate the current frame or some other frame).

So, current resolution is: Bug, but can't fix. Pending Depsgraph-Overrides/BackgroundEval work that's being planned for 2.8.