Grass Valley K2 Media Client System Guide Oct.10 2006 - Manual (Page 35)

September 7, 2006 K2 Media Client System Guide 35
Video loopback
the Windows file system) that controls access to the raw data that makes up each
file. Any reading and writing of clips, be it through play and record operations or
through file transfers and media streaming, is managed by the database. The
database and file system run as Windows programs.
The Storage system includes the media disk drives, controllers, drivers, and adapters
necessary for access and movement of the data. While the primary data flow is within
the overall control of the Real Time system, some components and their
communication pathways cross over into the Application system. For example, the
RAID controller board plugs into the motherboard and accesses media drives in
internal storage models, yet it is controlled by Windows. The media drives appear as
the V: drive to the Windows operating system.
The Real Time system manages the media flow between the Storage system and the
inputs and outputs. The Real Time system has a dedicated processor and
time-sensitive mechanisms to serve media processing needs while maintaining
real-time accuracy.
When you control play and record operations from within the Application system you
trigger a chain of events that eventually crosses over into the Real Time system and
results in media access. The following sequence is an example of this type of chain of
events:
1. A user operates the Player application to play a particular clip. The Player
application asks the Media File system for permission to access the clip. The Media
File system grants access. In external storage models, the Media File system
enforces shared storage policies in order to grant the access. When access is
granted, the Player application initiates play access to the clip.
2. The database identifies the files that make up the clip and the file system instructs
the Storage system to open access to the files.
3. The Storage system finds the raw data and opens the appropriate read access. At
this point both the Application system and the Real Time system are involved.
Windows controls the media drives and controllers, so the Real Time system
makes file requests to Windows and it causes the data to be transferred to buffers
on the Real Time processor. The data is then available to the Real Time system so
that it can be processed at exactly the right time.
4. The Real Time system processes the media, decompresses it, adjusts its timing, and
moves it as required to play the clip as specified by the user.
Video loopback
On SD-only models, the video, AES, and LTC inputs pass to the their output
connectors as loop through. This is on record channels only.
On HD/SD models, you can monitor the video that is being recorded. The video is
routed back essentially untouched. Any ancillary data or embedded audio that is on
the input video is still there on the loopback. The K2 system and the loop-back videos
must be locked to a video reference for the loop-back feature to work properly.
NOTE: The loopback path is for monitoring purposes only.