When to use

• After generating your outputs (interval instructions, masks, etc.), before submission/hand-off.

Checks

• Key format: every key is

  "{start}->{end}"

  , integers only,

  start<=end

  .
• Coverage: max frame index ≤ video total-1; consistent with your sampling policy.
• Frame count: NPZ

  f_{i}_*

  count equals sampled frame count; no gaps or missing components.
• CSR integrity: each frame has

  data/indices/indptr

  ;

  len(indptr)==H+1

  ;

  indptr[-1]==indices.size

  ; indices within

  [0,W)

  .
• Value validity: JSON values are non-empty string lists; labels in the allowed set.

Reference snippet

import json, numpy as np, cv2
VIDEO_PATH = "<path/to/video>"
INSTRUCTIONS_PATH = "<path/to/interval_instructions.json>"
MASKS_PATH = "<path/to/masks.npz>"
cap=cv2.VideoCapture(VIDEO_PATH)
n=int(cap.get(cv2.CAP_PROP_FRAME_COUNT)); H=int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT)); W=int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
j=json.load(open(INSTRUCTIONS_PATH))
npz=np.load(MASKS_PATH)
for k,v in j.items():
    s,e=k.split("->"); assert s.isdigit() and e.isdigit()
    s=int(s); e=int(e); assert 0<=s<=e<n
    for lbl in v: assert isinstance(lbl,str)
frames=0
while f"f_{frames}_data" in npz: frames+=1
assert frames>0
assert npz["shape"][0]==H and npz["shape"][1]==W
indptr=npz["f_0_indptr"]; indices=npz["f_0_indices"]
assert indptr.shape[0]==H+1 and indptr[-1]==indices.size
assert indices.size==0 or (indices.min()>=0 and indices.max()<W)

Self-check list

• JSON keys/values pass format checks.
• Max frame index within video range and near sampled max.
• NPZ frame count matches sampling; keys consecutive.
• CSR structure and

  shape

  validated.