fix: derive timelapse duration from compiled video by samdev-7 · Pull Request #192 · hackclub/lapse

samdev-7 · 2026-04-03T17:44:49Z

Summary

The duration field was computed from snapshot timestamps with a 120s idle timeout filter, which often diverged from the actual video length (ratios of 75x–162x instead of expected 60x)
Now when the realize worker compiles a video, it returns the measured video duration (already computed via ffprobe for thumbnail generation) and the server overwrites duration with videoDuration × 60
Guards recalculateDurations admin endpoint to only target unrealized timelapses, preserving video-derived durations

Test plan

Publish a test timelapse and verify duration / 60 ≈ video_length in the API response
Confirm worker logs include videoDuration in the job completion output
Confirm recalculateDurations only updates timelapses with s3Key: null
Verify in-flight jobs (without videoDuration) still complete without error

The `duration` field was computed from snapshot timestamps using a 120-second idle timeout filter, which often diverged from the actual video length. This caused ratios of 75x-162x instead of the expected 60x between `duration` and video length. Now when the realize worker finishes compiling a video, it returns the measured video duration (already computed for thumbnail generation) and the server overwrites `duration` with `videoDuration * TIMELAPSE_FACTOR`. Also guards `recalculateDurations` to only target unrealized timelapses, preserving video-derived durations for completed ones.

Copilot

Pull request overview

Adjusts how published timelapse duration is derived so API-reported real-time duration matches the compiled video length (instead of relying on snapshot timestamp heuristics), and prevents the admin duration recalculation endpoint from overwriting video-derived durations.

Changes:

Extend realize job outputs to include optional videoDuration (seconds) measured via ffprobe.
Have the worker return videoDuration, and have the server persist duration = videoDuration × TIMELAPSE_FACTOR on job completion when present.
Restrict the recalculateDurations admin endpoint to only update unrealized timelapses (s3Key: null).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
packages/jobs/src/realize.ts	Adds `videoDuration` to the realize job output schema for server-side persistence.
apps/worker/src/workers/realize.ts	Captures and returns `videoDuration` alongside the video/thumbnail S3 keys.
apps/server/src/routers/admin.ts	Limits duration recalculation to unrealized timelapses and updates log messaging.
apps/server/src/job.ts	Persists video-derived duration on realize completion and logs `videoDuration`.

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Copilot · 2026-04-03T17:50:09Z

packages/jobs/src/realize.ts

+     * The duration of the compiled output video in seconds, as measured by ffprobe.
+     * Optional for backwards compatibility with in-flight jobs that predate this field.
+     */
+    videoDuration: z.number().nonnegative().optional()


videoDuration is validated as nonnegative(), which allows 0, but measureVideoDuration() throws for duration <= 0. Consider using positive() (or finite().positive()) here so the schema matches the actual invariant and rejects zero/NaN values.

Suggested change

videoDuration: z.number().nonnegative().optional()

videoDuration: z.number().finite().positive().optional()

Copilot · 2026-04-03T17:50:10Z

apps/server/src/routers/admin.ts

+            // Only recalculate durations for timelapses that haven't been realized yet.
+            // Realized timelapses have their duration set from the compiled video, which is the source of truth.
            const PAGE_SIZE = 100;
            let updated = 0;
            let cursor: string | undefined;

            while (true) {
                const batch = await database().timelapse.findMany({
                    select: { id: true, snapshots: true },
+                    where: { s3Key: null },


This endpoint now explicitly skips realized timelapses (where: { s3Key: null }), but the public admin contract/docs still describe it as “recalculates the duration of every timelapse from its snapshots”. Please update the API contract description (and/or rename/add params) so callers aren’t misled about what will be updated.

Copilot · 2026-04-03T17:50:10Z

apps/server/src/job.ts

                data: {
                    associatedJobId: null,
                    s3Key: videoKey,
-                    thumbnailS3Key: thumbnailKey
+                    thumbnailS3Key: thumbnailKey,
+                    ...(videoDuration != null && { duration: videoDuration * TIMELAPSE_FACTOR })
                },


Duration is derived using a runtime TIMELAPSE_FACTOR import. Since the server and worker ship as separate images, a version-skew deploy could result in the worker encoding with one factor while the server multiplies by another, permanently storing the wrong duration. To make this robust, consider having the worker return the factor used (or the already-multiplied real-time duration) and use that value for the DB update.

The `duration` field was computed from snapshot timestamps using a 120-second idle timeout filter, which often diverged from the actual video length. This caused ratios of 75x-162x instead of the expected 60x between `duration` and video length. Now when the realize worker finishes compiling a video, it returns the real-time duration (videoDuration * TIMELAPSE_FACTOR, computed worker- side to avoid version-skew issues) and the server stores it directly. Also guards `recalculateDurations` to only target unrealized timelapses, preserving video-derived durations for completed ones.

