Definition: The KAG is the KLV Alignment Grid a performance optimization technique.

Description: To create efficient MXF systems that involve storage, it is important to be able to define the byte alignment of the stored data. Many storage media such as hard disks are organized in fixed-size sectors and system speed, and efficiency can be improved if applications read and write integer numbers of sectors to fetch essence. MXF, however, is a generalized file format and there is no single sector size that is the optimum for all applications. Uncompressed HD applications work best with very big sectors; however, this can become very inefficient for low bitrate streams such as audio.

MXF defined a property called the KLV Alignment Grid (KAG). It is a UInt32 property of the Partition Pack and defines the desired byte alignment of the start of essence elements within a partition. It is possible to have many partitions in a file, each with a different KAG size, but this is not recommended. Higher operational patterns (particularly those in the b row) may have different essence containers, each of which has a different optimal KAG. For example, Figure 3.13 shows a partition with high data rate picture essence and another with low date rate sound essence. For overall system performance, there should be an integer relationship between all the KAG values, and the file overall should respect the smallest of these KAG values.

Figure 3.13: Multiple KAG values in an OP1b file