Slideshow allows broadcasters enhance digital radio broadcasts with visuals using standard image formats and common publishing tools. Anything that can be coded as a JPEG or PNG can be broadcast over DAB and accurately triggered to appear in time with the audio.
Slideshow is defined as a hybrid digital radio application in ETSI TS 101 499. It can be transported in broadcast or streaming services, with meta-data to support click-through URLs and categorisation. It is commonly supported in transmission equipment and receivers.
Slideshow is transmitted in either X-PAD (where data capacity is allocated within an existing audio stream) or packet mode (where data capacity is allocated in a separate channel on the multiplex, so that it can be shared between several services), and can be effective at data rates from well under 1kbit/s upwards. Slides are 320x240pix in size and are shown at an interval between 10-30sec per image. Optional features include animation via the PNG format and ‘Categorised Slideshow’ which provides for caching and browsing images by category.
Slides can be compiled manually or through an automated process, drawing from existing digital assets such as news, presenter information, artist images, weather, travel, promotional items and of course advertising information. The slide image can be encoded using JPEG (which typically favors photographic content) or PNG (which favors text content). Optional metadata provides for control of presentation timing of slide images via a trigger time.
A wide range of multimedia receivers for home and automotive use support slideshow, which is an attractive enhancement to audio programmes with its wide variety of complementary information. Essential for in-vehicle reception is the aspect of driver distraction which conflicts with flashy or attention-seeking presentations. A slide interval of 10-30 secs has proven useful and attractive.