diff --git a/REUSE.toml b/REUSE.toml
index 2d928bc9df..7223df8518 100644
--- a/REUSE.toml
+++ b/REUSE.toml
@@ -9,6 +9,21 @@ precedence = "closest"
 SPDX-FileCopyrightText = "2026 Lusoris"
 SPDX-License-Identifier = "EUPL-1.2"
 
+# The run-result timeline schema, its fixtures, its test and its docs page are
+# contributor-authored (PR #2452): the fork-local EUPL-1.2 default applies,
+# credited to their author.
+[[annotations]]
+path = [
+    "api/run-result-timeline.schema.json",
+    "api/testdata/run-result-timeline/*.json",
+    "changelog.d/added/run-result-timeline-schema.md",
+    "docs/api/run-result-timeline.md",
+    "scripts/ci/tests/test_run_result_timeline_schema.py",
+]
+precedence = "closest"
+SPDX-FileCopyrightText = "2026 luoye-cpu"
+SPDX-License-Identifier = "EUPL-1.2"
+
 # These six files descend from Netflix/vmaf root files.  ADR-1250 requires
 # inherited work, and every fork contribution to it, to remain on the terms it
 # already carried rather than being swept into the fork-local EUPL default.
diff --git a/api/run-result-timeline.schema.json b/api/run-result-timeline.schema.json
new file mode 100644
index 0000000000..7abea8de21
--- /dev/null
+++ b/api/run-result-timeline.schema.json
@@ -0,0 +1,165 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://github.com/VMAFx/vmafx/api/run-result-timeline.schema.json",
+  "title": "VMAFx run-result timeline, schema version 1",
+  "description": "One versioned report format for a scoring run's provenance, per-frame scores, per-window statistics and events (VMAFx/vmafx#2452, RC5). It evolves additively under HISS-14: after a release, members are added, never removed, renamed or retyped; schema_version is the integer the document was written against, and a reader refuses a version it does not know by name. docs/api/run-result-timeline.md is the human reference. The skeleton pins the four sections' identities, not yet their full field contracts: provenance is the record of vmafx_context_provenance_json() (RC4 WP5, #2288; the authoritative field contract is the OpenAPI Provenance schema in api/openapi/vmafx-server-v1.yaml and the VmafxProvenance definition in core/api/vmafx.toml), and scoring_configuration is the option surface of #2258 (the scoring component group of the same OpenAPI document). The C ABI writer/reader and the byte-equal write-read-write identity check land in the follow-up PRs of the same issue.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "schema_version",
+    "provenance",
+    "frames",
+    "windows",
+    "events"
+  ],
+  "properties": {
+    "schema_version": {
+      "const": 1,
+      "description": "The schema version the document was written against. 1 is the shape this file defines; a reader refuses an unknown version by name (#2452 acceptance)."
+    },
+    "provenance": {
+      "$ref": "#/$defs/provenance"
+    },
+    "scoring_configuration": {
+      "$ref": "#/$defs/scoring_configuration"
+    },
+    "frames": {
+      "type": "array",
+      "description": "The per-frame series, in ascending time-key order: one entry per scored frame.",
+      "items": {
+        "$ref": "#/$defs/frame_score"
+      }
+    },
+    "windows": {
+      "type": "array",
+      "description": "Per-window statistics over ranges of the timeline: pooling and aggregation results.",
+      "items": {
+        "$ref": "#/$defs/window_statistic"
+      }
+    },
+    "events": {
+      "type": "array",
+      "description": "The run's events, in ascending time-key order: alignment decisions, drops, repeats, freezes, switches and masked areas.",
+      "items": {
+        "$ref": "#/$defs/event"
+      }
+    }
+  },
+  "$defs": {
+    "time_key": {
+      "description": "Where an entry sits on the timeline: at least one of the 0-based frame index, the presentation timestamp in nanoseconds from the run's zero, or the SMPTE-style timecode. A writer carries what the run knows - a frame score carries the frame index, a wall-clock event carries the timestamp - and an empty time key is refused.",
+      "type": "object",
+      "additionalProperties": false,
+      "anyOf": [
+        { "required": ["frame_index"] },
+        { "required": ["timestamp_ns"] },
+        { "required": ["timecode"] }
+      ],
+      "properties": {
+        "frame_index": {
+          "type": "integer",
+          "minimum": 0,
+          "description": "0-based display order, the stream-metadata display_index of api/stream-metadata-fields.json."
+        },
+        "timestamp_ns": {
+          "type": "integer",
+          "minimum": 0,
+          "description": "Presentation timestamp in nanoseconds from the run's zero."
