Audio not playing through Vizio sound bar when streaming?

I have a samsung 7000 led smart tv. I have a vizio sound bar connected via optical cable to the tv. In the settings menu of the tv the internal speakers are switched to off and external to on. This works 100% for my audio and all audio comes out of the sound bar. However, when I stream a movie, on some movies the audio doesn't play at all through the sound bar. However, at first I thought it was the video file but when I go back to the settings menu on the tv and switch it to external speakers off and internal on I am able to get audio and hear it just fine. Wondering what this could be, any suggestion guys?

Thanks

[Cerberus]

vizio soundbar doesnt support the audio codec used or tv doesnt support external audio for certain audio codecs.

please provide following information on files that dont work.

viewtopic.php?f=5&t=19 & http://wiki.serviio.org/doku.php?id=mediainfo