Preview rendering in timeline
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This is a very important option. It has to be possible to review the timeline in a smooth way and at full resolution before to export.
For this reason all the professional video editor applications have the option for rendering effects on the timeline. In Lightworks timeline rendering is one of the features you have to pay!
The proxy clips feature can help but you can't use compressed clips for colors correction or for keying.
In avid and FCP you can turn ON / OFF an RT feature. When the button is turned on the app works as Kdenlive is working at today. When RT is turned OFF you have to render all the part of the timeline the hardware is not able to playback without dropping frames.
Cinelerra has, since more than 10 years, an interesting feature called "background rendering" which was recently introduced in AVID media composer 8.2 and in FCPX. It renders automatically all the areas you need to calculate while you're working.
The realtime playback Kdenlive has today is more similar to the one we can find in compositing software not in video editors porgrams.

Related Objects

Mentioned In
R158:b94bfa96ec74: Clicking on timeline preview while it is running aborts rendering Ref: T1949
R158:3578ebcccf31: Fix timeline preview rendering on 24fps projects CCBUG: 364106 Ref: T1949
R158:b6fd9fbc11a1: integrate track hide/mute to undo system Ref: T1949
R158:c41fdf5d2c33: Timeline zone fine tuning Ref: T1949
R158:c5313dcc7738: Multi-level undo/redo for timeline previews (5 levels max), untested on large…
R158:6dcb4658cdae: Fix timeline preview button disappearing on restart Ref: T1949
R158:4b6a75259980: Make timeline toolbar configurable Move back zoom slider and timeline config…
R158:fb02b5b1d20a: On document opening, if a timeline preview file is more recent than the…
R158:4234e1836252: Correctly invalidate timeline preview on track hide and effects Ref: T1949
R158:1799b44b560c: Fix a few bugs in timeline preview, add support for undo (only 1 step…
R158:c8b102be5b60: Automatic timeline preview profile selection, can be forced in project…
R158:f8c140c2c5a5: Add stop timeline preview render action Ref: T1949
R158:a60f707493d9: Add automatic timeline preview Ref: T1949
R158:9040da7eebd1: Timeline preview render: put small progress bar inside start button Ref: T1949
R158:67c5e25c5d74: Configurable encoding params for timeline preview. Must be set in: Kdenlive…
R158:58fb4f817344: Fix Insert Zone broken Fix Effect state & Clip status not invalidating…
R158:2d58c5328b11: Change rendered preview bar to green Ref: T1949
R158:af45b4916ad4: Preliminary implementation of timeline preview rendering Available in…
Mentioned Here
T2582: file caching policy
T1239: Icon theme management

Just one suggestion about it:
I guess you can choose what to render without any color bar which alerts you about what you have to do (every PC hardware is different so every machine is able to playback in a different way the effects and the compositing). If you find an area where your PC is not able to playback the effects or the compositing in RealTime you can just select that zone and render it. Once the rendering is done (maybe in the background so you can continue to work on other areas of the project) a green line could appear on the timeline bar just for reminding you that the area was rendered for timeline preview. The rendered area could be composed of a series of very small files (maybe they could be long just as one GOP) so if you change something in that area Kdenlive has to re-render just the changes.

mardelle added a comment.EditedMay 16 2016, 9:13 PM

I just committed a preliminary version of this feature for testing. Here is how it works:

1- you select a timeline zone
2 - Timeline menu > Timeline Preview Render

This will start a background rendering (a progress bar is shown in status bar). The rendering process currently creates video files of 200 frames. Once a chunk is created, a yellow bar appears in timeline ruler (see screenshot) to indicate that the zone is rendered. Since this feature creates 200 frames chunks, the preview render zone is sometimes larger than timeline selection. Moving, deleting or inserting a clip should correctly invalidate the concerned chunks and the yellow bar will disappear.

Currently not implemented / broken:

  • editing /adding / removing transitions will not invalidate the preview render (will be easy to add)
  • no way to stop the background preview rendering
  • conflicts with the "split effect compare" feature of timeline
  • saving / loading the project does not handle the feature
  • preview files are never deleted

I have not yet really tested if it does really speed up playing in complex timeline.
Before going further, I would like to have some feedback.