+        },
+        "timecode": {
+          "type": "string",
+          "pattern": "^[0-9]{2}:[0-9]{2}:[0-9]{2}(:[0-9]{2})?$",
+          "description": "SMPTE-style HH:MM:SS or HH:MM:SS:FF timecode."
+        }
+      }
+    },
+    "provenance": {
+      "description": "The provenance record of the context that produced the run: vmafx_context_provenance_json() (RC4 WP5, #2288) carries one key per field of VmafxProvenance and its models, features and annotations. The authoritative field contract is the OpenAPI Provenance schema (api/openapi/vmafx-server-v1.yaml) and the VmafxProvenance definition in core/api/vmafx.toml; this schema pins the identity anchor so a timeline stays attributable and leaves the field contract to that single source.",
+      "type": "object",
+      "required": ["digest"],
+      "properties": {
+        "digest": {
+          "type": "string",
+          "pattern": "^sha256:[0-9a-f]{64}$",
+          "description": "The record's own digest: the digest member of VmafxProvenance, the SHA-256 of the record's canonical JSON (RFC 8785) without digest and elapsed_ns."
+        }
+      }
+    },
+    "scoring_configuration": {
+      "description": "The scoring-option surface in effect for the run (#2258, WP8): the scoring component group of api/openapi/vmafx-server-v1.yaml. The skeleton leaves the members to that single source.",
+      "type": "object"
+    },
+    "frame_score": {
+      "description": "One scored frame: its time key and the scores written for it.",
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["time"],
+      "properties": {
+        "time": {
+          "$ref": "#/$defs/time_key"
+        },
+        "scores": {
+          "type": "object",
+          "description": "Keys are feature names as the mounted models name them (for example vmaf, integer_adm2); values are that frame's numbers for the feature. A frame without scores is an empty object.",
+          "additionalProperties": {
+            "type": "number"
+          }
+        }
+      }
+    },
+    "window_statistic": {
+      "description": "One statistic computed over a window of the timeline; the range is the half-open interval the writer knows (start inclusive, end exclusive when both ends are frame indices).",
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["start", "end", "statistic", "value"],
+      "properties": {
+        "start": {
+          "$ref": "#/$defs/time_key"
+        },
+        "end": {
+          "$ref": "#/$defs/time_key"
+        },
+        "statistic": {
+          "type": "string",
+          "minLength": 1,
+          "description": "The statistic's name as the writer computes it (for example pooled, mean, worst_frame)."
+        },
+        "feature": {
+          "type": "string",
+          "minLength": 1,
+          "description": "The feature the statistic belongs to; omitted for a run-level statistic."
+        },
+        "value": {
+          "type": ["number", "string"],
+          "description": "The computed value as a JSON number; a writer spells a non-finite result as the string NaN, +Inf or -Inf, and a reader matches that spelling."
+        }
+      }
+    },
+    "event": {
+      "description": "One run event. A planted event without a time key is refused by name (#2452 acceptance).",
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["type", "time"],
+      "properties": {
+        "type": {
+          "enum": [
+            "alignment_decision",
+            "drop",
+            "repeat",
+            "freeze",
+            "switch",
+            "masked_area"
+          ],
+          "description": "alignment_decision records how streams were aligned; drop, repeat and freeze record frame-handling decisions; switch records a source or configuration switch mid-run; masked_area records a region excluded from scoring. The vocabulary grows additively under HISS-14."
+        },
+        "time": {
+          "$ref": "#/$defs/time_key"
+        },
+        "detail": {
+          "type": "object",
+          "description": "The event's facts as the writer reports them (for example the alignment offsets of an alignment_decision); the skeleton constrains nothing further."
