HLS integration URLs – CaptionHub

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The HLS integration output adds captions to your HLS stream by giving your player playlists that point at CaptionHub's captions. This article explains the two ways Timbra can serve those playlists, Mimic and Fixed, and which URLs you can copy from the project.

Choosing the output playlist mode

Open your project and go to the HLS integration tab. If more than one mode is available to your team, you'll see an Output playlist mode switch with a short description under it.

Mode	What it does	Use it when
Mimic	Follows the segments of your HLS stream, so each caption segment lines up with an audio segment. Needs the HLS transcription URL.	It is the default for new projects once Mimic is enabled for your team.
Fixed	Serves caption playlists in fixed two-second windows, independent of how your stream is segmented.	CaptionHub can't fetch your stream's playlists, or your stream segments awkwardly.

If you don't see the switch, your team only has Fixed mode.

Mimic

The caption playlist for each language mirrors the structure of your source audio playlist, so every audio segment has one matching caption segment. This helps with players that expect the audio and subtitle playlists to contain matching segments.

Mimic needs to know which audio playlist of your stream to follow. For an HLS stream, this is the audio track you chose for transcription. You can check or change it by selecting More actions ⋯ > Edit project and looking under Select an audio track to transcribe or Selected audio track URL. If it isn't set, the tab shows "Before using the HLS output you'll need to configure the HLS transcription URL in the settings" and no URLs.

Fixed

Fixed mode doesn't read your stream's playlists, so it works wherever CaptionHub can't fetch them. The trade-off is that caption segments don't follow your stream's segmenting, so a player that expects matching audio and subtitle segments may handle it less smoothly.

Which URL to use

The tab lists the URLs under these headings. They are available in both modes unless stated.

Use modified HLS multivariant playlist. CaptionHub's copy of your multivariant playlist with the caption tracks added. Use this if you can't change your original playlist. See Use a modified HLS multivariant playlist from CaptionHub.

Add tracks to a HLS playlist. One caption playlist URL per language, with a Default column. Copy these into your own multivariant playlist. See Integrate captions into your HLS manifest.

Replace captions in HLS multivariant playlist. Fixed mode only. It returns the modified playlist without any captions your stream already has. This is for testing only.

Changing the mode

Open the project and select the HLS integration tab.

Under Output playlist mode, choose Mimic or Fixed.

Copy the URL you need from the sections below the switch.