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Re: [sdw] WebVMT: Investigate better out-of-band link handling (#1107)

From: François Daoust via GitHub <sysbot+gh@w3.org>
Date: Tue, 08 Jan 2019 14:18:22 +0000
To: public-sdwig@w3.org
Message-ID: <issue_comment.created-452313783-1546957100-sysbot+gh@w3.org>
In the WebVMT case, my working assumption is that the main starting point is either the HTML page (`HTML -> media, VMT`) or the media file (`media -> VMT`). Use cases that start from the VMT file seem less likely to me. That may be where we have different perspectives.

> Firstly, warnings could be displayed by the WebVMT engine in the rendered webpage, e.g. by displaying text in the map element instead of the rendered map. Is there a precedent for displaying errors or warnings within the browser, e.g. broken image link?

Sure, that's typically the kind of information that you get on the developer console when you browse a page. However, that information is always restricted to resources that the browser needs to fetch to render the page. If it already has the URL of the media file and of the WebVMT file, the WebVMT engine does not need to fetch the link between the VMT file and the media file to render things. That would take extra time, CPU and network usage. So I wouldn't expect it to report on it being broken.

> Secondly, to clarify my webpage-image analogy, the VMT file contains a URL to the media file in the same way as an HTML file contains a URL to the image file. I can't see a bidirectional link - there's no link from the VMT to the HTML. Have I misunderstood?

The analogy does not work at 100% because there may be 3 resources at play in your case (HTML, media, VMT). In the webpage-image analogy, the main starting point for most use cases is the HTML page, so link is `HTML -> image`.

> While the HTML use case is important for WebVMT, it's not the only use case. The VMT file should contain sufficient data for all use cases, and the purpose of the WebVMT media block is to identify the linked media - particularly in non-HTML use cases, e.g. for the mobile demo. In the HTML use case, some of the data can be duplicated into the HTML file, which is a product of the VMT source data, e.g. by a PHP script.

In the demo you link to, I wouldn't expect users to point the player at the VMT file directly, in the same way as I wouldn't expect users to point a video player at a subtitles file directly (that is, it may work, but I wouldn't expect the video to appear as if by magic).

> If the linked media URL is not in the VMT file, where would that information be recorded?

I don't know. How is the link between a video file and a subtitles file recorded?
I'd record it as metadata in the video file (again because that's the starting point for me)

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Please view or discuss this issue at https://github.com/w3c/sdw/issues/1107#issuecomment-452313783 using your GitHub account
Received on Tuesday, 8 January 2019 14:18:28 UTC

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