- Dynamic label,
- MOT (Multimedia Object Transfer) data group,
- MOT CA (Conditional Access) messages.
In AAC the X-PAD and F-PAD (Fixed PAD) are at the beginning of the audio frame. 
As presented in the Figure 1, PAD field is divided between fixed and extra PAD field. F-PAD field is always present, as it carries information about the X-PAD. If X-PAD data is not present,
X-PAD Ind field within the F-PAD is set to
00. Additionally, if no information is carried within the F-PAD field, its content shall be set to
If X-PAD data group is present, first two bits of the F-PAD shall be set to
00. Next two bits (
X-PAD Ind) carry information about type of X-PAD field: none, short or variable size.
CI flag set to
1 means that there will be CI (Content Indicator) field. Last bit shall be set to
CI fields are used to carry information about application type being sent, and in case of variable size X-PAD, about its length. If no CI field is present, application type and length are identical to last X-PAD data group.
Short X-PAD has a fixed length of 4 bytes and can contain at most one CI field.
Variable size X-PAD has length between 4 and 196 bytes. It can contain up to four CI fields. Application type 0 (End marker) is used to terminate the CI list.
|1||Data group length indicator|
|2||Dynamic label segment, start of X-PAD data group|
|3||Dynamic label segment, continuation of X-PAD data group|
|4 to 11||User defined|
|12||MOT, start of X-PAD data group, see EN 301 234 |
|13||MOT, continuation of X-PAD data group, see EN 301 234 |
|14||MOT, start of CA messages, see EN 301 234 |
|15||MOT, continuation of CA messages, see EN 301 234 |
|16 to 30||User defined|
Figure 3 illustrates example data group. Every data group must start with Application type 1, which carries length of the following data group as presented in table 1. Next, start segment must be sent (application type 2, 12, 14). Then come the continuation segments.
- ETSI EN 300 401
- ETSI TS 102 563
- ETSI EN 301 234