All about Pr Media Cache Files

The Mercury playback engine’s workings are kept secret by Adobe’s marketers. Recommended RAM is about three gigs per core you have on your system. Click here for Adobe’s official rendering & exporting notes.
While both Avid and FCPX support editing with native media, Premiere is designed around it. Adobe has not developed its own mezzanine, or intermediate, codec; while you can transcode media to, say, Apple’s ProRes or Avid’s DNxHD, it’s not necessary they say…
Playing anything without stutters from source or timeline depends on these four things:

1. Media has to be on a fast, local media drive (the faster the better, like 1000 MB/S  or better)
2. In Software-only a fast CPU with 8 cores or more.
Or in GPU Acceleration mode:
A combination of fast CPU & GPU with 1000+ cores & at least 4GB VRAM
3. Cache files & Database on a local, fast drive. (1000 MB/S or better)
4. Sequence settings have to match files on Timeline or Previews have to match delivery format.

When you bring in any footage that can’t be used as it’s own preview or cache file, Pr creates cache files in the background on import. After import playback is usually stuttery and audio drops out, but if you let it sit for a while, playback becomes smoother.
If you can use the media file as the preview file then Pr will not create cache files.
This is indicated by NO color in the Timeline.

This is the list of preferred I-Frame codecs that play without generating cache files:
DVCPRO-HD in MXF wrapper (the file structure on P2 cards)
DVCPRO-HD in Quicktime wrapper
PRORES >Any flavor (Mac only)
AVID DNxHD MXF (Adobe licensed for both Mac & PC)
AVID DNxHD in Quicktime wrapper
AVC-intra MXF (Mac & PC)
AVI (windows only)
Any other file will generate Cache files on import for both Video & Audio

By default both the cache files and the database are stored here:
Mac: /Users//Library/Application Support/Adobe/Common
Windows: \Users\<username>\AppData\Roaming\Adobe\Common
DO NOT LEAVE THEM THERE or you will run your editing system into the ground! The cache files can easily grow to 100GB or more. You have to manually delete them when a project is done and they also have to get rebuild in a multi-user-environment, because adobe does not support database or cache on shared storage.

files in Media cache folder:
.ims – Importer State files. These files refer to the sta- tus of an imported file.
.mxfassoc – MXF associations. Some flavors of MXF have media attached; some don’t. This cache keeps track of the associations.
.prmdc – Premiere Metadata Database Cache. This is a cache for the database.
.mpegindex – MPEG Index Files. Some types of MPEG files require their own index, like XDCAM.

AUDIO files in Media Cache folder:
.cfa – Conformed Audio. Most compressed formats have compressed audio, Pr builds an uncompressed version for them.
.pek – PEaK files. These PEaK files are a picture of the peaks that are turned into waveforms.
From Adobe >These rules determine which types of audio get conformed:

  • Premiere Pro does not conform audio in uncompressed clips that were recorded in one of the natively supported sample rates, when you use these clips in sequences with matching sample rates. 8000, 11025, 22050, 32000, 44100, 48000, 96000 Hz
  • Premiere Pro does conform audio in uncompressed clips when you use them in sequences with non-matching sample rates. However no conforming is done until you export the sequences or create audio preview files.
  • Premiere Pro does conform audio in uncompressed formats that were not recorded in a natively supported sample rate. In most of these cases, it will upsample the audio either to the nearest supported sample rate, or to a supported sample rate that is an even multiple of the source audio sample rate. For example, it will upsample an 11024Hz source to 11025Hz, since that is the nearest supported rate, and there is no supported rate that is an even multiple of 11024.
    See how the name of a Media Cache File indicates what was cached.

    From the Premiere manual:

    When Premiere Pro imports video and audio in some formats, it processes and caches versions of these items that it can readily access when generating previews. Imported audio files are each conformed to a new .cfa file, and MPEG files are indexed to a new .mpgindex file.
    The media cache greatly improves performance for previews, because the video and audio items do not need to be reprocessed for each preview. Note: When you first import a file, you may experience a delay while the media is being processed and cached.
    A database retains links to each of the cached media files. This media cache database is shared with Adobe Media Encoder, After Effects, Premiere Pro, and Audition, so each of these applications can each read from and write to the same set of cached media files. If you change the location of the database from within any of these applications, the location is updated for the other applications, too. Each application can use its own cache folder, but the same database keeps track of them.
    Choose Edit > Preferences > Media (Windows) or
    Premiere Pro > Preferences > Media (Mac OS), and do one of the following:
    To move the media cache or the media cache database, click the respective Browse, button.
    To remove conformed and indexed files from the cache and to remove their entries from the database, click Clean. This command only removes files associated with footage items for which the source file is no longer available.
 Before clicking the Clean button, make sure that any storage devices that contain your currently used source media are connected to your computer. If footage is determined to be missing because the storage device on which it is located is not connected, the associated files in the media cache is removed. This removal results in the need to reconform or reindex the footage when you attempt to use the footage later.
    Cleaning the database and cache with the Clean button does not remove files that are associated with footage items for which the source files are still available. To manually remove conformed files and index files, navigate to the media cache folder and delete the files.



Multi-track audio exports Premiere CC 2014 & 2015

The audio export is different between 2014 & 2015, make sure to follow the right instructions.
1. Match-frame a piece of footage in your sequence that matches the sequence settings. (keep it loaded into source window until step 4)
2. Select all on your sequence and Copy.
3. In the project window click “new Sequence” > choose any format, click the Tracks button> choose multichannel and the amount of tracks you need.multi14-1
4. Drag the footage from the source window in step 1, down into the sequence and “Change sequence settings”multi14-2
If you don’t get this warning undo and drag (the only way to get this message)
5. Delete the clip you just dragged (NOT UNDO)
6. Paste
You now have a sequence that matches the original sequence with the same content & settings but multi track audio instead of stereo.
7. Window> Audio Track Mixer
Assign the tracks from your sequence to the correct output channels.
8. Test the assignment by:
A. Turning on all-audio-channel-playback on your system (click to make all speakers blue under meters)
B. Solo the tracks you want to listen to and make sure they are panned correct.
Example: Music should be panned left/right, dialog can come out of 2 channels.
It really depends on your delivery specs. Here is a sample template for track assignment:
1+2 VO
3+4 SOT
5+6 FX (usually stereo)
7+8 MUSIC (stereo)
9. Un-solo all tracks after testing and choose: File>Export>Media
First switch to your export preset of choice (for the video)
Then click the Audio tab and choose:
Channels: >The number of channels you need to export from step 3
Audio Track Layout > x Mono Tracks
Channel Layout > Mono
This will create a quicktime with multiple Mono tracks, the universal format for delivering multi-track exports.