After upgrading to Ubuntu 14.04 64bit I noticed that Steam was misbehaving and some features were unavailable. The first video of any game on the store was appearing as a single picture and couldn't be played and any other video wouldn't play normally on full screen.
- The first video of any game from the store in Steam under Ubuntu 14.04 64bit is not playable. This is also mentioned by other members of the community.
First Video in Steam is Not Playable "0:00/NaN/NaN"
- (Possibly) Full screen videos in Steam have a glitch where the top part of the screen is flashing and doesn't display video. Also the sides of the screen might develop the same glitch.
Flash layer is the issue and causes all the problems. The solution is to download a 32bit version of libflashplayer.so and add it to a local Steam directory.  Do as the following,
- Close Steam
- In your browser go to http://get.adobe.com/flashplayer/otherversions/
- Download a tar.gz of the 32bit flash player for Linux.
32 bit Flash player in tar.gz
- tar xzvf install_flash_player_11_linux.i386.tar.gz
- mkdir ~/.local/share/Steam/ubuntu12_32/plugins/
- cp libflashplayer.so ~/.local/share/Steam/ubuntu12_32/plugins/libflashplayer.so
- Start Steam
The first videos should be playable now and the screen glitch should also be gone. Worked as a charm for me.
By default the Steam directory is ~/.local/share/Steam however if you have changed this, please change it in the above commands.
You can remove the extra "junk" files that were unpacked from the tar.gz file. Untaring creates a "usr" directory in the download location that can be removed with rm -rf usr and the readme.txt with rm readme.txt.
 - http://www.reddit.com/r/Steam/comments/2lrbp3/steam_linux_first_video_in_store_page_never/
 - http://wiki.gentoo.org/wiki/Steam#Flashplayer_on_amd64