Feedback based on your declarations (the new version is not yet in the master PPA)

On the rendering process length, you'll be able to work later. (I suggest a series o very short files that we can substitute when we have to re-render the modified part)
I think the green color is better than the yellow because it communicates: "Green light".
Since the feature has a fixed length we have not to worry about side effects linked to this.
It's a correct behavior if the bar disappears once we have changed the rendered area on the timeline. I guess that in the future, when it'll be possible to control the length of the rendering and we'll have a series of shorter files, that just in the parts we have to render again the yellow (or maybe green ;)) bar will disappear.

  • If it's easy to do it's ok
  • Is there not a chance to show a button for kill the rendering process in the status bar near to the progress bar?
  • I don't know why in the latest version I installed I can't find the "Split view" effect. If I well remember it was a filter. I know this feature cost you time but is it not possible to implement this feature as timeline monitor playback?
  • This is the main problem for the moment.
  • This could be transformed into a feature: if Kdenlive doesn't delete the preview files we can use it for an undo purpose. Then when a person needs no more the oldest previews file he could delete them by a command in the "Timeline" menu. Or we can decide that the timeline is shared in micro areas, of the length of the shorter rendering, so that if we have to render those areas again we'll overwrite the older rendering files because for each area can exists only one file with that name.

I guess that the rendering options are set on the easiest to playback DNxHD video format everything will be smoooooooooooooooth.

  • I changed color to green and will let you test for more feedback.
  • Of course, a button to stop the preview rendering should be done. My idea was to find some time to work on that new toolbar above the timeline and put a mini progress bar and stop button here.
  • The "Split view effect" was moved in the effect "Properties" window (top right corner), it was previously in monitor toolbar. It was not removed, but if you use it at the same time as the Preview render feature, it wont work. But this is fixable.
  • Rendering options are not yet editable, currently it renders to MP4 but I will add a setting like for the proxy clips to adjust it later.

I tested this feature with a complex timeline and it works great. I also had an idea for improvement:
This preview render should be video only, no audio. This way, when playing timeline, it plays the preview rendered video but the audio from original source clips. The big advantage here is that then, if we edit audio stuff in timeline (audio effects, add music, etc), this does not invalidate the preview render zone. In my typical workflow I often make final audio adjustments at the end of the project, so having this preview render giving a perfectly smooth playback while being able to edit audio would be really nice.
I made a few tests and this should not be too complicated to implement. In my tests, it was no problem to playback in realtime the rendered preview video with sound from original clips. Do you see any problem with this approach ?

I believe that this approach is the correct one.

Just a minor idea: what about later adding a "full preview render" button to the future toolbar? For easily rendering the complete project without having to set a full-length timeline zone first?

Finally, I have tested the "Timeline preview render" feature.
As usual, before to start with my notes, I have to make my compliment to you for the job.
For going forward from the messages we wrote yesterday I can add this:

  1. The mp4 codec has some issues when you playback backward. I guess that a smoother compression (even if it can occupy more space on disk - if you want to save space you can always use the proxy approach) could be a better choice. My suggestion is to use an MPEG2 High@High or a DNxHD MJPEG with bitrates between 25 and 35 Mbps if it's possible.
  2. For which concern the files length I guess that it's better to use very very short files. If we'll continue to use Mpeg formats (both Mpeg2 or Mpeg4) we could work with files long as the GOP length (Group Of Pictures - of the codec we'll choose to use. If we'll use an Mjpeg based codec we could use even shorter files (even just one frame long) but I guess this is too much. In my opinion, an interval between 12 to 30 frames could do the job. This could be useful for better fitting the length of the timeline zone we want to render and if we have to re-render modified zones.
  3. The option to choose in which folder or disk to put the render files is important. Then I believe that Kdenlive has to create a folder for each project named as the project itself. So if the timeline it is shared in small zones, long as the length of one render file, we'll find files named with the number of the starting and ending timeline timecode. So for each place, we can have one and one only render file. This could be useful for overwriting older render and for helping the application to locate the render files and load them when you open the project.
  4. I saw that not only the saved project isn't yet able to keep the render from the previous session but that you also loose the rendered preview if you disable/enable a clip you already rendered.
  5. For answering to Thediveo, I have to tell that other applications are able to indicate you which are the zones you have to render. The applications are able to know where they are not able to playback smoothly and they underline it to you, by a red line or similar indication, these areas. As Kdenlive is a Real Time Video Editor I guess we don't need it. Every PC has a different configuration so I guess that we have to let people choose which area they need/want to render. When you see that your computer is not able to smoothly playback a zone, you just can render it. So if you want to make "Full preview render" I guess you can export the project, as we done before, or set the timeline zone IN point at the beginning of the timeline and the OUT point at the end of it. Of course, this is just my opinion and a command in the menu which allows to do it, it's not a problem at all, on the contrary, it's something more.
  6. As a shortcut key for this feature, as I found that it was still free, I chose the standard one that all video editing applications use: the Enter key.

