movie_cutscene stops working

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I start my game with a short cut_scene and if I create a new renpy project and paste in this code it works fine:

label start:
$ version = 0.0

call initialisation

scene lobby2
show SophieSmile114

window hide
$ renpy.movie_cutscene("01/SophieSmile.webm")
pause
window auto

Then after some time (could be days/hours/weeks) something happens, and I cannot find out what, and I no longer see the movie.

I create a new project, drop all my files in and it all works fine again for a while, then stops again.

I have tried deleting everything in the game/save and appdata directories and but that doesn't help.

Does anybody have any idea what is going wrong or how I could try and isolate the issue.

[vollschauer]

What version of Ren'Py do you use? In some "old" version there was a bug in renpy.movie_cutscene not showing the movie ...

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6.99.14.2.3333

[vollschauer]

You need to update!

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If you turn off the sound in options.rpy then movies stop working!