I had this happen a few days ago. I then reset my Chromecast back to Factory Setting and re-installed it. The problem went away.

Buy the Premium version. That activates the Playlist function.

You can buy a device (eg. Blackrock HDMI converter) that will take HDMI input and pass the video and audio signals to the HDMI output. But it also "taps" the audio and makes it available separately to stereo RCA plugs.
You can then connect those to an amp, speaker bar etc.

So, you could plug the Chromecast into the input of that device and use an HDMI cable to connect the hdmi output to the TV. Connect the audio output cables to your Amp.

Just turn the TV volume down when you are casting.

VOB files will play!

Whenever I accidentally tried to open Videostream twice I got a message saying something like "You love us too much." It wasn't possible to run a second copy simultaneously on one PC.

It's not a different program. When I bought Premium, the Playlist option was no longer grayed out. It then functioned.

I have used Videostream to play VOB files. To play them in order, I would use Playlist and just set them up in order.

For the past week (last week in January 2016) the team does not appear to be available for any communications. Very strange. Usually they are super fast in responding.

Have similar problem. I bought Premium Lifetime using a Google account but later deleted that account and opened a new one. Now Playlist won't work, probably because my Premium licence remains tied to the old one.
Have tried for 6 days to get the Team to respond but, unusually, the only response received is that automated one that says they are very busy. I'm guessing that only they can make the account switch.

Further update.
It's been a few days now since I reset Chromecast and reported that the problem went away.
I have watched several MKV videos since then and have not had a single instance of VS suddenly quitting. Everything is great!

Me too. No buffering, no hiccups, smooth playback but, suddenly, VS stops and I'm back to the VS welcome screen. I have to restart the video and restart playing from the point where it was playing when it was cut off. When it does happen it's about half way thru a movie.
Most of the videos this happens with are MKV's downloaded from MOVREEL.
My PC is fast (I7, 12MB RAM, SSD) and connected to the router via Ethernet cable.
My Internet speed is rated at 55mbps.

Update: As suggested, I reset Chromecast. After that we had 4 hours of videos (3 separate files) without a single hiccup, Looks good!