cubicweb-mediaplayer #3654054 Optimaize SoundFile encoding [validation pending]

Avoid to much unclosed TemporaryFiles

prioritynormal
typebug
done in0.1.2
load0.200
load left0.000
closed by#3adf36cb06f7 [sound] optimize SoundFile rencoding : use Popen communucate (closes #3654054)