It's a bug in Audience and it's already reported on Launchpad: https://bugs.launchpad.net/audience/+bug/1362910
P.S. If you've wandered to this post and saw this bug, and it affects you - please click "this bug affects me" on a launchpad to let developers know about the IPU
I think you are right. There is no button or command on the gui to delete the played videos.
But you can delete the last played videos over the terminal with following command.
gsettings set org.pantheon.audience last-played-videos 
Due to US patent law, elementary is not able to freely distribute codecs for many popular media formats. You will likely need to purchase a license for the codecs from Fluendo on their website.
However, if you're in a country where you are not affected by this patent law, you can install a set of codecs provided by Canonical with the following command in ...
vlc allows you to cycle between different aspect ratios using the a key or the menu Video->Aspect Ratio
mpv allows to cycle between different aspect ratios with a key set in ~/.mpv/input.conf. To use the A key, you need to have the line A cycle-values video-aspect "16:9" "4:3" "2.35:1" "-1". The file (and folder) can (and may need to) be created manually ...
Since Ubuntu 15.10, libdvdcss (the package required for CSS decryption) is installed as part of the libdvd-pkg package, with no additional steps required.
sudo apt install libdvd-pkg
The default Videos app in elementary OS is quite buggy, and while the Play Disc option appears after installing CSS support, playback fails. A workaround is simply to install ...
Actually this is a feature, not a bug.
However if you do not need it, you might want to implement some sort of solution to reset it. Some alternatives depending on your exact needs follow.
You might want to start Audience from a wrapper script that resets
the org.pantheon.audience.current-video value just after quitting:
Okay, at the risk of being considered rude, I need to ask why coderMess decided to not answer the user's question, but instead offer up advice on using another piece of software.
Sure, you can use VLC, but what if you don't want to?
And why bother answering a question with the advice of using different software?
If we want this whole thing to work, we ...