"Proxy" Clips for HD editing


I'm using Kdenlive with clips in 1080P from my camcorder, but previewing is very slow (frames drop, etc.).

So I was wondering if it was possible to use a "proxy" clip (very downscaled), and tell Kdenlive to use it for editing, but keep the 1080P original file for export.

Just an idea ...



I have problems using proxy clips with kdenlive from sunab's ppa repo on Kubuntu 11.10 beta 2 64bit. When I enable proxies in the project settings and switch on the proxy for my full HD 1080p material I only get the error message "proxy crashed" (actually, the localized variant of this message). For one or two short 20 secs or so clips I got proxies, but otherwise only crashed proxies.

Also, while my i5 quad core is more or less idle when playing fullHD footage, kdenlive often enters "slide show mode" when repositioning the current position from which to play the video. I've played around with one or three threads in kdenlive, but the result is the same. However, the system is perfectly capable of playing multiple fullHD videos at the same time, even with scaling and transparency, so the CPU and system power should be reasonable sufficient.

Any help or clues?

In some thread, which I unfortunately can not find again, ddennedy has written some lines about comparing a movie player with the preview monitor in Kdenlive.

Kdenlive does far more work per frame than the player does. That is why the output is (and possibly will stay) choppy. This was the reason to introduce proxy clips.

As for the choppy output: so far, it appears that kdenlive only uses a single core of my quadcore when rendering, regardless of whether I set 1 or 3 threads in the settings.

And for the proxy: I would like to use them if only they would work.

I am not a developer of Kdenlive, but both features are quite new and will grow in stability with the next release. Right now I am working with SD material, so I do not need more than one decode thread and never used that feature.

When rendering, the current release of Kdenlive available for Arch Linux (seems to be a snapshot from 2011-09-22) utilizes the number of threads I have selected in the rendering dialog. Kdenlive does not use one core for two threads for all the rendering. The active core seems to change if a unit of work is done and the program requests the cpu again.

For your proxies crashing you can try a different proxy encoding profile. If you go into Settings -> Configure kdenlive you can create extra profiles. I use this: -f avi -acodec copy -vcodec mjpeg -s 480x270 -b 4000k for my Canon DSLR sources for example.

Now I have to look as to why a project I was working on last night now crashes kdenlive outright tonight after an update from sunabs PPA half an hour ago. :-(

Cutting edge can be a bit painful. :-)

Thank you for the hints, I will try another profile this evening. While I really don't need FullHD footage, I'm "stuck" with it as I have a cute, small HD Hero cam that I put on my head during diving. Unfortunately, due to constraints of the cam's optical system in conjunction with a modified cam diving housing I have to shoot in 1080p FullHD instead of 720p HD. Otherwise, I get vignetting. Of course, FullHD footage of "dirt diving" in European lakes is kind of snotty. ;)

As for the multi-threading: of course, the OS scheduler is responsible for arranging threads to cores and if threads don't require much resources I may well end up with the scheduler putting all three threads on the same CPU for some affinity reasons.

I've now solved my problem with proxy clips crashing during creation: I had to install libavcodec-extra-53 (the number may change depending on your distribution version). Then I created a proxy profile (I called mine "HD MPEG") with the following options:

-f mpegts -acodec libmp3lame -ac 2 -ab 92k -ar 48000 -vcodec mpeg2video -g 5 -deinterlace -s 1280x720 -b 9000k

This put my quad core to work, finally. :)