It is not recommended to install random packages with dpkg.
Read the whole answer before taking any action
Apt is having an issue because it has not associated with your install of
ffmpeg. As far as it is concerned you do not have
ffmpeg installed and is giving you the above error because of this. Your output of
apt-cache policy ffmpeg proves this. I am not aware of methods to associate a random
.deb file with
apt unless your package sets up
apt during its install process. If someone can correct me about this, I would greatly appreciated it. If you need a package that is not available in you current repositories, you can, at your own discretion, add testing/unstable/backports/whatever repository to your sources.list that has the package you are looking for and use the package manager.
I do not recommend you use an unofficial Debian repo.
Look up the available versions of
ffmpeg here. If the version you want is in a repo other than stable you should then add it to your sources.list. If you set up "Apt Pinning" you can manage multiple releases of Debian with little overhead. To fix your installation of
ffmpeg start by removing your current instance so we can start from scratch.
apt-get purge ffmpeg
dpkg --purge ffmpeg
dpkg -l | ffmpeg
ffmpeg and then looks to see if it is installed. You should be looking for an
rc status as per this post. You can then follow the guide in the wiki about apt pinning to add testing and unstable repos. Do not forget to create the files in
/etc/apt/sources.list.d/ for each repo you plan on using, and a corresponding
/etc/apt/preferences.d/ file. Once you have created the proper files to get set up with apt pinning you can then simply run:
apt-get install ffmpeg/unstable
ffmpeg from the unstable repo. You can substitute unstable with whatever repo your desired package is from if you set up apt pinning.
However if you absolutely must use an unofficial Debian repo
Here is a guide to add a third-party repo that contains the
ffmpeg package you a probably looking for. If you decide to go with apt pinning you will need to create the repo (
/etc/apt/sources.list.d/deb-multimedia.list) and preferences (
/etc/apt/preferences.d/deb-multimedia.preferences) instead. Complete the following steps after purging
ffmpeg in the manner described previously.
Add this line:
deb http://www.deb-multimedia.org stretch main non-free
Save and exit. Now follow these steps:
The “-oAcquire::AllowInsecureRepositories=true” option is mandatory since Buster and thus also needed for unstable.
apt-get install deb-multimedia-keyring
Since Squeeze you can install this package with apt-get. Simply press y when the package ask what to do (don't press return).
If apt-get can not find the new key, do that :
sudo dpkg -i deb-multimedia-keyring_2016.8.1_all.deb
You can verify the package integrity with:
Final and mandatory step.
apt-get update and
apt-get dist-upgrade to install all packages related to ffmpeg.
After that you can run
apt-get install ffmpeg and you should have the correct package.
I understand this covers a lot but I wanted to be comprehensive. My personal philosophy with administrating Debian is to not stray from stable if possible, not stray from official repos with properly set up apt pinning according to the Debian wiki, and to carefully limiting and managing anything from a
.deb or installed from source. If you can help prevent there from being conflicts between versioning of packages/libraries by having everything you possibly can be managed by
apt you should be safe.
Sorry if this is too long winded or not what you needed I just wanted to make sure I covered all the bases. Best of Luck!