Bug 407810

Summary:	Preview lags on transitions, etc.
Product:	[Applications] kdenlive	Reporter:	Andrey <megester>
Component:	Rendering & Export	Assignee:	Jean-Baptiste Mardelle <jb>
Status:	RESOLVED FIXED
Severity:	normal	CC:	fritzibaby
Priority:	NOR	Flags:	fritzibaby: Translation_missing+
Version First Reported In:	19.04.1
Target Milestone:	---
Platform:	Debian testing
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Andrey 2019-05-21 19:46:40 UTC

SUMMARY
When editing 4K footage, the playback of a preview zone often gets stuck for a couple of seconds when it switches from a clip to clip.

STEPS TO REPRODUCE
1. Add several 4K AVC (70 Mbps or more) clips to the timeline
2. Select ProRes as the preview profile (because MJPEG selected by default is very slow)
3. Mark all the timeline as a preview zone and render it
4. Play it back from the beginning

OBSERVED RESULT
The playback often gets stuck for a while at transitions as if every clip is still being read from the disk and it pre-caches something.

EXPECTED RESULT
I thought that preview means it is all now pre-rendered and nothing is being read from the original sources nor any processing being done.

ADDITIONAL INFORMATION
I used the latest AppImage.

Comment 1 emohr 2021-03-04 19:03:01 UTC

Please try with the current Kdenlive AppImage version 20.12.2 https://download.kde.org/stable/kdenlive/20.12/linux/

There is the possibility to scale the preview for better playback (Monitor, bottom left, field with 1:1).

Comment 2 Andrey 2021-03-04 20:27:14 UTC

(In reply to emohr from comment #1)
> Please try with the current Kdenlive AppImage version 20.12.2
> https://download.kde.org/stable/kdenlive/20.12/linux/
> 
> There is the possibility to scale the preview for better playback (Monitor,
> bottom left, field with 1:1).

Just checked it out - it now seems to work fine. Actually I've moved to a proxy + downscaled monitor approach at some time since opening this ticket, since it gives instant results when tweaking parameters. In fact, on a decent machine, the preview tool is now mostly redundant, even for quite complex effects.

Comment 3 emohr 2021-03-05 15:27:00 UTC

Thank you for the feedback and contribution. Glad to hear it works.