Grass Valley iTX System v.2.6 - Manual (Page 261)

The Media Cache Service
Skipping of missing media files
In progressing through a schedule, TXPlay skips any event for which the required media file is
not in the system. If the media file later becomes available, TXPlay sends a cache request for it
to the Media Cache Service.
Interruption to caching
The Media Cache Service receives cache requests from TXPlay for one event at a time in
schedule order. Once it starts a job, unless it is interrupted to do a higher-priority job, it
continues until caching is complete. It does this even if the event that requires the media file
being cached is deleted from the schedule.
If the live schedule is modified in a way that causes a media file for an earlier event to require
caching, the Media Cache Service stops the current job and starts the caching operation for the
earlier event. On finishing this, the service continues to process jobs in schedule order.
If a new schedule is loaded in the playout channel and it contains no event that requires the
media file currently being cached, the Media Cache Service stops caching the file. It then starts
caching for the new schedule.
Cache management
When there is not enough free space in the cache for the next media file that needs to be
added, the Media Cache Service has to make space; it does this by deleting media files that are
no longer required.
In determining which files to delete, it first identifies those files for which there are no schedule
requirements. From these, it selects the one that was least recently scheduled and deletes it; it
selects and deletes other files in the same way until there is enough free space for the required
file.
In the Schedule Grid, when there is insufficient cache space, the cache status indicator for the
event that the Media Cache Service is attempting to cache the media file for shows red [  ].
Note:
• The Media Cache Service does not delete cached media files that are required by
events later than the one it is processing.
This may cause it to be unable to make enough space for a particular media file; iTX
then has to play out a media file from the Media Store. To prevent such a situation,
the cache should be set up with a capacity large enough to meet the requirements of
the most demanding schedule.
Caching in a multi-domain system
In a multi-domain system, the Media Cache Service uses the OPUS 2 Service to search the local
domain for a required media item. If the OPUS 2 service cannot find the media item there, it
searches other domains – in the configured order (see below, "Search order of domains in
multi-domain caching") – until it finds the media item. The Media Cache Service then passes
the media-file location details to TXPlay.
March 2015 System Administrator Guide Page 261 of 404