[kdenlive] Black video when rendering with v0.9.10

[Narcis Garcia]

I'm using Kdenlive 0.9.10 in Ubuntu 14.04 and, since few months ago, any
rendering productes a file with video track in solid black color. Audio
is good.
Tested with MPEG-2, MP4 and webm as target formats, and OGG and MP4 as
source clip formats. Tested with no edition (only putting 1 clip in
timeline and render to file).

What do I need to look to find the problem origin?
Thanks.