You probably know already that if I open a project and I want to render again a zone I rendered in a previous session, Kdenlive uploads immediately the existing rendering files.

Update on the yesterday night first impressions:

  • Regarding the point 1, I read again your previous post in which you told that in the future you'll want to allow people to select which codec to use for preview rendering: this is actually great, there are no other applications which allow you to do this. Of course, a default codec setting for each profile (HD, SD, etc), for helping user not skilled with video compressions, I guess it'll be important.
  • For the point 2, if it will be possible to choose the codec, everybody will be free to do what he wants. My suggestion about using very short clips remains.
  • On point 6, I just have to say that I made a mistake because the Enter key is already set for opening folders when you browse by the keyboard, and I think this is correct. I set F12 but probably we can use Shift+Enter for exporting and Ctrl+Enter for preview rendering.

Ctrl+Enter is already used (if I remember correctly) for opening the Render dialog, i.e. what you are calling "export".

massimostella added a comment.EditedMay 19 2016, 12:55 AM

I just tested the latest version you uploaded on the git.
Insert and overwrite feature works no more and I found a small issue in the disable/enable feature. I just opened 2 bug reports.

The rendering function is improving fast. I saved a rendered timeline and when I opened back the project everything worked very well. I'm sure you already know what I found during the daily test but I report you anyway just for focusing:

  1. if you add a filter, even if you disable/enable the effect, the rendering stay in place and you can't watch the clip without the filter. Same thing for the split view which doesn't work.
  2. If you change the parameter to the filter and then you come back to the rendered settings you lose the rendering. I guess that until when you don't overwrite the rendering files, you can come back to the situation you rendered. The render files have just to be loaded back. This can be useful for undoing purposes.
  3. If you disable/enable the clip you have no effects: Kdenlive continues to play the preview rendered files.

Then, I watched that now the preview rendering files are 25 frames long (I didn't test if it's a second based on the frame rate). During my rendering, it happened that the test timeline was for eg 3 seconds and 1 frame. Kdenlive rendered 24 black frames and my timeline end point was moved forward of near a second. Is it possible to share the timeline in 1 second length parts (and this is perfect) but to tell to Kdenlive to make shorter files (to cut them) when the rendering zone ends before the end of the 1 second length section?

Before to close, I want to thanks to Thediveo for the message.
For the moment I set F12 but when we'll fine tune the keyboard keys we'll decide what to do. Maybe Shift + Enter. We'll see.
What do you think could be better?

I was reflecting again on the Thediveo idea ( of a "full preview render" button into the future toolbar.
Probably when the "preview render" feature will be complete we could insert a button for enabling/disabling a continuous background rendering of the whole timeline. So while you are working just some of the CPU processing threads could render the job you already made. So, just some moments after you end your job, you can playback it smoothly. This could be useful mostly for 4K h265 productions.

thediveo added a comment.EditedMay 19 2016, 2:57 PM

I've tried preview rendering for the first time using recent git master: while I see the preview rendering progress bar running up to 100% I don't get any preview. After progress is finished, no green preview indication to be seen in the timeline ruler. Also, I don't see any temporary .mp4 files in ~/.cache/kdenlive in which I suppose they should show up. Also, no temporary .mlt file present.