+        }
+      }
+    }
+  }
+}
diff --git a/api/testdata/run-result-timeline/invalid-event-without-time.json b/api/testdata/run-result-timeline/invalid-event-without-time.json
new file mode 100644
index 0000000000..2f66e1f070
--- /dev/null
+++ b/api/testdata/run-result-timeline/invalid-event-without-time.json
@@ -0,0 +1,19 @@
+{
+  "schema_version": 1,
+  "provenance": {
+    "digest": "sha256:1a2b3c4d5e6f708192a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f809"
+  },
+  "frames": [
+    {
+      "time": { "frame_index": 0 },
+      "scores": { "vif": 0.95102 }
+    }
+  ],
+  "windows": [],
+  "events": [
+    {
+      "type": "drop",
+      "detail": { "reason": "duplicate pts" }
+    }
+  ]
+}
diff --git a/api/testdata/run-result-timeline/invalid-unknown-schema-version.json b/api/testdata/run-result-timeline/invalid-unknown-schema-version.json
new file mode 100644
index 0000000000..cb23f10c8b
--- /dev/null
+++ b/api/testdata/run-result-timeline/invalid-unknown-schema-version.json
@@ -0,0 +1,9 @@
+{
+  "schema_version": 2,
+  "provenance": {
+    "digest": "sha256:1a2b3c4d5e6f708192a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f809"
+  },
+  "frames": [],
+  "windows": [],
+  "events": []
+}
diff --git a/api/testdata/run-result-timeline/valid-full.json b/api/testdata/run-result-timeline/valid-full.json
new file mode 100644
index 0000000000..9fdb4e0ff1
--- /dev/null
+++ b/api/testdata/run-result-timeline/valid-full.json
@@ -0,0 +1,69 @@
+{
+  "schema_version": 1,
+  "provenance": {
+    "abi_major": 0,
+    "abi_minor": 2,
+    "abi_patch": 0,
+    "active_backend": 1,
+    "version": "v0.2.0-rc.1-3-g5c941077b",
+    "commit": "5c941077bd0f8f68d2c1430e548c902a5245a8ab8",
+    "build_id": "sha256:0f1e2d3c4b5a69788796a5b4c3d2e1f00f1e2d3c4b5a69788796a5b4c3d2e1f0",
+    "compiler": "c=gcc 15.2.1 cpp=gcc 15.2.1",
+    "backends": "cpu,cuda",
+    "simd": "avx2",
+    "device_index": 0,
+    "device_name": "cpu",
+    "device_runtime": "x86_64",
+    "n_frames": 2,
+    "digest": "sha256:1a2b3c4d5e6f708192a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f809",
+    "elapsed_ns": 240000000
+  },
+  "scoring_configuration": {
+    "model": "vmaf_v1.0.16",
+    "backend": "cpu",
+    "threads": 8
+  },
+  "frames": [
+    {
+      "time": { "frame_index": 0, "timestamp_ns": 0, "timecode": "00:00:00:00" },
+      "scores": { "integer_adm2": 0.98213, "vif": 0.95102, "motion": 8.41 }
+    },
+    {
+      "time": { "frame_index": 1, "timestamp_ns": 41708333, "timecode": "00:00:00:01" },
+      "scores": { "integer_adm2": 0.97747, "vif": 0.94855, "motion": 9.12 }
+    }
+  ],
+  "windows": [
+    {
+      "start": { "frame_index": 0 },
+      "end": { "frame_index": 2 },
+      "statistic": "pooled",
+      "feature": "integer_adm2",
+      "value": 0.9798
+    },
+    {
+      "start": { "frame_index": 0 },
+      "end": { "frame_index": 2 },
+      "statistic": "worst_frame",
+      "feature": "vif",
+      "value": 0.94855
+    }
+  ],
+  "events": [
+    {
+      "type": "alignment_decision",
+      "time": { "timecode": "00:00:00:00" },
+      "detail": { "offset_frames": 0, "method": "first-frame anchor" }
+    },
+    {
+      "type": "drop",
+      "time": { "frame_index": 1, "timestamp_ns": 41708333 },
+      "detail": { "reason": "duplicate pts" }
+    },
+    {
+      "type": "masked_area",
+      "time": { "frame_index": 0 },
+      "detail": { "region": "bottom-bar", "reason": "burned-in caption" }
+    }
+  ]
+}
diff --git a/api/testdata/run-result-timeline/valid-minimal.json b/api/testdata/run-result-timeline/valid-minimal.json
new file mode 100644
index 0000000000..1d6ad5e6fa
--- /dev/null
+++ b/api/testdata/run-result-timeline/valid-minimal.json
@@ -0,0 +1,9 @@
+{
+  "schema_version": 1,
+  "provenance": {
+    "digest": "sha256:1a2b3c4d5e6f708192a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f809"
+  },
+  "frames": [],
+  "windows": [],
+  "events": []
+}
diff --git a/changelog.d/added/run-result-timeline-schema.md b/changelog.d/added/run-result-timeline-schema.md
new file mode 100644
index 0000000000..079318ddd6
--- /dev/null
+++ b/changelog.d/added/run-result-timeline-schema.md
@@ -0,0 +1 @@
+- **The RC5 run-result timeline has a schema skeleton.** `api/run-result-timeline.schema.json` defines the versioned document that will carry one run's provenance, per-frame scores, per-window statistics and events across the CLI, the C API and the server (#2452); it evolves additively under HISS-14, and the acceptance fixtures in `api/testdata/run-result-timeline/` pin the shape in `scripts/ci/tests/test_run_result_timeline_schema.py`. The writer/reader C ABI and the byte-equal write-read-write identity check land in the follow-up PRs of the same issue.
