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Video Editing: Preview shows previously cached frame after Hard Cut and Extend
Confirmed, NormalPublicBUG

Description

System Information
Operating system: Win 10, 64bit
Graphics card: no

Blender Version
Broken: (v 2.82a) and also (v 2.83 Alpha, Date 2020-03-18 17:16, Hash c9c08dc7c873)

Short description of error
I often freeze a sequence, by hard cut, move the right part and extend the left part.
(1234) -> hard cut -> (12|34) -> move right -> (12|--|34) -> extend left -> (1222|34)

Sometimes the preview then shows a previously cached frame at the beginning of the frozen sequence, resulting in a visible backward motion.
Correct Preview: (1222|34)
Wrong Preview: (1232|34)

Exact steps for others to reproduce the error
In the Video Editor:
Step 0: Add a scene or image sequence with 4 frames (1234) or open the attached file

.
-> Preview shows Frame 1
Step 1: Type the right arrow key > twice
-> Preview shows Frame 3
Step 2: Type Shift-K to Hard Cut the strip (12|34) into a new left strip and a new right strip.
-> Preview shows Frame 3
Step 3: Use the mouse to Delete or move away the right strip (34).
-> Preview shows nothing
Step 4: Pull the arrow of the left strip (12) to Extend it by two or more frames.
-> Preview shows Frame 3 (but it should show Frame 2)
Step 5: Press the arrow keys to switch trough the frames
-> Preview shows the frames (1232) (but it should show the frames (1222))
Step 6: Clear cache (Move the strip, or save and reopen the file)
-> Preview shows the frames (1222)

Note 1: Error MAY NOT occur, if during Step 1, the left arrow key < was pressed.
Note 2: Error MAY NOT occur, if during Step 1, the Play Animation button was pressed.
Note 3: Error DOES occur, if in Step 1, the mouse is used to reach Frame 3 (as far as I have tested it)
Note 4: Error DOES NOT occur, if the time cursor is moved between Step 2 and Step 3.
Note 5: Error DOES occur, if the initial scene has a different number of frames.
Note 6: Error DOES occur, if the Hard Cut is at a different position.
Note 7: Error DOES NOT show in the rendered animation
Note 8: I think, in one case, there were multiple incorrect frames, like a flicker (1234) -> (12323232|34) instead of -> (12222222|34), however, I could not reproduce.

Picture 1: Correct Preview

Picture 2: Wrong Preview

Event Timeline

Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.Mon, Mar 23, 3:18 AM
Richard Antalik (ISS) changed the subtype of this task from "Report" to "Bug".

Note 8: I think, in one case, there were multiple incorrect frames, like a flicker (1234) -> (12323232|34) instead of -> (12222222|34), however, I could not reproduce.

I had one similar report to this, I think this bug made it to final render. I wasn't able to reproduce though. I will look at code and see if there is some type conversion or anything, that could caused this, but reproducible case would help a lot.. Can you tell at what framerate did this happen?

95% sure, it was 24fps for both scenes (video editor and animation source).

Note 8: I think, in one case, there were multiple incorrect frames, like a flicker (1234) -> (12323232|34) instead of -> (12222222|34), however, I could not reproduce.

Please don't waste too much time on Note 8. I was wildly experimenting with scripts and render settings that also caused all sorts of flickers. So, I'm only 50% sure, that the Note 8 flicker was caused by a hard cut.
I suggest, find the reproducible bug, and then consider for 10 minutes, if the reproducible bug might also cause some kind of flicker.

Do you have a report number of this similar report? Maybe it helps me to trace my steps back.

Best
Gabriel

95% sure, it was 24fps for both scenes (video editor and animation source).

Note 8: I think, in one case, there were multiple incorrect frames, like a flicker (1234) -> (12323232|34) instead of -> (12222222|34), however, I could not reproduce.

Please don't waste too much time on Note 8. I was wildly experimenting with scripts and render settings that also caused all sorts of flickers. So, I'm only 50% sure, that the Note 8 flicker was caused by a hard cut.
I suggest, find the reproducible bug, and then consider for 10 minutes, if the reproducible bug might also cause some kind of flicker.

Sure.

Do you have a report number of this similar report? Maybe it helps me to trace my steps back.

T72683: Blender VSE 2.8 speed control doesn't match render
If it's same issue it would probably be linked to speed control and possibly only when it is used to stop or pause input strip, but technically it could happen even after hard cut

Best
Gabriel

Gabriel (gabi2002) added a comment.EditedMon, Mar 23, 5:30 PM

I retraced the error steps of T72683.
Adding the speed effect made my bug worse.
However it only affects the preview. Rendered frames are fine. So, I couldn't reproduce the problem reported in T72683.

To ease reproducing, I left Multiply Speed set to 1 (no change)

Soft cut, add speed effect

  • Step 0 Add Scene: 123456789
  • Step 1 cut strip: 1234|56789
  • Step 2 delete: 1234 (expected result, I leave cursor at frame 5)
  • Step 3 add speed effect: 1234 (expected result, I leave cursor at frame 5)
  • Step 4 extend: 123456789 (expected result, I leave cursor at frame 5)
  • Step 5 preview: 123486789

Soft cut, move cursor, add speed effect
This third version of my bug is similar, to what I remembered in Note 8. However, Note 8 did not involve a speed effect.

  • Step 0 Add Scene: 123456789
  • Step 1 cut: 1234|56789
  • Step 2 delete: 1234¦ (expected result, I leave cursor at frame 5)
  • Step 2a move Cursor (hit right arrow key 2x) 1234__¦
  • Step 3 add speed effect: 1234__¦ (expected result, I leave cursor at frame 7)
  • Step 4 extend: 123456789 (expected result, I leave cursor at frame 7)
  • Step 5 preview: 123456889

stretch speed controlled strip

  • Step 0 Add Scene: 123456789
  • Step 1 add speed effect: 123456789 (expected result, I leave cursor at frame 1)
  • Step 2 move cursor to frame 2
  • Step 3 shorten strip
  • expected result 147
  • preview result 127

Best
Gabriel