# SCTE-35 messages for ad breaks
<a name="ca-scte-35-messages"></a>

With MediaTailor, you can create a content channel based off of source location and VOD source resources. You can then set up one or more ad breaks for each of the programs on a channel's schedule. You use messages based on the SCTE-35 specification to condition the content for ad breaks. For example, you can use SCTE-35 messages to provide metadata about the ad breaks. For more information about the SCTE-35 specification, see [Digital Program Insertion Cueing Message](https://webstore.ansi.org/Standards/SCTE/ANSISCTE352022).

You set up the ad breaks in one of two ways:
+ Attaching a `time_signal` SCTE-35 message with a `segmentation_descriptor` message. This `segmentation_descriptor` message contains more advanced metadata fields, like content identifiers, which convey more information about the ad break. MediaTailor writes the ad metadata to the output manifest as part of the `EXT-X-DATERANGE` (HLS) or `EventStream` (DASH) ad marker's SCTE-35 data.
+ Attaching a `splice_insert` SCTE-35 message that provides basic metadata about the ad break.
+ HLS:
  + When the Ad markup type is `Daterange`, MediaTailor specifies ad breaks as `EXT-X-DATERANGE` tags in the manifest.
  + When the Ad markup type is `Scte35 Enhanced`, MediaTailor specifies ad breaks using the following tags:
    + MediaTailor places an `EXT-X-CUE-OUT` on the first segment of the ad slate, indicating a cut from content to the ad break. It contains the expected duration of ad break, such as `EXT-X-CUE-OUT:Duration=30`.
    + `>EXT-X-ASSET`: This tag appears on the same segment as `EXT-X-CUE-OUT` and contains the ad-break metadata supplied in the AdBreak when the program is created or updated. It always contains `CAID`.
    + `EXT-OATCLS-SCTE35`: This tag appears on the same segment as `EXT-X-CUE-OUT` and contains base64-encoded bytes of the SCTE-35 message.
    + `EXT-X-CUE-OUT-CONT`: This tag appears on each subsequent segment within the ad slate, and contains duration and elapsed-time information. It also contains the base64-encoded SCTE-35 message, and the `CAID`.
    + `EXT-X-CUE-IN`: This tag appears on the first segment of content after the ad break is over, and indicates a cut from an ad break back to content.

The following illustration shows the two ways of setting up ad breaks in a channel using SCTE-35 messages:
+ Use a `splice_insert()` message to set up ad breaks with basic metadata.
+ Use a `time_signal()` message together with a `segmentation_descriptor()` message to set up ad breaks with more detailed metadata.

![\[Two ways of setting up ad breaks in a channel using SCTE-35 messages.\]](http://docs.aws.amazon.com/mediatailor/latest/ug/images/scte-35-splice-insert-vs-time-signal-segmentation-descriptor.png)


For information about using `time_signal`, see section 9.7.4 of the 2022 SCTE-35 specification, [Digital Program Insertion Cueing Message](https://webstore.ansi.org/Standards/SCTE/ANSISCTE352022).

The ad break information appears in the output `splice_info_section` SCTE-35 data. With MediaTailor, you can pair a single `segmentation_descriptor` message together with a single `time_signal` message.

**Note**  
If you send a `segmentation_descriptor` message, you must send it as part of the `time_signal` message type. The `time_signal` message contains only the `splice_time` field that MediaTailor constructs using a given timestamp.

The following table describes the fields that MediaTailor requires for each `segmentation_descriptor` message. For more information, see section 10.3.3.1 of the 2022 SCTE-35 specification, which you can purchased at the [ANSI Webstore website](https://webstore.ansi.org/Standards/SCTE/ANSISCTE352022).