Strange: on another project I get the proper preview rendering, so I also see the .mp4 files as well as the corresponding .mlt file. ???

Another issue I notice: my source footage are .mp4/H.264 clips. When preview rendering in 1s chunks, these chunks do not always correctly start with the desired frame. The result is a sometimes slightly rough playback with jumps in between -- not due to frame dropping but because rendering an individual 1s chunk does not correctly start where it is supposed to start. This may probably be caused by MLTs picky behavior when seeking in certain footage formats?

massimostella added a comment.EditedMay 20 2016, 4:36 PM

Sorry for the delay in the daily test.
Before to begin, I must admit that the multiple rendering zone selection is a new approach I never saw before that I like a lot. Great idea!
This together with the option to enable/disable a continuous background rendering of all the areas with effects could be the perfect and final approach for the preview rendering feature.
Now, my today report:

  1. Once you turn off an effect and then you turn it back on, you lose the rendering, same as if you disable and enable the clip. I guess that at least one undo step it's important.
  2. After you start the rendering action the progress bar waits that the first rendering file is created before to show up
  3. If I mute a track Kdenlive continues to playback the rendering files in the rendered zones
  4. I remind you that the option for selecting in which folder create rendering file is important
  5. I didn't find any compression profiles in the Timeline preview settings. Anyway, it was pretty easy to add some. I guess that for basic users it could be better to set default profiles for each kind of project (HD, SD, etc)

Here I add some additional notes though these are not related to the current feature:

  • Yesterday, when I opened the timeline ruler context menu, I asked to myself if it could be better to move the "Use timeline zone for insert" toggle there.
  • As there was for the K key I saw that when you press the J key for backward playback there is a delay.

I found a few premade preview render profiles. The only thing that I think needs improvement is to guess suitable profiles based on frame size and fps. When I opened the configuration dialog, I had a 24fps profile set or so, albeit default project is 25fps.

The preview rendering button looks very strange on Qt 5.5.1 when Kdenlive is rendering the preview. When the button is not selected, the e.t.a. and the progress bar is shown. But when clicking on the button, then it looks like this:

Automatic preview rendering is way too cool ... I now need sunglasses at work, even with Breeze dark theme :D

jessed added a subscriber: jessed.May 21 2016, 6:31 PM

Just created a Phabricator account, and I need to say that this feature is way, WAY too cool. Thanks so much to JB and the team for implementing this. I'm testing it currently with a few projects and will offer any helpful feedback I can.

Great work guys!

Thanks Jesse,

I am quite happy about how this feature has evolved now. Still missing :

  • configure option to decide where the rendered files are saved. (boring but easy. By the way I always wanted to change the current behavior that saves thumbnails in $HOME/kdenlive to a more standard default location, like .cache/kdenlive).
  • A few cases don't invalidate rendering: hide a track, and maybe a few other less common actions (should be easy)
  • Undo: I just implemented a one level undo, meaning that if you make a mistake and directly undo it you can recover preview files. I don't think I will expand the feature much more.
  • Currently there is a problem if you change your project (and timeline previews with it ) but don't save it. The preview files stay at the last status of timeline, so when reloading your project, previews will be all wrong, reflecting the unsaved project. Not sure how to handle this
  • I guess we should add an option to quickly show/hide the timeline preview so users can make sure everything is ok.

What about storing the project file timestamp or some hash of it in a simple cache ident file in the .cache/kdenlive folder? That is, a simple small file that accompanies the mlt file and the other rendered preview chunk files.

Great job! As usual! :)
After I read your next steps, I just can say that soon this feature will be complete and very well implemented.
Just a couple of notes:

  1. Remember for the actions which don't invalidate the rendering also to manage situations when you have to enable/disable effects and enable/disable clip on the timeline.
  2. I was thinking about the automatic rendering feature: in all major programs, the red line appears automatically where there are not just plain video clips but also effects, filters, transitions, etc. which are not working in real-time GPU accelerated mode as the Movit ones. This could be useful so if you turn on the automatic preview, you have not to set manually the areas you want to render.

