crash in libmlt after adding sound effect

[Sławomir Nizio]

Sabayon
tested and happens on: Openshot 1.2.2, 1.3.0, 1.3.1
with mlt 0.5.10 and 0.7.2
with ffmpeg 0.6 + patches
Python 2.7

from dmesg for melt 0.7.2:
openshot[16206]: segfault at 4 ip b555174c sp bfdb1eb0 error 4 in libmlt.so.0.7.2[b5543000+21000]

steps to reproduce:
- import file (tested with swf and mp3)
- drag and drop file to the track
- from Effects add any audio effect (tested with echo and bass)
- click on the time scale as if you wanted to move the "time pointer"

what happens: immediate crash.

(Mlt module imports in Python without problems.)

[Andy Finch (fincha)]

Can you check you have the sox package installed?

[Sławomir Nizio (snizio)]

Yes. Happens with sox 14.3.1, 14.3.2 and no sox.

[Sławomir Nizio (snizio)]

Hello again.
(I don't think it's a duplicate of bug #769743. )
Tested with OpenShot 1.4.0, same.
I've generated a backtrace and it looks like bug #546498 - any idea?
Attaching backtrace.

x86, sox 14.3.2, mlt 0.7.2, Python 2.7

[Olivier Girard (eolinwen)]

Hi,
Update your version of MLT she had a nasty bug and re-try with the 0.7.4.3 Are you on Ubuntu ?

[Sławomir Nizio (snizio)]

Thanks for the reply!
I use Sabayon (and more: I am going to make version bump of OpenShot soon there).
I've made a quick dirty upgrade to mlt 0.7.4 and the crash doesn't occur anymore. The number of Audio effects has dropped to only one (Balance), though (would need to take a look).
Another solution would be to find which commit in mlt fixes this issue and patch 0.7.2 to keep the Gentoo version. If you have a suggestion which commit(s) fix this issue, please let me know. :)

[Sławomir Nizio (snizio)]

I'll post my observations, maybe they'll be helpful for you or other users. Maybe these facts are known to you OpenShot developers, so you'll get a confirmation.

The crash doesn't occur with MLT 0.7.4, and the exact "fix" in MLT that does it is the commit that… updates version number in MLT to 0.7.4 (on top on previous commits, certainly). And as you know, if OpenShot 1.4.0 detects MLT 0.7.4, it does some checks if an effect is available:

> Warning: effect not found in your version of Sox: sox:echo

etc., etc. and doesn't display non-existent effects.
So, with MLT 0.7.4 I got only "Balance" effect in audio effects.
And it turned out that with MLT 0.7.2 the crash I'd described *doesn't* occur if I use the Balance audio effect.

So in a few words: it looks like the crash has been caused by OpenShot (or user) trying to use a sox effect that doesn't exist (but was listed anyway). It's not listed with MLT 0.7.4 and the crash doesn't happen, because a user can't use it.

Ref.: openshot/windows/TreeEffects.py (for 1.4.0), populate_tree. Good to see it fixed!