By Atom Trujillo

Premiere Pro's media cache consist of files that assist Premiere in locating, managing, and understanding media within projects.

On every import into a Premiere Pro project, media cache files are created and stored locally for Premiere to use.

A problem is, after a time, the media cache can eat up a large portion of your hard drive.  It may also become corrupt causing inconsistency in playback and performance issues;  it’s sometimes beneficial to purge the cache and start over.

Location, Location, Location

It’s optimal to have the media cache reside on the fastest drive possible; SSD, or a RAID’d drive.  These files are accessed very frequently by Adobe; so the faster the drive, the better.

As you can see from the graph below, opening a very large Premiere project; 130MB+ project file, 10,000+ assets, with empty cache folders.  An SSD drive used as the media cache has a significant advantage over spinning disk drives.

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*Timed from opening of project, till completion of asset indexing, with no media showing as pending, project in a fully working state with no background tasks running. Automatic peak file generation was disabled. No conforming needed with assets.

Move to a more convenient location: It may be a good idea to move the cache to a more easily accessed folder. At the very least, be aware of where they are being stored, in the event you need to manually purge the cache. Purging the cache will be discussed later.

Default location for media cache are as followed: 
Mac: /Users/Library/Application Support/Adobe/Common
Windows: \Users\<username>\AppData\Roaming\Adobe\Common

There are two important folders within the cache:

Media Cache files folder is the directory storing the cache files.

Media Cache Database folder maintains a list and link to every file imported into Premiere.

File extensions:

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.cfa - These are audio conform files, these files can get quite large, and will fill up your drive. You’ll want to keep an eye on these files, if you start running low on disk space. Premiere creates these files for any compressed audio imported into a project.

They are uncompressed versions of all your compressed audio, which Premiere can work with faster than the compressed version.

On initial import of media that requires conforming, if you look at the bottom right corner of your interface, you can see the conforming files progress.

.mcdb - loaded in the media cache folder, these files are links to every file you’ve ever imported into Premiere.

These files prevent Premiere from having to create redundant cache files when you import a file into multiple projects.

.ims - This a cache of file properties so that Premiere doesn’t have to re-scan each media file every time a project is opened.

.prmdc2 - These cache files are created per project file, not per media file.  They are metadata cache for the project file.

.pek - These files contain the visual representation of the audio waveforms you see in Premiere’s timeline and source monitor.  They were previously stored in the Media cache files folder.  With Premiere CC 2017 and above, these files are given their own dedicated Peak files folder.

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.mpgindex - these index files tell Premiere Pro where whole “I” frames exist in some MPEG-based files which helps Premiere understand how to interpret the non-whole frames that exist in a temporally- compressed formats.

.mxfassoc - Some MXF files have media attached to them or multiple media streams, this is a file that keeps tabs on those media associations.

Clean up!

The “clean” or in the latest version of Premiere, “clean unused” buttons force Premiere to search for every file you’ve ever imported into Premiere (using those .mcdb files).  If the application can still find the source media files, it keeps any associated cache files.  If it can no longer find the files, it deletes them. 

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These options aren’t very helpful if you’re working off a shared storage, or large drives where media isn’t deleted often.

The Great Purge: 

A manual deletion of these files/folders is sometimes needed to resolve corruption issues that can affect performance.

First, quit Premiere, navigate to the cache folders, select the media cache, and media cache folders, and delete.

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When you relaunch Premiere, and open a project, the media cache will be recreated.

Be aware that when relaunching a large project, you will need to give Adobe time to recreate the cache files.  Media may show as pending until this is completed.

If you’re experiencing issues with waveforms showing incorrectly, or not showing at all, you can also do the same with the Peak file folder.  Regeneration of the peak files can take a bit longer than the cache, so this shouldn’t be done as often.

It’s a good idea to clean the cache if you’ve been working on quite a few projects, if available disk space becomes an issue, or you notice performance issues within Premiere.

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