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Thread: detecting caption files?

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From: Tomlins Diane
Date: Thu, Jan 11 2018 8:26AM
Subject: detecting caption files?
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Hello everyone :)
Does anyone know of a tool that is able to detect whether or not a caption file exists on videos?
I know that aXe will flag that it can't find a caption file, but when I tried it on YouTube, on a video I know has no caption file, it didn't flag anything.

Thanks!

Diane R Tomlins
HCA IT&S | Digital Media
Accessibility SME

From: Beranek, Nicholas
Date: Thu, Jan 11 2018 8:40AM
Subject: Re: detecting caption files?
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I know that the axe method is to look for a <video> element and see if it has child <track> elements with a "kind" attribute of "captions". Therefore, I'm surprised it didn't detect an issue. I did a scan just now on a YouTube video with no caption and it called out "<video> elements must have captions" appropriately. Could it be the video wasn't HTML5 <video>? Or could it be that there actually was a <track kind="captions"> present but no captions were coming through on the video?

That's curious!

Nick Beranek
Capital One

-----Original Message-----
From: WebAIM-Forum [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of Tomlins Diane
Sent: Thursday, January 11, 2018 10:26 AM
To: WebAIM Discussion List < = EMAIL ADDRESS REMOVED = >
Subject: [WebAIM] detecting caption files?

Hello everyone :)
Does anyone know of a tool that is able to detect whether or not a caption file exists on videos?
I know that aXe will flag that it can't find a caption file, but when I tried it on YouTube, on a video I know has no caption file, it didn't flag anything.

Thanks!

Diane R Tomlins
HCA IT&S | Digital Media
Accessibility SME



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From: John Foliot
Date: Thu, Jan 11 2018 8:55AM
Subject: Re: detecting caption files?
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Hi Diane,

Caption files can be tricky things, because there is more than one way of
supplying them on a site: you can use the @track attribute (out of band),
OR, using the appropriate API, the captions can be delivered "in-band".

File formats such as .mp4 and .mkv are "wrapper formats" - containers for
multiple pieces of content (think similar to a .zip file - not exactly, but
a good approximation...). So, for example, an .mp4 file actually contains a
video encoded using a codec like H.264, and audio track using something
like AAC encoding, and... if created properly, the content creator can also
include other content files inside the .mp4 file, like the time-stamped
caption file (.vtt). Placing caption files 'inside' of an .mp4 file happens
at the post-production level (i.e. the video creation tool/suite).

I can double check with Deque's engineers if aXe is programmed to examine
'inside' of MP4 files looking for a caption file, and if so, how, but I
also recall that YouTube also uses a proprietary time-stamp format for
their captions, so if aXe is only looking for WebVTT or TTML
markup/time-stamp formats, it *might* be missing the proprietary format.
(Just a guess at this time).

For testing purposes today, I would recommend you continue with manual
tests: nother requirement is that the end-user can toggle the captions on
or off (when provided as closed captions), and that control/button needs to
also work from the keyboard only, so traditionally when I am testing a
video region/player, I do all the tests (manual and mechanical) at one
time, so, can you toggle captions on or off via the keyboard only will also
determine whether captions exist or not ;)

HTH

JF

On Thu, Jan 11, 2018 at 9:26 AM, Tomlins Diane <
= EMAIL ADDRESS REMOVED = > wrote:

> Hello everyone :)
> Does anyone know of a tool that is able to detect whether or not a caption
> file exists on videos?
> I know that aXe will flag that it can't find a caption file, but when I
> tried it on YouTube, on a video I know has no caption file, it didn't flag
> anything.
>
> Thanks!
>
> Diane R Tomlins
> HCA IT&S | Digital Media
> Accessibility SME
>
>
>
> > > > >



--
John Foliot
Principal Accessibility Strategist
Deque Systems Inc.
= EMAIL ADDRESS REMOVED =

Advancing the mission of digital accessibility and inclusion

From: Tomlins Diane
Date: Thu, Jan 11 2018 10:19AM
Subject: Re: detecting caption files?
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Nick,
I know for a fact that the video I was looking at has no caption file of any kind, and we all know that YT's auto-captioning is not that great.
I'm wondering if aXe called out the missing caption when the video was iframed into our page vs. looking at that same video out on YT when it did not flag it as missing the caption file.


>I know that the axe method is to look for a <video> element and see if it has child <track> elements with a "kind" attribute of "captions". >Therefore, I'm surprised it didn't detect an issue. I did a scan just now on a YouTube video with no caption and it called out "<video> elements >must have captions" appropriately. Could it be the video wasn't HTML5 <video>? Or could it be that there actually was a <track [Diane Tomlins] >kind="captions"> present but no captions were coming through on the video?

Nick Beranek

Capital One

From: Tomlins Diane
Date: Thu, Jan 11 2018 10:27AM
Subject: Re: detecting caption files?
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Thanks John :)
It would be nice if there was something that could detect the presence of caption files, but I understand that could be really difficult with the different formats. I can pretty much tell if the caption I see is YT's version, or an actual added caption file. It's especially obvious when you've got medical terminology or doctors with heavy accents, what comes out of YT's auto-captioning is hilarious (almost).

>I can double check with Deque's engineers if aXe is programmed to examine 'inside' of MP4 files looking for a caption file, and if so, how, but I >also recall that YouTube also uses a proprietary time-stamp format for their captions, so if aXe is only looking for WebVTT or TTML >markup/time-stamp formats, it *might* be missing the proprietary format.
>(Just a guess at this time).


JF

From: Jonathan Avila
Date: Fri, Jan 12 2018 8:45AM
Subject: Re: detecting caption files?
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> >I can double check with Deque's engineers if aXe is programmed to examine 'inside' of MP4 files looking for a caption file, and if so, how, but I >also recall that YouTube also uses a proprietary time-stamp format for their captions, so if aXe is only looking for WebVTT or TTML >markup/time-stamp formats, it *might* be missing the proprietary format.
>(Just a guess at this time).

In my experience aXe core fails youtube videos for missing track elements even when the videos have captions. This is a situation where flagging a missing caption track is a potential violation that must be reviewed by a human or better automation is needed to inspect the encapsulated file or other new techniques need to be researched.

Jonathan

-----Original Message-----
From: WebAIM-Forum [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of Tomlins Diane
Sent: Thursday, January 11, 2018 12:27 PM
To: WebAIM Discussion List < = EMAIL ADDRESS REMOVED = >
Subject: Re: [WebAIM] detecting caption files?

Thanks John :)
It would be nice if there was something that could detect the presence of caption files, but I understand that could be really difficult with the different formats. I can pretty much tell if the caption I see is YT's version, or an actual added caption file. It's especially obvious when you've got medical terminology or doctors with heavy accents, what comes out of YT's auto-captioning is hilarious (almost).

>I can double check with Deque's engineers if aXe is programmed to examine 'inside' of MP4 files looking for a caption file, and if so, how, but I >also recall that YouTube also uses a proprietary time-stamp format for their captions, so if aXe is only looking for WebVTT or TTML >markup/time-stamp formats, it *might* be missing the proprietary format.
>(Just a guess at this time).


JF