Pre-rolls in DAI live streams (Beta)

In Ad Manager, you can configure a live stream event for pre-rolls.

1. Sign in to Google Ad Manager.

2. Navigate to Video, then Live streams.

3. Click New live stream.

4. Set "Pre-roll ad break settings" to Enabled.

5. Enter your ad tag. If you do not have one, you can click Create tag to set one up.

6. Enter the maximum pre-roll duration. This value must be between 1 second and 10 minutes.

7. Complete the remaining live stream event settings.

8. Click Save and activate.

To view the pre-roll, create a new stream session for the new live stream event in a player. The pre-roll should play before content unless it coincides with a mid-roll, in which case the mid-roll will be shown instead.

Requirements

The following are requirements for MPEignoredDASH and HLS:

MPEignoredDASH

• Audio and video segments should align as closely as possible to allow trimming at any point in the MPD.
• All segments must start with a Stream Access Point (SAP) and should convey that by setting @startWithSAP to a non-zero value on the MPD's AdaptationSets and Representations.

HLS

• Audio and video segments should align as closely as possible to allow trimming at any point in the manifest.
• All segments must start with a keyframe (that is, be decodable without information from other segments). This should be conveyed with the #EXT-X-INDEPENDENT-SEGMENTS tag in the master playlist or all media playlists.
• For pre-roll ads to render, the underlying content stream must provide consistent timestamps through #EXT-X-PROGRAM-DATE-TIME tags. Inserting the tags at the top of each variant playlist and after each discontinuity is recommended. Failure to provide these tags causes DAI decisioning of the pre-roll ads, but not stitching them into the playlist.

Pre-roll expectations

Publishers can expect the following pre-roll behaviors for both MPEignoredDASH and HLS:

MPEignoredDASH

• A pre-roll's start time is determined by using the stream session's create timestamp and subtracting the greater value between 3 * @maxSegmentDuration and @suggestedPresentationDelay.
• The pre-roll is not rendered based on the first request of the media presentation description for DASH (MPD). This means that if the client player doesn't begin to request the manifest immediately after beginning the stream, the pre-roll may not play correctly or at all.
• The top of the content at the current snapshot is trimmed and included after the pre-roll. Eventually, the pre-roll "falls off" the top of the supplied digital video recorder (DVR) window.
• No content is rendered before the first pre-roll segment. "Seeking back" before the pre-roll is not supported. The DVR window starts growing after the pre-roll. After the end of the pre-roll pod, the stream transitions to the live content. Eventually, the pre-roll "falls off" the top of the DVR window configured in the live stream settings.
• The pre-roll is not affected by ad holidays.
• DAI may stitch slate with a duration up to one content segment's length after the pre-roll to maintain the stream timeline.
• The pre-roll will be skipped if it overlaps with a mid-roll. To avoid this behavior, use the dai-pre stream creation parameter override, set to 1 (dai-pre=1). When pre-roll plays instead of an overlapping mid-roll and the mid-roll extends past the pre-roll, the mid-roll will instead be replaced with slate or underlying content, depending on the empty ad break fill type setting for the event.

HLS

• The pre-roll's start time is determined by using the stream session's create timestamp and subtracting 2.5x TARGET-DURATION intervals. 
• The pre-roll is not rendered based on the first request of the HLS manifests. This means that if the client player doesn't begin requesting the manifest immediately after beginning the stream, the pre-roll may not play correctly or at all. 
• No content is rendered before the first pre-roll segment. "Seeking back" before the pre-roll is not supported. The DVR window starts to grow after the pre-roll. After the end of the pre-roll pod, the stream transitions to the live content. Eventually, the pre-roll "falls off" the top of the DVR window configured in the live stream settings.
• The pre-roll is not affected by ad holidays.
• DAI may stitch slate with a duration up to one content segment's length after the pre-roll to maintain the stream timeline.
• The pre-roll will be skipped if it overlaps with a mid-roll. To avoid this behavior, use the dai-pre stream creation parameter override, set to 1 (dai-pre=1). When pre-roll plays instead of an overlapping mid-roll and the mid-roll extends past the pre-roll, the mid-roll will instead be replaced with slate or underlying content, depending on the empty ad break fill type setting for the event.