diff --git a/docs/api/run-result-timeline.md b/docs/api/run-result-timeline.md
new file mode 100644
index 0000000000..51c61dda48
--- /dev/null
+++ b/docs/api/run-result-timeline.md
@@ -0,0 +1,60 @@
+<!-- markdownlint-disable MD013 -->
+# Run-result timeline — `api/run-result-timeline.schema.json`
+
+VMAFx plans to write one report format for a scoring run instead of letting
+alignment, fields, masks and bits-per-pixel each invent their own
+([VMAFx/vmafx#2452](https://github.com/VMAFx/vmafx/issues/2452), RC5): a
+versioned JSON document that carries the run's provenance, its per-frame
+scores, its per-window statistics and its events - alignment decisions, drops,
+repeats, freezes, switches, masked areas - each located by one time key that
+can carry a frame index, a timestamp or a timecode.
+
+[`api/run-result-timeline.schema.json`](https://github.com/VMAFx/vmafx/blob/master/api/run-result-timeline.schema.json)
+is the contract of that document, and this page is its human reference. It is
+the shape only, not the reporting code: no CLI flag, C call or server endpoint
+writes the document yet. The writer/reader C ABI and the identity checks land
+in the follow-up PRs of the same issue; the converters from the existing
+XML/JSON/CSV outputs follow them.
+
+## What the document holds
+
+| Section | Carries | Contract |
+| --- | --- | --- |
+| `schema_version` | The schema version the document was written against (`1` today) | A reader refuses an unknown version by name |
+| `provenance` | The provenance record of the context that produced the scores (`vmafx_context_provenance_json()`, RC4 WP5, #2288) | The authoritative field contract is the OpenAPI [`Provenance` schema](../../api/openapi/vmafx-server-v1.yaml) and the `VmafxProvenance` definition in [`core/api/vmafx.toml`](../../core/api/vmafx.toml); the timeline schema pins the `digest` identity anchor |
+| `scoring_configuration` | The scoring-option surface in effect (#2258, WP8) | The `scoring` component group of the same OpenAPI document is the single source |
+| `frames` | The per-frame series: a time key plus the frame's per-feature scores | The time key carries at least one of frame index, timestamp, timecode |
+| `windows` | Per-window statistics: a start, an end, the statistic's name and its value | Ranges are the half-open interval the writer knows |
+| `events` | The run's events: a type from the additive vocabulary, a required time key, optional facts | An event without a time key is refused by name |
+
+The time key mirrors what a run actually knows: a frame score carries the
+0-based display-order frame index (the stream-metadata `display_index` of
+[`api/stream-metadata-fields.json`](https://github.com/VMAFx/vmafx/blob/master/api/stream-metadata-fields.json)),
+a wall-clock event carries the nanosecond timestamp, and a writer may add the
+SMPTE-style timecode when the run has one.
+
+## Versioning
+
+The document evolves additively under the project's
+[Append-Only ABI](../principles.md) invariant (HISS-14): after a release, the
+schema gains members, and never removes, renames or retypes one. `schema_version`
+is the integer a document was written against; a reader that meets a version it
+does not know refuses the document by name rather than guessing. The acceptance
+fixtures that pin today's shape live in
+[`api/testdata/run-result-timeline/`](https://github.com/VMAFx/vmafx/tree/master/api/testdata/run-result-timeline)
+and run in
+[`scripts/ci/tests/test_run_result_timeline_schema.py`](https://github.com/VMAFx/vmafx/blob/master/scripts/ci/tests/test_run_result_timeline_schema.py)
+(the `tooling` suite):
+
+```bash
+python -m pytest scripts/ci/tests/test_run_result_timeline_schema.py -q
+```
+
+## Not in the skeleton
+
+The skeleton pins identities, not every field contract. The provenance record's
+fields and the scoring-option surface stay with their single sources (the
+OpenAPI document and `core/api/vmafx.toml`) instead of being copied here, so
+the two contracts cannot drift; the timeline schema constrains what makes a
+timeline attributable and addressable. The richer verdict and facts machinery
+of #2311 extends this schema in 1.1.
diff --git a/docs/rebase-notes.d/run-result-timeline-schema.md b/docs/rebase-notes.d/run-result-timeline-schema.md
new file mode 100644
index 0000000000..22010280eb
--- /dev/null
+++ b/docs/rebase-notes.d/run-result-timeline-schema.md
@@ -0,0 +1,17 @@
+## Run-result timeline schema skeleton (2026-11-10)
+
+New files only; nothing upstream corresponds to them, so a rebase cannot
+collide on their content. Two rebase-sensitive surfaces:
+
+- `REUSE.toml` — the contributor annotation block sits directly after the
+  first `[[annotations]]` catch-all. Other contributor pull requests (#3317
+  and later) append their blocks at the same position; a conflict resolves by
+  keeping both blocks, catch-all first and contributor blocks after it. Never
+  fold a contributor block into the catch-all: the catch-all credits
+  `2026 Lusoris`, and folding would misattribute contributor files to the
+  maintainer (the credits gate reads the file headers against `REUSE.toml`).
