Media Accessibility User Requirements - review comments

Dear PFWG,

Please see the following review comments from the BBC on the MAUR document


General comment: the writers may wish to consider this user experience
good practices document drafted by BBC:
General comment: The BBC would like to commend the activity of creating
this very useful document.

Section 3.6 Captioning

[CC-10] Render a background in a range of colors, supporting a full range
of opacity levels.

Comment: It enhances readability if the bounding box of the background
area is not tightly aligned with the text edges, i.e. that some background
space is visible especially at each end of a line area, for example the
equivalent of the width of half a space in the selected font.

Proposal: Add a new requirement:-

"Enable the bounding box of the background area to be extended by a
present distance relative to the foreground text contained within that
background area."

[CC-11] Render text in a range of colors.
The user should have final control over rendering styles like color and
fonts; e.g., through user preferences.

Comment: A default palette of colours suitable for colour blind users
should be available to distinguish editorial concepts, such as speakers.
There are likely to be conflicting requirements between different users
with differing cognitive conditions to maximise the accessibility of
content, so full colour customisation should be available. For example
users with cognitive conditions such as dyslexia (itself an umbrella label
for a variety of conditions), ADHD and Asperger's may find that viewing
content that is given a particular colour cast, akin to viewing through
blue spectacles, say, helps them to read presented text. Whilst further
research is needed in this area, we should recommend that full colour
customisation is available.

[CC-12] Enable rendering of text with a thicker outline or a drop shadow
to allow for better contrast with the background.

Comment: It's correct that this should be enabled however it should not be
presented as a suitable general alternative to displaying text on a
non-transparent background, from a legibility perspective. For example,
white text with drop shadows on a transparent background is not readable
over a white video, such as footage of snow.

Comment: The use of drop shadows increases the sense of 'busyness' that
can have negative impacts for viewers with some cognitive conditions.
In general it is preferable not to use drop shadows for the purpose of
improving text legibility.

[CC-13] Where a background is used, it is preferable to keep the caption
background visible even in times where no text is displayed, such that it
minimizes distraction. However, where captions are infrequent the
background should be allowed to disappear to enable the user to see as
much of the underlying video as possible.

Comment: this is a cultural/editorial feature that is not accepted
globally and is likely to result in unnecessarily obscured video.

Proposal 1: Remove this requirement.

Proposal 2 (in case Proposal 1 is rejected): Change 'it is preferable' to
'it should be possible'.

[CC-14] Allow the use of mixed display styles‹ e.g., mixing paint-on
captions with pop-on captions‹ within a single caption cue or in the
caption stream as a whole. Pop-on captions are usually one or two lines of
captions that appear on screen and remain visible for one to several
seconds before they disappear. Paint-on captions are individual characters
that are "painted on" from left to right, not popped onto the screen all
at once, and usually are verbatim. Another often-used caption style in
live captioning is roll-up - here, cue text follows double chevrons
("greater than" symbols), and are used to indicate different speaker
identifications. Each sentence "rolls up" to about three lines. The top
line of the three disappears as a new bottom line is added, allowing the
continuous rolling up of new lines of captions.

Proposal: Add a Note to this section:

"The comprehension and appreciation of captions and subtitles depends on
how well matched they are to the related video content, editorially. In
particular the pacing of the content should be reflected in the caption
text; for example a fast paced drama or is likely to benefit from
relatively short captions that change more often in comparison to a slow
paced one. In extremis very fast changing short subtitles do cause
readability problems because they can prevent viewers from having enough
attention to consider the video; such extremes should be avoided."

Proposal: Add a Note to this section:
"When displaying captions in the paint-on style care should be taken to
ensure that the final words that are displayed are visible for enough time
that they can be read."


[CC-15] Support positioning such that the lowest line of captions appears
at least 1/12 of the total screen height above the bottom of the screen,
when rendered as text in a right-to-left or left-to-right language.

Comment: this rule is not global and, in the measurement of 1/12 appears
to be arbitrary. We agree that a gap does help readability, but propose
that the specific distance requirement should be removed.

Comment: The legibility of rendered text depends on the size of the text
as perceived by the viewer, which is in turn dependent on the display size
and the distance between display and viewer. I propose adding:

Proposal: Add a new requirement:-
"Enable responsive choice of text size based on display size and expected
distance between display and viewer."


Comment: To maximise readability of text it is often beneficial to use a
font that is optimised for the technology used within the platform and
display. For example the approach to handling multiple screen sizes in
Android means that unmodified general purpose fonts such as Helvetica do
not always render well - in that case the Roboto font may be preferable.

Proposal: Add a new requirement:-
"Enable fonts optimised for readability on the display in use to be
preferred where they are available."

Section 4.7 Requirements on the use of the viewport


[VP-5] Captions and subtitles traditionally occupy the lower third of the
video, where controls are also usually rendered. The user agent must avoid
overlapping of overlay content and controls on media resources. This must
also happen if, for example, the controls are only visible on demand.


If there are several types of overlapping overlays, the controls should
stay on the bottom edge of the viewport and the others should be moved
above this area, all stacked above each other.

Comment: It is also important to avoid captions and subtitles overlapping
editorially important content areas such as mouths, burned in text etc.

Comment: We strongly disagree with the stacking approach described in the
Note. In many cases the best location for the captions/subtitles in this
scenario is towards the top of the viewport, where it is less likely to
obscure mouths etc.

Proposal: Remove or edit the note to reflect these comments, for example
resulting in:

"If there are several types of overlapping overlays, they should be
positioned as far as possible to avoid obscuring editorially important
parts of the underlying video such as burned in text, mouths etc. Users
typically expect controls to appear at the bottom of the viewport.
Controls should not be prevented from becoming usable due to


Kind regards,

Nigel Megitt

Nigel Megitt
Lead Technologist, BBC Technology, Distribution & Archives
BC4 A3 Broadcast Centre, Media Village, 201 Wood Lane, London W12 7TP

Received on Thursday, 4 December 2014 15:00:04 UTC