3.1.5.2.2 Bulk AES Counter Mode
Bulk AES counter node is a simple counter encryption of the payload that uses a stream global AES counter. The transmitter MAY default to this mode on any given packet identifier (PID) if the receiver has not specified a mode.
With bulk AES counter mode, transport stream packets are encrypted by encrypting the 184 bytes after the first fixed 4 bytes of the transport stream header. If the transport stream packet has an adaptation field, that information is encrypted as well. The 184 bytes will use 11.5 AES encryption blocks. For bulk mode, the extra trailing 8 bytes of the AES counter mask that is not used in the XOR combining operation is to be retained and used at the beginning of the next transport stream packet, so that the processing of two contiguous packets will use 23 AES encryption blocks, as shown in the figure below.

Figure 8: AES Encryption Block
Content encrypted using bulk AES counter mode is less efficient for PVR style usage. It requires that the receiver decrypt the content and potentially re-encrypt it at capture time, in addition to decrypting it at playback time. Streaming AES counter mode on audio/video PIDs saves the capture time decrypt and re-encrypt, but it requires more resources within the tuner to support, as such encryption needs to track per-PID state that is enabled for Streaming AES counter mode.
As such, bulk AES mode is used whenever Streaming AES counter mode is fully consumed, or for any PID that requires significant decryption at capture time.
As a general rule the receiver SHOULD prioritize the use of Streaming AES counter mode to PIDs that contain audio/video content. In addition, if the transmitter performs sufficient content screening it MAY also make this decision and automatically put audio/video content into Streaming AES counter mode.
In any case the transmitter is required to support at least 8 Stream AES counter mode PIDs.