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IDProjectCategoryView StatusDate SubmittedLast Update
0002403KdenliveFile Loadingpublic2011-11-12 06:322011-12-08 22:51
Assigned Toj-b-m 
Platformx86_64OSLinuxOS Version3.1.0
Product Version0.8.2 
Target VersionFixed in Version0.8.2.1 
Summary0002403: concurrent proxy generation segfaults
DescriptionI have been trying to limit kdenlive to one cpu on my system to eliminate a crash that I have been trying to find.

So, even when confined to one cpu kdenlive still tries to generate proxies while loading the clips. Once all the clips are loaded, it starts another proxy generator.

I am suspecting that there is a concurrency issue between the two ffmpeg processes that are running, but I have found no way of limiting proxy generation to only one.

Steps To ReproduceLoad a lot of clips, watch system.
Additional InformationOne other observation:
Thumbnail generation does not start until proxy generation is completed. Is this normal? Are thumbnails created from the proxies, or from the original footage?
TagsNo tags attached.
Build/Install Method(select)
Attached Files

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-  Notes
yellow (reporter)
2011-11-12 08:31
edited on: 2011-11-12 08:44

This report seems to be same problem as No. 002388?

Not sure whether to respond here or on 002388 now. :-)

I think this maybe an Intel processor handling related problem, as I can easily load 200+ HD movs from my Canon 550D and generate proxies (for a new project, pre 8.2 projects giving me real pain not crashing though) on 64bit Ubuntu with single Sempron 3400 and 2GB RAM I have no issues, system monitor shows one instance of ffmpeg.

On a dual processor Xeon with hyperthreading enabled as discussed in 002388 on each and 2GB RAM I get 4 ffmpeg instances and crashes after so long, yet switching hyperthreading off I get stability and 2 ffmpeg instances running.

So greater than one instance of ffmpeg does not crash kdenlive for me, but having hyperthreading on is an issue.

Have you simply tried turning hyperthreading off in your bios, just as a test, not sure if i3, i5 & i7's even have hyperthreading these days, still on old hardware. :-(

Ok, Wikipedia [^] suggest that Intel recommend switching off HT for OS's that are not optimised for it.

evorster (reporter)
2011-11-12 08:41

Well, this ticket is related to 002388.
However, I would like to be able to limit the amount of concurrent proxy generators running in any case, as I would then be able to do editing while the clips load.

Just FYI, the Core architecture does not do hyperthreading. In stead, it has multiple cores on the same die.

I suspect that under cgroups with multiple CPU's and DDR3 I am hitting the FSB pretty hard, and with highly optimized hand-coded asm in ffmpeg I might be hitting a concurrency problem specific to Intel hardware.

I am not seeing the crash when I limit kdenlive to one CPU only, so that is at least a step in the right direction in regards to the crash. However, being able to limit proxy generator instances seem to be a more robust solution to my problem, rather than disabling hardware features system-wide.
yellow (reporter)
2011-11-12 08:49

Yes absolutely, only temporary measure to at least be able to work with kdenlive.
evorster (reporter)
2011-11-12 09:01

I found that putting kdenlive in a cgroup and limiting that cgroup to one cpu achieves the same effect. Unfortunately, that means kdenlive runs slower.

Funnily enough, this crash is only on proxy generation.

Kdenlive could be used without proxies, with the HD sources transcoded into DNxHD ( scarily huge amounts of disk needed ) or one could limit kdenlive to one CPU for proxy generation, save the project, and then load up kdenlive with all system resources available for editing and rendering. ( a pain )
I would prefer an configuration option to limit proxy generation instances.
j-b-m (administrator)
2011-11-13 23:45

I just committed a fix (rev. 6c74a57 in master), now you can limit the number of threads for proxy creation, in the Settings dialog > Environment. By default it is limited to 2 threads, but you can set it to 1.

Please let me know if it solves your problem.
evorster (reporter)
2011-11-14 04:57

git pull says I am already up to date, and I don't see this fix.
evorster (reporter)
2011-11-14 05:02

Ah, I was synchronised with sourcefourge git. I am now synched with's git.

evorster (reporter)
2011-11-14 19:38

I can confirm that setting the proxy generator instances down to 1 works around this issue. Thanks for the great support.

- Issue History
Date Modified Username Field Change
2011-11-12 06:32 evorster New Issue
2011-11-12 08:31 yellow Note Added: 0007547
2011-11-12 08:41 yellow Note Edited: 0007547 View Revisions
2011-11-12 08:41 evorster Note Added: 0007548
2011-11-12 08:44 yellow Note Edited: 0007547 View Revisions
2011-11-12 08:49 yellow Note Added: 0007549
2011-11-12 09:01 evorster Note Added: 0007550
2011-11-13 23:45 j-b-m Note Added: 0007568
2011-11-13 23:45 j-b-m Assigned To => j-b-m
2011-11-13 23:45 j-b-m Status new => feedback
2011-11-14 04:57 evorster Note Added: 0007569
2011-11-14 04:57 evorster Status feedback => assigned
2011-11-14 05:02 evorster Note Added: 0007570
2011-11-14 19:38 evorster Note Added: 0007576
2011-11-14 19:39 j-b-m Status assigned => resolved
2011-11-14 19:39 j-b-m Fixed in Version =>
2011-11-14 19:39 j-b-m Resolution open => fixed
2011-12-08 22:51 j-b-m Status resolved => closed

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