Track a sliding HLS window by sequence number

The useful distinctions

• MEDIA-SEQUENCE identifies the first listed media segment.
• Following segments increment that number by one.
• Removing earlier segments advances the first sequence number.

Assign identities before comparing positions

For the invented window, the listed resources have sequence numbers 42, 43, and 44. If a later observation removes the first resource, the second resource may move to line one while retaining sequence number 43. A position-based comparison would call it a new first segment; a sequence ledger correctly recognizes the retained identity. Use separate columns for sequence number, URI, and observed position.

Do not infer a publication history from filenames

The deliberately unrelated names amber, birch, and cedar demonstrate that numbering does not have to appear in a filename. A client or inspection tool that extracts identity from a trailing digit would fail this otherwise ordinary text pattern. When comparing real observations, keep playlist retrieval times and validators as well. The sequence progression explains list identity, while the retrieval evidence explains which publication snapshot was observed. Neither establishes that all referenced bytes remain available at the origin. A retention review should therefore examine the child objects separately, especially when an older parent response may remain in a cache after its first reference has moved out of the newest window. In the illustrated window, entries map to sequence values forty-two, forty-three, and forty-four. Keep that association explicit instead of assuming that an arbitrary segment filename contains the same sequence number.

Worked example · synthetic

The three segment identities are 42, 43, and 44. Removing amber.ts in a later sliding snapshot would require the first media sequence to advance to 43.

Synthetic text example; no network operation has been performed.

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:4
#EXT-X-MEDIA-SEQUENCE:42
#EXTINF:4.0,
amber.ts
#EXTINF:4.0,
birch.ts
#EXTINF:4.0,
cedar.ts

Check the interpretation

• Map numbers independently of filenames.
• Compare retained entries across snapshots.
• Do not renumber retained segments when their list position changes.