If the subject of global subtitling standards and technologies wasn’t already complicated enough for traditional linear TV broadcasting, then designing subtitle solutions for new IP streaming and on-demand video services certainly creates some extra challenges. Whether you are a content owner, a content aggregator, broadcaster or a systems architect, there are some new pieces to the subtitling puzzle.
In general terms, when we talk about multi-platform, we mean the distribution and consumption of video content on an ever-growing selection of broadcast platforms and consumer devices, including digital TV, hybrid TV, desktop PCs and the mobile/handheld sector.
The first challenge is to realize that as you progress along this list of video consumption technologies, technical standards become increasingly fuzzy. Digital TV is mature and well-defined (largely by global region). Hybrid TV mixes a standardized broadcast function with a less-defined “DTV over IP” broadband connection, whereas desktop and mobile video consumption is largely defined by Internet connectivity and supplier-specific video streaming implementations.
When planning video services, your geographic location will go a long way in determining whether subtitling becomes a necessary component in any new multi-platform system. In some countries, regulators are requiring content distributors to adhere to the same hard-of-hearing subtitling mandates on IP Internet-delivered content as for traditional broadcast TV. In other regions, the provision of single- or multiple-language subtitles on all platforms and services will enable service providers to maximize the number of potential paying customers or viewers, as is the case for public broadcasters. Operators are increasingly deploying “closed” subtitling or captioning solutions, where the viewer chooses to display subtitles rather than “open” subtitles, which are burnt onto the video signal for all to see.
The second challenge is to understand how subtitles and closed captions are transmitted as part of digital, hybrid and streaming video services. Broadly speaking, digital and hybrid TV services conform to the norms for subtitle carriage in digital TV in each geographic region. In the USA and parts of Asia, captions are transmitted as U.S.-style 608/708 closed captions. In Europe, subtitles may be in either Teletext or DVB bit-map subtitle format, while DVB subtitles are used in the rest of the world since they are image-based and, therefore, immune to region-specific character sets. There is less subtitle format standardization on the IP streaming platforms. In some cases, closed captions are carried within the digital program stream. More often, however, subtitles are stored as a separate file on streamer servers to be accessed, frame by frame as required, by the streamer client application running on the consumer device.
In an ideal world, subtitle content for digital TV, hybrid and IP streamed, would be created at the same time. In reality, though, much of the traditional broadcast content is already subtitled. Thus, the challenge becomes one of how best to repurpose the original subtitles for re-use on secondary platforms. Often, video is edited for either duration and/or adult content, or for new ad slots and, in some cases, even for video frame-rate changes. The simplest and most obvious solution (repurposing and checking the subtitle file manually against the revised video) is time-consuming, tedious and expensive.