**Required fields for a `segmentation_descriptor` message**  

| Field | Type | Default value | Description | 
| --- | --- | --- | --- | 
| segmentation\$1event\$1id | integer | 1 | This is written to segmentation\$1descriptor.segmentation\$1event\$1id. | 
| segmentation\$1upid\$1type | integer | 14 (0x0E) | This is written to segmentation\$1descriptor.segmentation\$1upid\$1type. The value must be between 0 and 256, inclusive. | 
| segmentation\$1upid | string | "" (empty string) | This is written to segmentation\$1descriptor.segmentation\$1upid. The value must be a hexadecimal string, containing characters 0-9 and A-F. | 
| segmentation\$1type\$1id | integer | 48 (0x30) | This is written to segmentation\$1descriptor.segmentation\$1type\$1id. The value must be between 0 and 256, inclusive. | 
| segment\$1num | integer | 0 | This is written to segmentation\$1descriptor.segment\$1num. The value must be between 0 and 256, inclusive. | 
| segments\$1expected | integer | 0 | This is written to segmentation\$1descriptor.segments\$1expected. The value must be between 0 and 256, inclusive. | 
| sub\$1segment\$1num | integer | null | This is written to segmentation\$1descriptor.sub\$1segment\$1num. The value must be between 0 and 256, inclusive. | 
| sub\$1segments\$1expected | integer | null | This is written to segmentation\$1descriptor.sub\$1segments\$1expected. The value must be between 0 and 256, inclusive. | 

The following table shows the values that MediaTailor automatically sets for some of the `segmentation_descriptor` message's fields.


**Values set by MediaTailor for a `segmentation_descriptor` message's fields**  

| Field | Type | Value | 
| --- | --- | --- | 
| segmentation\$1event\$1cancel\$1indicator | Boolean | True | 
| program\$1segmentation\$1flag | Boolean | True | 
| delivery\$1not\$1restricted\$1flag | Boolean | True | 

MediaTailor always sets the `segmentation_duration_flag` to `True`. MediaTailor populates the `segmentation_duration` field with the duration, in ticks, of the state content.

**Note**  
When MediaTailor sends the `time_signal` messages, it sets the `splice_command_type` field in the `splice_info_section` message to 6 (0x06).

In HLS output, for an `AdBreak` with a `time_signal` message, the output `EXT-X-DATERANGE` tag includes a `SCTE-35` field that is set to the serialized version of the `splice_info_section` message. For example, the following `EXT-X-DATERANGE` tag shows the serialized version of the `splice_info_section` message:

```
#EXT-X-DATERANGE:ID=\"1\",START-DATE=\"2020-09-25T02:13:20Z\",DURATION=300.0,SCTE35-OUT=0xFC002C00000000000000FFF00506800000000000160214435545490000000100E000019BFCC00E0030000000000000
```

In DASH output, for an `AdBreak` with a `time_signal` message, the output `EventStream` element includes a `scte35:SpliceInfoSection` element with `scte35:TimeSignal` and `scte35:SegmentationDescriptor` elements as its children. The `scte35:TimeSignal` element has a child `scte35:SpliceTime` element, and the `scte35:SegmentationDescriptor` element has a child `scte35:SegmentationUpid` element. For example, the following DASH output shows the `EventStream` element's child element structure:

```
<EventStream schemeIdUri="urn:scte:scte35:2013:xml" timescale="90000">
    <Event duration="27000000">
        <scte35:SpliceInfoSection protocolVersion="0" ptsAdjustment="0" tier="4095">
            <scte35:TimeSignal>
                <scte35:SpliceTime ptsTime="0" />
            </scte35:TimeSignal>
            <scte35:SegmentationDescriptor segmentNum="0" segmentationDuration="27000000" segmentationEventCancelIndicator="false" segmentationEventId="1" segmentationTypeId="48" segmentsExpected="0">
                <scte35:SegmentationUpid segmentationUpidFormat="hexBinary" segmentationUpidType="14">012345</scte35:SegmentationUpid>
            </scte35:SegmentationDescriptor>
        </scte35:SpliceInfoSection>
    </Event>
</EventStream>
```

You learned about using SCTE-35 messages to set up ad breaks in channel assembly, the structure and required fields for those messages, and sample HLS and DASH output that includes the SCTE-35 messages.