+- `api/run-result-timeline.schema.json` — the document evolves additively
+  under HISS-14. A rebase that removes, renames or retypes a schema member,
+  or reorders the `schema_version` contract, is a break of the additive
+  contract, not a conflict to clean up; restore the schema side and reopen
+  the discussion instead.
diff --git a/scripts/ci/tests/test_run_result_timeline_schema.py b/scripts/ci/tests/test_run_result_timeline_schema.py
new file mode 100644
index 0000000000..890706d307
--- /dev/null
+++ b/scripts/ci/tests/test_run_result_timeline_schema.py
@@ -0,0 +1,86 @@
+# Copyright 2026 luoye-cpu
+# SPDX-License-Identifier: EUPL-1.2
+"""Acceptance fixtures for api/run-result-timeline.schema.json (issue #2452).
+
+The schema is the skeleton the RC5 run-result timeline grows from; these
+fixtures pin the shape the issue's acceptance names:
+
+- the boundary document - every section present, all series empty - validates;
+- the positive document, which carries entries in every section, validates;
+- a planted event without a time key is refused by name (the refusal points at
+  the offending event);
+- an unknown schema version is refused by name (the refusal points at
+  schema_version).
+
+The byte-equal write-read-write round trip needs the writer/reader C ABI and
+lands with it in a later PR of the same issue.
+"""
+
+from __future__ import annotations
+
+import json
+import unittest
+from pathlib import Path
+from typing import Any
+
+try:
+    import jsonschema
+
+    _HAS_JSONSCHEMA = True
+except ImportError:  # the tooling-tests lock installs it; stand-alone runs may not
+    _HAS_JSONSCHEMA = False
+
+ROOT = Path(__file__).resolve().parents[3]
+SCHEMA_PATH = ROOT / "api" / "run-result-timeline.schema.json"
+FIXTURE_DIR = ROOT / "api" / "testdata" / "run-result-timeline"
+
+
+@unittest.skipUnless(_HAS_JSONSCHEMA, "jsonschema is not installed")
+class RunResultTimelineSchemaTests(unittest.TestCase):
+    """The shape rules the #2452 skeleton must hold."""
+
+    @classmethod
+    def setUpClass(cls) -> None:
+        schema = json.loads(SCHEMA_PATH.read_text(encoding="utf-8"))
+        cls.validator: Any = jsonschema.Draft202012Validator(schema)
+
+    def load(self, name: str) -> dict:
+        return json.loads((FIXTURE_DIR / name).read_text(encoding="utf-8"))
+
+    def test_valid_minimal_document(self) -> None:
+        """Boundary: every section present, all series empty."""
+        self.validator.validate(self.load("valid-minimal.json"))
+
+    def test_valid_full_document(self) -> None:
+        """Positive: provenance, scoring configuration, frames, windows, events."""
+        self.validator.validate(self.load("valid-full.json"))
+
+    def test_event_without_time_key_refused_by_name(self) -> None:
+        """A planted event without a time key is refused, naming the event."""
+        errors = list(self.validator.iter_errors(self.load("invalid-event-without-time.json")))
+        self.assertTrue(errors, "the event without a time key must be refused")
+        named = [
+            error
+            for error in errors
+            if error.json_path.startswith("$.events") and "time" in error.message
+        ]
+        self.assertTrue(
+            named,
+            "the refusal must name the offending event and its missing time key; "
+            f"got: {[error.json_path for error in errors]}",
+        )
+
+    def test_unknown_schema_version_refused_by_name(self) -> None:
+        """An unknown schema version is refused, naming the member."""
+        errors = list(self.validator.iter_errors(self.load("invalid-unknown-schema-version.json")))
+        self.assertTrue(errors, "the unknown schema version must be refused")
+        named = [error for error in errors if "schema_version" in error.json_path]
+        self.assertTrue(
+            named,
+            "the refusal must name schema_version; "
+            f"got: {[error.json_path for error in errors]}",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()