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RE: Videos - do we need both captions and transcripts?

From: John Foliot <john@foliot.ca>
Date: Mon, 6 Feb 2017 11:45:17 -0600
To: "'Michael A. Peters'" <mpeters@domblogger.net>, <w3c-wai-ig@w3.org>
Message-ID: <010601d280a0$c7ff3680$57fda380$@ca>
Michael A. Peters wrote:
> For html5 video it might be good to have examples for adding subtitles to
> the video itself rather than just as html5 track element because videos are
> often saved for stand-alone play.
> I beliebe WebVTT subtitles can be added to mkv containers (and hence
> WebM) directly with mkvmerge, I'm not sure what has to be done to get
> WebVTT into MP4 containers, it may need to be converted to another format.

Hi Michael,

Both MKV and MP4 file formats are "wrapper" formats that contain the encoded 
media (i.e. H.264 video, or AAC audio as 2 examples), and so yes, WebVTT files 
can be included in the MP4 wrapper as well. Post-production video tools 
usually will allow the inclusion of other content types as part of the export 
work-flow (for example Adobe Premier Pro). Caption, sub-title, and similar 
support files inside of those wrapper formats are usually referred to as 
"in-band", while files referenced via the track element (child element of 
Video) are referred to as "out-of-band".

In addition to the "saving for off-line use" use-case, in-band support 
materials are also pretty much the only way of ensuring that they are 
delivered over lesser bandwidth conditions (i.e. Edge or 3G for mobile), or to 
many lower-power handhelds which lack the computing power to manage multiple 
discrete downloads and syncing on the client.

Received on Monday, 6 February 2017 17:46:11 UTC

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