chromecast: only create the sub-sout when we know the ES in use
chromecast: only create the sub-sout when we know the ES in use

we then decide whether we want to remux or transcode
use the Matroska container as it allows better streaming and more codec than
the Chromecast supports (VP8 / Vorbis)

Signed-off-by: Thomas Guillem <5f50a84c1fa3bcff146405017f36aec1a10a9e38@gllm.fr>

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc