fix: bug in onTimelineGenerate: Use same time for "now" everywhere

[nytamin]

About the Contributor

This pull request is posted on behalf of the NRK.

Type of Contribution

This is a: Bug fix

Current Behavior

We have found a issue where the timings of pieces are not monotonic.
This only affects infinite pieces, and probably only when multiGatewayMode is enabled.

How to reproduce:

In a blueprints adlibAction:

// Stop the previous (infinite) piece
await context.stopPiecesOnLayers(['myLayer'])

await insertPiecesTyped(context, 'current', {
	[...],
	sourceLayerId: 'myLayer',
	enable: { start: 'now' },
	lifespan: PieceLifespan.OutOnShowStyleEnd,
})

This results in a virtual piece being inserted to stop the previous infinite OutOnShowStyleEnd piece, at time getCurrentTime()+calculateNowOffsetLatency (this is correct).
Then a pieceInstance is inserted at time "now", which is later resolved using getCurrentTime().
In our case, this ends up in that the virtual piece ends up after the inserted Piece, thus instantly ending it.

New Behavior

The same getCurrentTime()+calculateNowOffsetLatency time is used in both deNowifyMultiGatewayTimeline and in getTimelineRundown.

Testing

• I have added one or more unit tests for this PR
• I have updated the relevant unit tests
• No unit test changes are needed for this PR

Affected areas

This PR affects the playout logic in general.

Time Frame

• This is a critical bug for us, but not urgent to merge into upstream.

Other Information

Disclaimer: I have not gone through the other places where getCurrentTime() is used, so there might be other places calculateNowOffsetLatency should be used.

Status

• PR is ready to be reviewed.
• The functionality has been tested by the author.
• Relevant unit tests has been added / updated.
• Relevant documentation (code comments, system documentation) has been added / updated.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...s/job-worker/src/playout/timeline/multi-gateway.ts	0.00%	3 Missing ⚠️

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[nytamin]

@Julusian mentioned an issue with that we're now generating a now-time from a point-in-time before getTimelineRundown has run, which might cause issues since the variability in execution-time of getTimelineRundown will now play a part, which might not be ideal.

[Julusian]

As hinted above, I think that this will cause some timing issues.

This means that the targetNowTime used when de-nowifiying the timeline has the latency of playout-gateway included in the calculation, but not the latency of building the timeline.

When fixing up the multi-gateway mode, I intentionally kept the now values in the timeline with a deNowify step at the end to avoid this. This does cost some complexity, but allowed for keeping the shorted scoped latency.

So either:

1. This is the wrong solution, and the gap should be handled somewhere else
2. The latency calculation should be changed to measure the generation time too. This will concern me, as we call a few blueprint methods in there, and there is a lot of potential for O(n^2) or similarly non-linear latency variance