Bug 374502

Summary:	Problem with transparent output rendering
Product:	[Applications] kdenlive	Reporter:	Fred Périé <f.fredperie>
Component:	Rendering & Export	Assignee:	Jean-Baptiste Mardelle <jb>
Status:	RESOLVED FIXED
Severity:	normal	CC:	fritzibaby, wegwerf-1-2-3
Priority:	NOR	Flags:	fritzibaby: timeline_corruption+
Version First Reported In:	16.12.0
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:	20.08.0
Sentry Crash Report:
Attachments:	transparent image compositing menu

Description Fred Périé 2017-01-03 16:35:58 UTC

Created attachment 103168 [details]
transparent image

I was previously using kdenlive 15.12.3 in Mint 18 (the standard depot version) and was able to successfully export transparent tracks using codec ffv1 and pix_fmt=bgra (I am doing live compositing with the resulting files…) Note Display is correct

with current version 17.03.70 with melt 6.5.0 both compiled following the guidelines https://community.kde.org/Kdenlive/Development/KF5 the ouput files are not transparent altough the pix_fmt looks correct

To see the bug, use a fully transparent png (alpha=0 in the entire 1920x1080 image) import it in the timeline and then export using the following parametres for the rendering profile
f=matroska acodec=pcm_s16le ac=2 vcodec=ffv1 aspect=%dar pix_fmt=bgra

the ouput mkv is not anymore tranparent. 

This "bug" is also there in 16.12.0

Comment 1 Jean-Baptiste Mardelle 2017-01-03 18:02:22 UTC

Created attachment 103170 [details]
compositing menu

Kdenlive adds automatic compositing transitions between tracks. To disable it, you must set the "Track Compositing" to "None", it is in the drop down box on the left side just above timeline, see attached screenshot. With this option, transparent rendering should work (it did in my test). Please report back.

Comment 2 Fred Périé 2017-01-03 21:07:03 UTC

Thanks Jean-Baptiste, it is doing what I expected.

Maybe a word of explanation on  https://kdenlive.org/project/timeline-track-compositing would be welcome.

Comment 3 Wegwerf 2017-03-17 17:19:08 UTC

Frédéric, what would you suggest to improve the blog post of ours you're referencing? Just give me some clue, and I will update the post, and possibly write a dedicated post on it.

Comment 4 Wegwerf 2017-03-17 17:21:04 UTC

So, the usecase of yours is exporting *single*(?) tracks with transparency to transparent video? Do I get this correct?

What about multiple tracks? Not your usecase, or is it?

Comment 5 Fred Périé 2017-04-10 15:24:09 UTC

(In reply to Wegwerf from comment #4)
> So, the usecase of yours is exporting *single*(?) tracks with transparency
> to transparent video? Do I get this correct?
> 
> What about multiple tracks? Not your usecase, or is it?
Thanks for you question.
Sorry for my late answer. Yes I use multitracks with transparency and the bottom tracks has also transparency; I export the edited timeline using the ffv1 codec and pix_fmt bgra. This solution allows a transparency channel in the exported file and it is consistent with what was in the timeline. Those file are then treated in my own program for live compositing. It works fine.
Fred

Comment 6 Fred Périé 2017-04-10 15:26:18 UTC

(In reply to Wegwerf from comment #3)
> Frédéric, what would you suggest to improve the blog post of ours you're
> referencing? Just give me some clue, and I will update the post, and
> possibly write a dedicated post on it.

Hi I would love to. As a matter of fact, I didn't understand anything in the blog post you suggested. It was much clearer in your answer in this thread. This might be the clue you want, no?

Comment 7 emohr 2020-12-24 16:24:46 UTC

You can now export videos containing alpha channels (transparent). Goto Render -> choose "Video with alpha". Try with version 20.12.0.