Playing pre-roll from the middle of the content (continue watching)

[kotucz]

0 --------- 1 ---------2 ---- CW --- 3 ---- 4 ----

Imagine in the timeline above, user reopens the content and continues watching (CW) from the somewhere in the middle.
We want to play preroll upon opening the content. When user seeks to the beginning and plays or seeks through ad groups 1 and 2, we want the ad groups play.

What is the recommended approach for doing this?

We are using custom AdsLoader implementation.

From our attempts so far we found this:

When the ad groups are initialized as in the scheme above, player will pick ad group 2 to be played instead of preroll group 0. As per AdPlaybackState.getAdGroupIndexForPositionUs

ExoPlayer 2.16.1
Number of ad groups may not change, but ad group times can change. So we can move groups 1 and 2 to some different position and restore when seeking back.

In later media3 versions
Ad groups may not change time:

AdPlaybackState.checkValidAdPlaybackStateUpdate
checkState(oldAdGroup.timeUs == newAdGroup.timeUs);

Midroll ad groups may be added later (after playing preroll) but this causes position discontinuity and buffering

I am thinking of rearranging the ad groups and inserting preroll ad group at CW position instead of 0, but this seems quite error-prone

Is there some other way to implement this, that I am missing? Thanks

[marcbaechinger]

Thanks for your report!

Yeah, I agree that based on the current implementation ad 3 would be played as you say.

AdPlaybackState.checkValidAdPlaybackStateUpdate
checkState(oldAdGroup.timeUs == newAdGroup.timeUs);

I wasn't aware of this inconsistency. Thanks for mentioning this. We can investigate if we can remove the check for timeUs. I think currently this is the safe bet, It makes sure that no ad groups have changed/swapped position. It may be that the timeUs check may be not needed. Not sure without further analysis.

We are using custom AdsLoader implementation.
Is there some other way to implement this, that I am missing? Thanks

I think you could initially call adPlaybackState.withSkippedAd(adGroupIndex) for all ads before CW except 0 which is the preroll. When playback starts after this change, then the user would see the preroll and then the playback resumes at the position where the user landed. Once this has happened you can call adPlaybackState.withAvailableAdMediaItem() again for the ads that have been skipped.

I haven't tried but I think from looking at the code these two operations are both valid.

Would that work for your use case and have you tried this option?

[kotucz]

I think when ad groups 1 and 2 are skipped, and preroll at 0 is available, it won't be played.

AdPlaybackState: 

  public int getAdGroupIndexForPositionUs(long positionUs, long periodDurationUs) {
    // Use a linear search as the array elements may not be increasing due to TIME_END_OF_SOURCE.
    // In practice we expect there to be few ad groups so the search shouldn't be expensive.
    int index = adGroupCount - 1;
    index -= isLivePostrollPlaceholder(index) ? 1 : 0;
    while (index >= 0 && isPositionBeforeAdGroup(positionUs, periodDurationUs, index)) {
      index--;
    }
    return index >= 0 && getAdGroup(index).hasUnplayedAds() ? index : C.INDEX_UNSET;
  }

It will find ad group 2. It is skipped -> hasUnplayedAds() = false -> C.INDEX_UNSET. No ad group would be played.
Once user seeks e.g. between ad groups 1 and 2. We would mark ad group 2 AVAILABLE to be played later.

Up until now, the our implementation was that ad groups 1 and 2 would never be created (and played), so preroll playback was no issue.

Also what is the requirement, that if ad group is added, there is a discontinuity created?
I think I traced it up to here:
ExoPlayerImplInternal.resolvePositionForPlaylistChange

    boolean earliestCuePointIsUnchangedOrLater =
        periodIdWithAds.nextAdGroupIndex == C.INDEX_UNSET
            || (oldPeriodId.nextAdGroupIndex != C.INDEX_UNSET
                && periodIdWithAds.nextAdGroupIndex >= oldPeriodId.nextAdGroupIndex);

and onlyNextAdGroupIndexIncreased

I do not understand why content source needs to buffer again after adding new playable ad group in the future. But maybe this is for another question...

I mean if I start with preroll only and create the midroll ad groups afterwards (1, 2 - skipped and 3, 4 - available). It would work, but player starts buffering, so this is also negative user experience, which I am trying to avoid.

Thanks