Include spoken subtitles with programmes as a supplementary audio track
Although it is possible for receivers to produce spoken output of subtitles using text to speech software, they have no editorial control over the mixing of the spoken subtitles with other programme sounds or audio description. It is therefore difficult to avoid the spoken subtitles interfering with those other audio contents that viewers may also require in order to fully understand and enjoy the programme content.
The most effective solution from the point of the quality of output for is for the broadcaster to generate the speech and mix it with the other programme sounds and the audio description track in order to create a supplementary audio track. This also allows the broadcaster to employ real speakers rather than using artificially synthesised speech.
Directions and techniques
Mix spoken output around the other audio into a supplementary audio track
If it is possible to include a supplementary audio track with programmes, this can be used to deliver spoken subtitles, either pre-mixed into the programme audio or as a separate track timed to fit around the programme audio and able to be mixed in by the receiver. The choice of which method to use depends on the methods of mixing supplementary audio tracks available in the region (broadcast mix or receiver mix).
The essential step is for the broadcaster to create the spoken subtitles by timing their delivery to fit around the other audio tracks, such as the programme sounds and audio description. This will ensure that the different tracks do not interfere with each other and give the maximum quality for the viewer.
Use real speakers where possible, rather than synthesised speech
Having the spoken subtitles produced by actors reading the subtitles is preferable, from a quality point of view, to producing synthesised speech using text to speech software. There are, of course, cost and workflow implications so decisions may be made based on priorities such as audience size and makeup.