Minor errors in WGBH guidelines for accessible (talking) DVD/STB menus

Where to find the original

Read WGBH’s “Developer’s Guide to Creating Talking Menus for Set-Top Boxes and DVDs.”

Errors and comments

Network IDs

How to identify a channel or network in a voice prompt:

The talking menu begins reading, channel by channel, and Joe hears the following:

“10 p.m.” (brief pause)

“Channel 2. CNN: Larry King Live.”

“Channel 3. Fox Baseball: Red Sox vs. Yankees.”

“Channel 4...,” etc.

I assume this means Channel 3. Fox. Baseball: Red Sox vs. Yankees. The network has to be identified.

Also, “..., etc.” is a dodge. Give us more examples. Don’t skimp.

Verbose vs. terse

Repeat the navigation instructions as often as seems appropriate for the expected use pattern. For example, a DVD that someone might pick up only occasionally should frequently remind the user of what he or she needs to do next. An STB that will be used more often might have both a wordy option, with frequent reminders of how to use it, and a more terse option for those who are familiar with it.

Exactly which mechanism does WGBH suggest authors use to program “a wordy option” and “a more terse option”? Explain how it could be done today.

Degree of visual impairment

The guidelines never get their story straight about the degree of visual impairment of users of audio navigation. GBH would have been better off with a separate section that stated something like “People who have no or little usable vision, people with quite a bit of usable vision, and people with no vision problems will all use audiovisual navigation. You need to take this disparity in visual impairment into account in some cases” The improved guidelines could then explain what those cases are and how in detail to deal with them.

Remember that many users will listen to the audio navigation while looking at the visual menus.

But by the same token, if a sighted user cannot disable the system, it might be seen as a liability, despite the fact that many sighted users can derive benefit from an audio-navigation feature.

Small-scale usability testing suggests that sighted users will benefit from having talking menus on by default. However, until audio navigation is a more-widely-accepted feature, the default setting will in most cases leave the talking menu disabled.

Which sighted users benefit from talking menus? Learning-disabled people, presumably, but also nondisabled people who are curious? Developers? Tinkerers? Who?

Silent buffers

The guidelines mention “silent buffer handles”:

Are there buffering concerns that require silent pads to be added to individual audio clips?

Include short, silent buffer handles at the beginning and end of individual speech files, if necessary. These handles ensure that the spoken item will not be truncated when played for the user. It is important, however, to fine-tune these handles to keep them as brief as possible to make the system as responsive as possible.

Apparently many DVD players experience a delay in playback of audio clips due to buffering speed. This delay can cause the head and even the tail of the clip to become truncated.... The length of the silent clip should be determined empirically, as the optimum length depends upon size of the clip and the horsepower of the DVD player, which varies among different models. To begin, a developer might try adding 15 to 20 frames (0.5 to 0.75 seconds) to the head and tail of the clip.

The guidelines don’t tell you:

how to add these buffers (concatenate the silent frames to a recorded segment? have the narrator pause after recording starts and before it ends?)
if any particular kinds of voice segments don’t need them
how to test for the latency that the buffers are supposed to prevent (just that you ought to test them)

Overbroad definition of set-top box

A set-top box, or STB, refers to any device inserted between the cable or satellite feed and the user’s television set. These devices have the capability to select and display individual channels.

A small number of people still use external caption decoders, which would be “set-top boxes” under this definition, yet not all of them “select and display individual channels.” (My old TeleCaption II did.)

DVB standard

Given the flexibility of the DVB standard, one would expect that adding an audio-navigation capability to an STB would be simple matter of writing the proper software to include in the STB’s operating system.

The guidelines could have told us how and why the DVB spec is so flexible, and which features would have led one to believe that adding audio navigation would be simple.