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Prefetch frames does not seem to take effect on playback
Closed, InvalidPublic


System Information
Mac OS X 10.9.4

Blender Version
Broken: 2.71

Short description of error
Editing a multi-strip project on VSE, I am not able to playback smoothly the sequence.

No matter if I change the value in Blender preferences (System - Seuqnecer/Clip Editor: Prefetch Frames), the playback hangs and even Blender become unresponsive.

By the way, the documentation ( says that there is a limit on "System - Sequencer/Clip Editor" values. If the documentation is updated and this is still applicable, I think the controls of UI should limit the numbers. Should I open another bug for this UI issue?



Event Timeline

Jonata Bolzan (jonata) set Type to Bug.
Jonata Bolzan (jonata) created this task.
Jonata Bolzan (jonata) raised the priority of this task from to Needs Triage by Developer.
Sergey Sharybin (sergey) triaged this task as Normal priority.Jul 28 2014, 12:47 PM
Antony Riakiotakis (psy-fi) lowered the priority of this task from Normal to Needs Information from User.Aug 4 2014, 1:14 PM

Quick test with two strips here looks OK...I'd like a test file to investigate if possible.

Well, it is not that hard to reproduce. Just add a lot of strips with common effects like alpha over. The link is for a screen record of some strips playing with some video. The FPS goes to 4-7 - definitely not smooth - and you can note that when you move a strip and play, you can see... how can I say... "residual" frames that, as I understand, is a consequence of blender not pre-"fetching" the frames.

Thanks for the attention.

This looks like latency due to computation time rather than a hang. Scaling and translating an image just takes time. This is normal.

I see. So, what is "prefetch" for?

Prefetch fetches the frames of the movie itself in memory, it doesn't influence computation time due to transform operations. In the uploaded video you can clearly see that the delay occurs only while those transforms are active, not due to the movie itself.