For ending, I add a couple of questions though they are not related to the current feature:

  • After I update to Qt 5.6 Kdenlive playback is no more smooth as was before. Is it possible? Is there some connection between these 2 things?
  • Even if I have the KDE Plasma Desktop installed in my Ubuntu I have issues with some icons. What can I do for fixing them?

Thanks in advance to everybody can help me about.

  1. Remember for the actions which don't invalidate the rendering also to manage situations when you have to enable/disable effects and enable/disable clip on the timeline.

I think all actions are now handled correctly. If you still find issues, please report them.

  1. I was thinking about the automatic rendering feature: in all major programs, the red line appears automatically where there are not just plain video clips but also effects, filters, transitions, etc. which are not working in real-time GPU accelerated mode as the Movit ones. This could be useful so if you turn on the automatic preview, you have not to set manually the areas you want to render.

Yes, but it's not that easy. Some effects can easily be handled while some don't... I also thought to check the playback framerate to automatically mark zones as "to be previewed". However I think for the moment we can live with the manual option.

  • After I update to Qt 5.6 Kdenlive playback is no more smooth as was before. Is it possible? Is there some connection between these 2 things?

No idea... several people reported major slowdown with transitions (not related to Qt 5.6) recently but I personally have not seen a real problem, I will try to spend some time later next month on performance.

  • Even if I have the KDE Plasma Desktop installed in my Ubuntu I have issues with some icons.

Did you install Kdenlive ? Currently when new icons are added, Kdenlive needs to be installed in a standard path so that icons are found.

I plan to make major changes to the icon management (T1239) but it all relies on KDE Frameworks 5.23 that has not even been released so it will probably take one year before it reaches distributions :(

In case you are installing Kdenlive in a non-standard location, please see on how to set up the required environment variables, so that Kdenlive correctly finds its icons and configuration data. I'm using such a setup myself so I know that it works.

I just created a new task for preview file location : T2582

I finally made all the tests.
These are my suggestions by keeping the same number we used for our latest communications.

    • When you completed a rendering if you make one step undo the rendering stays in place and when you move back forward the preview render is lost. (eg. you insert a clip in the timeline and you call a preview render for it. You call for one undo step and the clip is no more in the timeline but the rendered zone is still marked green and you can playback it. You call for redo and the clip comes back on the timeline but you lose the rendering.)
    • You place a clip on the timeline, you add a filter on it and you render it for previewing. Then you turn off the filter by clicking on the eye icon but if you turn on the filter by clicking the eye icon again, you loose the rendered preview. No way to recover it also by calling for undo.
    • You place a clip on the timeline and you render it for previewing. Then you mute the video track where the clip is and you loose the rendering. But when you turn the track on again the rendering is not restored.
    • If the timeline ends at 12 mins 03 secs and 01 frame and you call for preview rendering your project will be 24 frames longer with a black tail.
  1. I absolutely agree.
  1. OK
  1. Actually, I had to admit that I launched the program from the build folder. After I installed it the icons show up perfectly except for the ones overlayed on the monitors. The only way to have the correct icons is to run the Plasma-desktop. In Ubuntu-desktop (I have different installations of it) or I have no icons or the wrong ones.

One final short note about a "strange" timeline behavior (I'll post other notes on the right Phabricator tasks):
Each time you begin a project from scratch when you insert the first clip the In point of the timeline zone bar moves at frame 10 instead of stay on frame 0.

Just had a chance to test the timeline preview feature. A few thoughts and issues:

  1. The "Unset Preview Zone" and the "Add Preview Zone" icons are both the same. Suggest changing the unset one.
  1. When I load Kdenlie, the Timeline Preview button doesn't appear. I have to remove and re-add it in the toolbar configuration window. It shows up then, but when I restart Kdenlive, the button vanishes again.
  1. In the current git master build I'm testing (date May 22, 2016) the Timeline Preview isn't working at all. The Timeline Preview button icon vanishes when I try to start it, leaving only a progress bar that doesn't proceed. The timeline shows the preview zone I created, but it stays red. No indication of activity. My CPU doesn't show that there's any activity on Kdenlive's end, either.
mardelle added a comment.EditedMay 23 2016, 12:06 AM

Ok, I finally found a way to implement a correct undo/redo for timeline preview I think. Preview files are now stored in a folder specific to each project (more on that later).
I fixed some bugs described in Massimo's comment point 1. We now delete preview files older than 5 undo steps, that should be enough to recover a problem and keeping larger history might result in huge cache.

