Chromecast allows you to stream MP4 video files on HDTV, but unsupport with other video files like MKV, VOB, FLV and AVI. If you would like to cast any local videos from your PC to HDTV using Google Chromecast, you should try with an application like DreamStream.
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More you can do with DreamStream:
> Watch Web Videos on the Big Screen via Chromecast
> Stream camcorder videos from PC directly to your TV