Fix: A required codec could not be found with Plex

When Plex Media Server determines that a media file requested by a client cannot be direct played by the client, Plex will attempt to transcode the file before sending it to the client. Plex will use a codec that is installed on the server to transcode the file.

If the codec does not exist on the server, then Plex won't transcode the file, and will display and record the following error:

Conversion failed. A required codec could not be found or failed to install.

The error indicates that Plex couldn't find the codec required to transcode the file on the server, but doesn't tell you how to fix the problem.

This article will provide a few methods you can use to fix this error.

Fix: A required codec could not be found with Plex

How are codecs installed by Plex?

When you install Plex for the first time, the codecs it needs to transcode media files are not installed by default. Only after you log into Plex, or begin to transcode media files will Plex install the necessary codecs. These codecs are used by Plex to generate the optimized versions of the media files.

You can see the codecs that are currently installed on your Plex server in the Plex data directory in a "Codecs" subdirectory.

If you were to navigate into that directory you will see a few directories, and in one of those subdirectories you will see all the codecs that are installed - both decoders and encoders. If a required codec is not installed, Plex will go and download the codec from their server. When a codec is installed, it is persistent, so it won't be removed.

You will also find that when Plex updates, you may notice that the codecs are also updated, if needed.

The error "Conversion failed. A required codec could not be found or failed to install." is caused by Plex not having the required codec installed in the codecs directory. As I mentioned, Plex needs to download and install the codecs before it can transcode a file.

There are a few reasons why the codecs could not be installed, so let's look at a three fixes you can try.

1. Check the Internet connection

The first fix is simply verify that your Plex server can access the Internet. More specifically, it will need to access the following domains:

Plex Codec Required Domains
DomainDescription
plex.tvA request is sent to this domain to get information about the codec to download.
downloads.plex.tvAfter getting information about the codec to download, the codec is downloaded from this domain.

If the Plex server cannot connect to any of the two domains listed above, then Plex won't be able to download the required codec.

2. Check directory permissions

Another reason a codec cannot be installed by Plex could be due to a permission issue on the codec directory. Since Plex will need to download the codecs from the Internet, and then install them into the directory, the user running Plex will need read/write permissions on the codec directory.

You should verify that the Plex user has enough permissions on the directory to install the codec.

3. Delete the codecs directory

If the above two fixes don't resolve the issue, one thing you can try is to delete the codec directory entirely, and then have Plex recreate the directory and download and install the codecs again.

This is the last ditch effort to fix the issue, but if there is a problem codec, then this solution will remove the codec, and have Plex reinstall it again.

An alternative is to delete the codec you think Plex is trying to use to transcode the media file to see if that fixes this issue.

Summary

Plex Media Server installs and uses codecs on the server when it needs to transcode a media file to stream to a client. There may be times when the required codec is not installed.

There could be a few reasons why the codec is not installed, and this post detailed three fixes you can try to resolve this issue.

If the above three solutions didn't fix the codec issue, then the next step would be to try asking for solutions on the Plex forums.