Hiding a track does not work yet with this feature because it is not integrated in the undo/redo system. Should be easy to fix though.

About icons, any contribution is welcome.

Re: icons ... give me some time. I have an idea now about the preview zone add and remove buttons.

Jean-Baptiste, I've sent you a bunch of new and updated icons for preview rendering and advanced editing functions. Hope you can make use of it.

New tests update:

  1. I thought about some behaviour I saw in the timeline and maybe I have to admit that my suggestion to use the timeline timecode as reference it looked like as an easy approach but maybe it was not correct. Today I put just a clip in an empty timeline and I rendered it. Then I dragged the rendered clip around on the timeline and, of course, it lost its preview render as it's supposed to be. Then I reflect on what I expected in such a situation if I was into Premiere or FCP: the preview rendering follows the clip. This means that those developers used a different approach, a clip based approach. Do you think is it better, more convenient and easier to implement? Maybe is for this reason that it's not possible to turn on/off a filter, enable/disable a clip and mute/unmute a track and to have back the preview rendering.
  2. The undo works better than before but it's not still to clear how it reacts. Probably the render has to be one of the action of the undo list but as it's a background performance, I know that it's a no-sense. 5 undos are absolutely more than enough.
  3. I made some experiment with codecs and compressions. I notice that when you chose a different codec in the "Manage Encoding Profiles" window you have no way to save your choise and that Kdenlive continues always to use the default profile though you changed it.
  4. I made a mistake by entering a parameter in a new profile in the transcode window. When I transcoded a clip on the bottom of the project window an alert bar shows up asking me to read an error log. After I read the log about the error, I was not able to close the alert bar.

By the way, the compression parameter I inserted is an Intermediate MJPEG codec who works very well and it's lighter than the DNxHD. If you want to test it's an AVI capsule and the code is this:
-s 1920x1080 -r 25 -vcodec mjpeg -qscale 1 -acodec pcm_s16le

  1. The current timeline preview works by adding a track on top of your current timeline and puts rendered chunks on it so that they cover your actual timeline. Using a per clip approach like you describe would be completely different, more like the way the proxy feature works. Of course, the clip based approach has the advantage of not being lost after you move a clip. But it would not solve the transitions issue. If you have several complex transitions, only having the clips pre-prendered would not guarantee a smooth playback. Implementing it would require at least as much work as the current approach. Switching an effect on/off, en/disabling a clip should work now if you use undo. Hiding a track should be available soon as well.
  1. I made a few improvements in the last hours, and yes, it is based on the undo stack. Let me know if you encounter unexpected behaviors
  1. In the Project Settings, there is a combobox allowing you to select a profile, not much tested though.

About the codec, we can probably fine tune the settings.

Fast answer to point 3:
I found the combox. I was trying to select the profile through the Kdenlive settings>timeline>Timeline preview profiles panel.

The preview profile I sent you is not working correctly: it creates intermitting chunks; 1 second "green" and 1 second "red". Actually it's not the first time I saw this "strange" behaviour. It happened yesterday too with the current default profile. I was rendering an action camera mp4 format.

massimostella added a comment.EditedMay 27 2016, 12:57 AM

Hi, I reflected on the preview rendering feature:
The timeline based approach is ok. It involves a precise mind set for exploiting it but it's good enough.
Once you learn to think in an "undo" vision, you don't loose too frequently your rendered preview.
I don't know if you want to fine tune the feature as it is now and move forward or if you want to implement it more.
For this second situation I have 1 proposals.
What do you think about a "consolidate" feature? Is it too hard to make Kdenlive able to keep rendered previews inside virtual clips in the Library? Once in the timethine they are immediately "green".
One stupid question, it's very secondary: is it time consuming implement that the latest rendered chunk is shorter than the standard 1 second lenght?
Every feedbacks is accepted. :)

Everytime I try the preview rendering, it says in the status bar: "Preview rendering failed, check your parameters". Is this feature currently working?

