How to watch videos in Chromium?

Question

I can't see videos in Chromium in Ubuntu 16.04. How can I fix that?

http://www.quizover.com/oer/course/adaptive-submodularity-a-new-approach-to-by-daniel-videolectures

jalal@klein:~$ dpkg-query -s adobe-flashplugin
dpkg-query: package 'adobe-flashplugin' is not installed and no information is available
Use dpkg --info (= dpkg-deb --info) to examine archive files,
and dpkg --contents (= dpkg-deb --contents) to list their contents.
jalal@klein:~$ sudo apt-get install  adobe-flashplugin
[sudo] password for jalal: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package adobe-flashplugin is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'adobe-flashplugin' has no installation candidate

I installed this: sudo apt-get install browser-plugin-freshplayer-pepperflash YouTube videos play with no sound. Please suggest fixes.

UPDATE: I added these, updated and installed flash but I can't hear video voices still:

$ sudo vi /etc/apt/sources.list

     48 deb http://archive.canonical.com/ubuntu xenial partner
     49 deb-src http://archive.canonical.com/ubuntu xenial partner

$ sudo apt-get update
$ sudo apt-get install adobe-flashplugin