bbc
Add support for Dash.js rendered subtitles
📺 What
Extends subtitle functionality by adding the ability to use Dash.js rendered subtitles if declared in an MPD rather than using the existing side-chain.
Allows the rendering of subtitles delivered in fragmented chunks, as used for low-latency playback.
It does not implement the current customisation options that are available in the existing side-chain as Dash.js provides no interface to access the customisation options present in the BBC fork of imscJS.
A currently open PR imscJS #257 would enable customisation on upstream imscJS and work on Dash.js (imscJS Styling would allow this functionality to be added retrospectively.
🛠 How
By setting a new override - dashSubtitles, the side-chain is replaced by a new dashsubtitles object which enables text tracks in the MSE player
✅ Testing [Semi-optional]
Tests have been added to cover changes to the subtitle selector. In addition, coverage of the new dashsubtitles.js object is provided.
| Test engineer sign off | :x: |
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♿ Accessibility [optional]
Provides optional subtitles when using low-latency playback through Bigscreen player without modifications to the existing side-chain rendering.
Just a thought on naming. I wonder if embeddedSubtitles might be a little clearer. Although it does work, as subtitles are in the dash manifest, the current side-loading of subs still happens during DASH playback.
Just a thought on naming. I wonder if
embeddedSubtitlesmight be a little clearer. Although it does work, as subtitles are in the dash manifest, the current side-loading of subs still happens during DASH playback.
That makes sense, I'll adjust the naming to reflect this
References to Dash.js subtitles have now been updated to Embedded subtitles
I've submitted a PR to bbc/dash.js #95 to use bbc/imsc.js in bbc/dash.js and expose the customisation options through the dash.js settings interface. This PR could be further expanded to provide subtitle customisation to match the current offering via the side-chain. Alternatively, this work could be done in a seperate PR.