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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

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Copilot · 2026-04-03T18:08:26Z

packages/jobs/src/realize.ts

+     * The real-time duration of the timelapse in seconds (i.e. `videoDuration * TIMELAPSE_FACTOR`),
+     * as measured by ffprobe on the compiled output video. This value can be stored directly as the
+     * timelapse `duration` without further conversion.


The JSDoc for realTimeDuration is a bit contradictory: ffprobe measures the compiled video’s duration (videoDuration), but realTimeDuration is a derived value after multiplying by TIMELAPSE_FACTOR. Consider updating the comment to explicitly say it’s derived from the ffprobe-measured duration (or alternatively rename/expose the raw videoDuration separately) to avoid confusing future consumers about units/source-of-truth.

Suggested change

* The real-time duration of the timelapse in seconds (i.e. `videoDuration * TIMELAPSE_FACTOR`),

* as measured by ffprobe on the compiled output video. This value can be stored directly as the

* timelapse `duration` without further conversion.

* The real-time duration of the timelapse in seconds, derived as

* `videoDuration * TIMELAPSE_FACTOR` from the compiled output video's duration measured by ffprobe.

* This value can be stored directly as the timelapse `duration` without further conversion.

Copilot · 2026-04-03T18:08:26Z

apps/worker/src/workers/realize.ts

            return {
                timelapseId,
                videoKey,
-                thumbnailKey
+                thumbnailKey,
+                realTimeDuration: videoDuration * TIMELAPSE_FACTOR
            };


realTimeDuration is being returned as videoDuration * TIMELAPSE_FACTOR (i.e., already converted to the timelapse’s “real-time” duration). Given the PR description talks about returning the measured videoDuration and letting the server multiply by 60, it would be clearer to either (a) return the raw videoDuration and do the conversion server-side, or (b) rename this field to something that makes it obvious it’s already in timelapse-duration seconds (and optionally log/return both values).

Copilot · 2026-04-03T18:08:27Z

packages/api/src/contracts/admin.ts


    recalculateDurations: contract("POST", "/admin/recalculateDurations")
-        .route({ description: "Recalculates the duration of every timelapse from its snapshots. Requires administrator permissions and an `elevated` grant." })
+        .route({ description: "Recalculates the duration of unrealized timelapses (those still processing, without a compiled video) from their snapshots. Realized timelapses are skipped because their duration is derived from the compiled video. Requires administrator permissions and an `elevated` grant." })


The updated route description says unrealized timelapses are “those still processing”, but the server-side filter is where: { s3Key: null }, which will also include timelapses that are no longer processing (e.g. FAILED_PROCESSING with associatedJobId: null). Consider tweaking the description to match the actual criterion (“no compiled video / s3Key is null”) rather than “still processing”.

Suggested change

.route({ description: "Recalculates the duration of unrealized timelapses (those still processing, without a compiled video) from their snapshots. Realized timelapses are skipped because their duration is derived from the compiled video. Requires administrator permissions and an `elevated` grant." })

.route({ description: "Recalculates the duration of unrealized timelapses (those without a compiled video, where `s3Key` is null) from their snapshots. Realized timelapses are skipped because their duration is derived from the compiled video. Requires administrator permissions and an `elevated` grant." })

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Lamparter · 2026-04-03T19:48:43Z

thank you!

samdev-7 requested a review from Copilot April 3, 2026 17:45

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samdev-7 requested a review from Copilot April 3, 2026 18:04

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fix: clarify realTimeDuration JSDoc, admin description, and add worke…

257d682

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samdev-7 requested a review from Copilot April 3, 2026 19:24

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ascpixi merged commit 87b7efa into main Apr 3, 2026
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fix: derive timelapse duration from compiled video#192

fix: derive timelapse duration from compiled video#192
ascpixi merged 3 commits intomainfrom
fix/duration-from-video

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	videoDuration: z.number().nonnegative().optional()
	videoDuration: z.number().finite().positive().optional()

	.route({ description: "Recalculates the duration of unrealized timelapses (those still processing, without a compiled video) from their snapshots. Realized timelapses are skipped because their duration is derived from the compiled video. Requires administrator permissions and an `elevated` grant." })
	.route({ description: "Recalculates the duration of unrealized timelapses (those without a compiled video, where `s3Key` is null) from their snapshots. Realized timelapses are skipped because their duration is derived from the compiled video. Requires administrator permissions and an `elevated` grant." })

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samdev-7 commented Apr 3, 2026

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