Bug with "selected zone" render that only affects non-official builds

Vincent Pinon vpinon at kde.org
Mon Oct 14 20:23:16 BST 2019

Le lundi 14 octobre 2019, 19:42:18 CEST Alistair Riddoch a écrit :

I have come across a bug which affects rendering a selected zone, but does not occur when using the Appimages downloaded from kdenlive.org. I am uncertain whether to file a bug in the tracker, as I'm guessing it is actually a problem with a dependency. I'll describe it here, and I'm happy to file it properly, and help resolve if that seems appropriate.

I'm using Fedora 30 and the bug is present in all the binaries I have built from source since some time during 19.04. I have built from the release labels, from the 19.08 branch, and from head and seen the same problem in each case. The bug is also present in the semi-official rpm package from RPM Fusion. The installed Melt is mlt-6.16.0, and is comon to all recent affected builds.

The bug is that when I render a "selected zone" of the project, the output of the render is not the correct length, and doesn't contain the correct range of the project output. Very frequently the output is only 1 or 2 frames long, and renders almost instantly, despite the selected zone being much longer.

Repro steps:
Create or load a project with some clips on the timeline.
Define in in-point on the project time line which is _not_ at time 00:00:00.
Define an out-point on the project time line which is after the in-point.
Open the Render dialog.
Select "selected zone".
Format does not appear to matter, but I have only tested with WAV and MP4.
Press "Render to File".
Expected Result: The output video is the range of the project selected.
Actual Result: The output video is apparently random in length, and not obviously directly related to the selected zone.

I attach a project file which is a trivial repro case for the bug, and the mp4 file I got when I tried to render a 2 second zone from the middle of this project. The actual output is 2 frames long, and is not correct for the start of the selected zone.

Please let me know if more information is required, or if I can do anything else to help fix the bug.

Keep up the good work!


Alistair Riddoch
alriddoch at googlemail.com

Hi Alistair,

Try to build MLT from git, I believe it has commits fixing this bug (in June, seen on 19.04 releases, using the new consumer xml tag) :
690d3ed55f98d8e31affb1b5dbc84c6948248099 - Pass the consumer's in/out properties when using movit or multi consumer
434dbcf62048cc1220c425c2adc77697b4d40ffb - Fix multi consumer doesn't correctly handle in point


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