FA-11271 / Media timeline seeking / Open access
Clip concatenation offset by duration · case 01
Concatenated clips restart their timestamps at zero and overlap earlier clips.
ROOT CAUSE
Concatenated clips restart their timestamps at zero and overlap earlier clips.
VERIFIED REPAIR
Preserve the media contract: Clips are [duration,local timestamped frames], with nonnegative durations and local timestamps inside each clip. Concatenate timelines using full declared clip durations.
Unsuccessful approach: Adding clip index uses item count instead of elapsed media duration.
Case contract
Clips are [duration,local timestamped frames], with nonnegative durations and local timestamps inside each clip. Concatenate timelines using full declared clip durations.
Why this case matters
A deterministic local media controller stage; metadata and downloaded data are supplied explicitly. No external player, service or codec is required.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(clips):
return [[t,value] for duration,frames in clips for t,value in frames]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([[5, [[0, 'a'], [3, 'b']]], [4, [[0, 'c'], [2, 'd']]]],)),[[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']])
check('fixture 2',solve(*([],)),[])
check('fixture 3',solve(*([[2, [[0, 'a']]]],)),[[0, 'a']])
check('fixture 4',solve(*([[0, []], [3, [[1, 'x']]]],)),[[1, 'x']])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| fixture 1 | [[0, 'a'], [3, 'b'], [0, 'c'], [2, 'd']] | [[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']] | Failed |
| fixture 2 | [] | [] | Passed |
| fixture 3 | [[0, 'a']] | [[0, 'a']] | Passed |
| fixture 4 | [[1, 'x']] | [[1, 'x']] | Passed |
SHA-256 / b9c7ff64572c17011e2e7bca04868c0ffd9b405649814fc972e3dcf0f4175c93
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(clips):
return [[t+i,value] for i,(duration,frames) in enumerate(clips) for t,value in frames]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([[5, [[0, 'a'], [3, 'b']]], [4, [[0, 'c'], [2, 'd']]]],)),[[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']])
check('fixture 2',solve(*([],)),[])
check('fixture 3',solve(*([[2, [[0, 'a']]]],)),[[0, 'a']])
check('fixture 4',solve(*([[0, []], [3, [[1, 'x']]]],)),[[1, 'x']])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| fixture 1 | [[0, 'a'], [3, 'b'], [1, 'c'], [3, 'd']] | [[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']] | Failed |
| fixture 2 | [] | [] | Passed |
| fixture 3 | [[0, 'a']] | [[0, 'a']] | Passed |
| fixture 4 | [[2, 'x']] | [[1, 'x']] | Failed |
SHA-256 / a31c8073173e5afebf895d2756f33564e21c4a7a3d7a0dd0a5b6a0f024342ac2
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(clips):
return [[t+sum(x[0] for x in clips[:i]),value] for i,(duration,frames) in enumerate(clips) for t,value in frames]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([[5, [[0, 'a'], [3, 'b']]], [4, [[0, 'c'], [2, 'd']]]],)),[[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']])
check('fixture 2',solve(*([],)),[])
check('fixture 3',solve(*([[2, [[0, 'a']]]],)),[[0, 'a']])
check('fixture 4',solve(*([[0, []], [3, [[1, 'x']]]],)),[[1, 'x']])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| fixture 1 | [[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']] | [[0, 'a'], [3, 'b'], [5, 'c'], [7, 'd']] | Passed |
| fixture 2 | [] | [] | Passed |
| fixture 3 | [[0, 'a']] | [[0, 'a']] | Passed |
| fixture 4 | [[1, 'x']] | [[1, 'x']] | Passed |
SHA-256 / 84771b9d0966229df334ebce73282d838c15798fb95be66e657a16cf1220ef9b
Verification & scope
This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:38:46.459546+00:00.
Case digest / ab2aca224b8068c677e5b798eb537d74691c8fb2751b9ebdd595714918cc7523