Also, is it currently set up that you have to add a preview zone, THEN click preview render? Or will it simply preview render the in-out zone points if you click it?

Jesse, it should be working, at least it did so for me on a project I just finished this day using recent git master (well, call me gambler doing projects on git master). However, from time to time I'm also seeing this error message. I'm unclear as to how to trigger it.

In T1949#39457, @jessed wrote:

Also, is it currently set up that you have to add a preview zone, THEN click preview render? Or will it simply preview render the in-out zone points if you click it?

First one: first add zone(s), then start preview rendering. This way, you can even render multiple, non-continuous zones.

Thanks for the info, thediveo. Looks like I'm getting this from Terminal when I try preview render:

""Preview rendering failed, check your parameters"

WARNING: bool Phonon::FactoryPrivate::createBackend() phonon backend plugin could not be loaded WARNING: Phonon::createPath: Cannot connect Phonon::MediaObject ( no objectName ) to Phonon::AudioOutput ( no objectName ). WARNING: bool Phonon::FactoryPrivate::createBackend() phonon backend plugin could not be loaded WARNING: bool Phonon::FactoryPrivate::createBackend() phonon backend plugin could not be loaded"

What's Phonon? Could it be contributing to this issue?

In a project I just finished today I noticed something odd that seems to be related to preview rendering; however I'm not exactly sure, another reason could be the recent timeline code refactoring.

Alas, as I worked on my project at one time I had some parts moved to later timeline positions in order to make room. As I finalized the timeline, these later parts ended up in earlier positions. Thus, the overall total length decreased. However, when rendering, the full project rendered is actually thirty seconds longer than the final clip in the timeline. When scrubbing there is some content getting shown in the project monitor albeit there are no clips in that part of the timeline.

I suspect that the content may come from an older preview rendering. Disabling preview rendering, manually cleaning the cache, and reloading didn't cure the problem however. So I may be actually wrong as far as the content is concerned. But maybe the invisible preview producer may still cause such weird effects...?

Jesse, Phonon is related to audio, but not video. I doubt that it is related to preview; but then, I may be wrong here.

Just did some more testing. Looks like my project and preview settings are 1080p at 24fps. Setting it to 25fps makes everything work fine. So, possibly and issue with the 24fps framerate?

Details are in a bug I submitted a week ago (

I have to admit that I'm stuck with 25 fps for all the time so far :)

I've been using this feature for various projects with the latter git-master builds, and it's honestly working REALLY well! The only encouragement I'd make is to have the preview bar not overlap the boundaries set by the in-out zone slider above the timeline. If it rendered specifically where it said, that would be killer.

But seriously, great job, JB. This feature is a HUGE leap in workflow improvement for Kdenlive.

A few thoughts after some more testing:

(1) Any chance we can get an option in the sub-menu of the Preview Render button that says something like "Clear preview zones" which would remove all preview zones, regardless of whether the zone slider is over them?

(2) I often find myself instinctively clicking the Preview Render button while it's rendering to cancel a preview render, and forget that I have to go into the menu to stop the preview render. Is there any way we could have it so clicking on the Preview Render button while rendering would cancel the render?

massimostella updated the task description. (Show Details)Sep 1 2016, 1:35 AM
jessed added a comment.Sep 9 2016, 7:35 PM

Updates are very solid, great work, guys!

One thought while using the latest git master build: before any initial preview rendering is done the first time, there's no preview render bar in the timeline. Even after the user adds a preview zone, the bar doesn't appear showing the zone you added for preview render. Only after you start a preview render does it appear, and consequently re-sizes the timeline a little bit.

Would it make more sense to have the preview zone bar present the entire time, even from Kdenlive start?

Timeline preview rendering has proved to be rock solid. The only UI-wise issue I have is that the red used for invalid chunks is barely visible on my desktop where I use a dark color theme.

mardelle closed this task as Resolved.Aug 9 2018, 7:13 AM