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Private Media Session, Cache, and Timed Text

Last updated: 4 Oct 20268 min read
tutorial
IntermediateBy AITrove Editorial

A private clip is rarely one object. It may have a poster, several renditions, a manifest, many segments, caption tracks, and a transcript. Every object can reveal case information, so the authorization inventory must cover each route. A public CDN cache key cannot safely ignore user or grant scope for private material. Conversely, a narrowly scoped signed path can support efficient delivery if expiry, leakage, and revocation behavior are explicit. Timed text is part of the media revision; captions that describe an older cut can mislead a reviewer just as a mismatched video segment can.

Working case

Case 47 contains an inspection recording with captions at revision 29. After editing, the video becomes revision 30, but the old caption file remains cached at a stable address. Reviewer 63 sees words at the wrong moments and interprets a repair as unfinished. Meanwhile, a shared cache serves a poster from a private case to a different account. The fix assigns a versioned identity to video, poster, caption, and transcript together, then checks the viewer’s case permission before issuing a delivery grant. A new revision gets new cache keys. The UI exposes the caption language and transcript revision instead of silently mixing old text with new frames.

Implementation boundary

javascript
function sameMediaRevision(manifest) {
  return [manifest.poster, manifest.captions, manifest.transcript].every(
    asset => asset.revision === manifest.video.revision
  );
}
console.log(sameMediaRevision({ video: { revision: 30 }, poster: { revision: 30 }, captions: { revision: 29 }, transcript: { revision: 30 } }));
// Output: false

Create a manifest record that lists the current clip revision and every derived asset ID. When publishing a new cut, validate caption cue timing, language labels, transcript content, and poster against that cut before making it current. Deliver private assets through an authorization check or a short-lived grant bound to one asset family and requester context. Decide whether grant revocation must take effect immediately or at expiry, and do not claim stronger revocation than the delivery path provides. Put no private filenames or case text in public cache keys or response headers. Choose cache directives separately for public and private assets, and test the CDN with two accounts. Offer captions and a text transcript without forcing a video download; a caption file alone does not describe important visual information that has no speech.

Cost and boundaries

Each rendition, caption language, poster, and transcript adds storage proportional to its own bytes. Revisioned names reduce mixed-cache risk but leave old objects that need a retention and cleanup policy. Checking authorization for every small segment increases origin traffic; scoped grants can reduce that cost while introducing an expiry window. Caption validation is O(C) for C cues, with checks for ordering, overlaps under the chosen policy, and duration bounds. Track private cache misses, denied asset requests, stale revision reports, caption selection, and transcript usage. Avoid collecting exact viewing positions in routine analytics unless the product has a clear need and retention rule.

Failure trace

Request the clip manifest as an unauthorized account, then request a guessed segment, poster, caption, and transcript address; all must follow the same private policy. Change video revision while leaving an old caption path in a cache and confirm the new manifest cannot reference it. Expire a grant midway through playback and show a clear renewal or denial state without silently exposing future segments. Revoke case access and measure the maximum remaining grant lifetime. Serve malformed timed text and avoid presenting it as a correct caption. Compare transcript content with the edited cut, including relevant non-speech visual events. Test cache behavior across two tenants that happen to use similar case IDs.

Verification

  • Every derived asset follows the case access policy.
  • Video and timed text publish under one revision.
  • Cache and grant behavior is tested across accounts.

Practice drill

Publish a private 7-minute clip for case 47 with two renditions, a poster, English captions, and a descriptive transcript at revision 29. Edit the recording to revision 30 and intentionally leave one old caption file. The publish gate should refuse the mismatched asset family. Issue a 63-second delivery grant, switch accounts, and attempt direct requests for all five asset types. Review which bytes remain reachable after access revocation and document the grant window honestly. Test a text-only route that opens the transcript without a media request.

Decision note

A private media experience is a versioned family of assets with one explicit access rule, not an isolated video URL.

Common Mistakes

  • Guarding the video while leaving captions public.
  • Reusing a stable private asset URL across revisions.
  • Claiming immediate revocation for an unexpired independent grant.

Related lessons

On-Demand Media Playback and Delivery; Media Player Source and Load State; Media Byte Ranges, Seeking, and Version Identity; Adaptive Media Buffer and Fallback Policy; Accessible Content and Media; File Ingestion and Private Asset Lifecycle.

Connected practice

Build Project: private inspection clip playback and review Web Development: media playback decisions quiz.

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