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Advertising can be defined as a form of non-face-to-face communication that uses mass media to persuade the audience [1]. In the broadcasting industry, there is an advertisement market in which consumers' access rights to advertisements are traded, and viewers can use broadcasting programs for free or at very low prices due to the profits of this advertisement market. The great advantage of broadcast advertising compared to other media is that it can effectively deliver advertising messages by using video and audio. By utilizing the advantages of such broadcast advertisements, messages can be delivered without damaging the product image, and consumers' product awareness can be maintained naturally [2].

According to the survey results of the Korea Online Advertising Association, broadcast advertising was found to be the most effective medium in terms of reliability, immersion, interest, and purchase decision making. Recently, as the consumption behavior of purchasing products after comparing cost-effectiveness through acquisition of information is spreading, broadcasting advertisements are lagging behind online advertisements such as personal computers and mobile advertisements in terms of mutual compatibility and sales linkage [3].

As a result, the size of the broadcast advertising market in 2020 is estimated to be Korean Won (KRW) 3.557 trillion, a decrease of 5.7% from the previous year. In particular, the sales of terrestrial broadcast advertisements decreased by 6.4% compared to the previous year to KRW 1.16 trillion, exceeding the average rate of decline in the broadcast advertisement market (See Table 1)[4]. Such a situation is an urgent problem for broadcasters whose advertising revenue accounts for a significant portion of their sales.

As a clue to solving the problem, it can be considered that TV, which was a typical passive media medium, has evolved into a smart TV that supports application (data service) execution and Internet environment as digital broadcasting technology is introduced. With the advent of smart TV, the passive TV viewing behavior gradually changed to an active one, which means that the consumption behavior of broadcast advertisements can also be actively changed. Therefore, it can be said that the broadcasting industry, which has provided broadcasting programs for free or at low cost through advertisements, needs a growth strategy that expands the success stories of data service, which has been shown in cases such as Video On Demand (VOD) and Electronic Program Guide (EPG), to the advertisement market.

This study designed a data service that provides additional information related to advertisements to viewers for subtitle advertisements, one of the types of broadcast advertisements. Subtitle advertisements are divided into 'Soon' advertisements and Identification (ID) advertisements. Soon advertisements refer to advertisements in the form of images that are displayed when announcing the next broadcast program. ID advertisements are advertisements in the form of images that are displayed when the name of a broadcasting station is output. (See Figure 1)

Fig. 1. 
Example of subtitle advertisement for TV broadcast

Subtitle advertisements have the advantage of being cheaper than general broadcasting advertisements composed of video and audio. However, subtitle advertisements have a weakness in that they cannot contain necessary information due to the temporal constraint that the exposure time is quite short (less than 10 seconds) and the spatial constraint that the size of the subtitles does not exceed a quarter of the TV screen.

In order to overcome the temporal and spatial limitations of subtitle advertisement, this study designed a data service that provides additional information related to subtitle advertisement. Specifically, the representative advertisement types of subtitle advertisements and main additional information for each type are formally defined, and a method of transmitting the additional information using the DVB (Digital Video Broadcasting) [5] and SI (Service Information) protocol [6], an international digital broadcasting standard, was designed. In addition, based on the contents of this study, a data service prototype based on DVB-MHP (Multimedia Home Platform) [7], an international standard for data broadcasting, was developed and the effect of using this data service prototype on the effect of subtitle advertisement was analyzed for 61 university students.

This study is meaningful in that it solves the temporal and spatial constraints of subtitle advertisements by using data services and presents new possibilities for revitalizing the broadcasting advertisement market in a situation where the broadcasting advertisement market is continuously shrinking.

A typical user scenario of this data service is as follows. (1) First, the data service displays a message on the TV screen notifying that there is a data service linked to the current subtitle advertisement when the subtitle advertisement is exposed. In case of the research, the data service outputs a notice that the data service is executed when the red button on the remote control is pressed. (2) If the viewer presses the red button on the remote control within the subtitle advertisement time (up to 10 seconds), the data service is executed and the main screen is displayed. The main screen is composed of the additional information of the subtitle advertisement. The contents of the information can be designed in various ways according to the needs of broadcasters and advertisers. (3) The viewer can terminate the data service by pressing the exit button on the remote control. The data service was designed not to automatically terminate even after the time of subtitle advertisement has elapsed, thereby avoiding a negative user experience due to unintentional termination. (See Figure 2)

Fig. 2. 
Basic Usage Scenario of Data Service

Based on the study of [8], the data service’s user interface was designed so that the output screen does not exceed one-third of the TV screen and data service can be used only with the left, right and exit buttons of the remote control. This design takes into account that the main purpose of TV usage is to watch broadcasting programs, and reflects the characteristic that the remote control is generally inconvenient for data service operation. Figure 3 shows the structure of this data service user interface. Figure 3-(a) shows that the data service can be executed by pressing the red button on the remote control while the subtitle advertisement is being displayed.

Fig. 3. 
User Interface Structure

Figure 3-(b) is the main screen of data service and provides appropriate information according to the type of advertisement target (e.g. product advertisement, company promotion, etc.). Information related to data service operation is displayed in the lower right corner of the screen.

Subtitle ads have a time limit of up to 10 seconds, so the data service must efficiently show the core content according to the advertisement target. For this purpose, this study divided the types of subtitle advertisement into 'product advertisement type' and 'company promotion type' as a pilot, and defined the main information for each type as follows. Advertisers and broadcasters can expand their advertising targets by defining new types of advertisements based on this study.

2-2-1 Product Advertisement Type additional Information Definition

The advertisement target of the product advertisement type includes various products from electronic products, food and beverages, as well as travel products. In this study, the main additional information of the product advertisement type was defined as product name, manufacturer name, promotional text, price information, and the internet search keywords that can obtain detailed information. (See Figure 4)

Fig. 4. 
Product advertisement type additional information definition

2-2-2 Company Promotion Type additional Information Definition

The advertisement target of the company promotion type can be a company, a government agency, a university, or a local government, and it has the purpose of raising brand image by exposing one's own existence. In this study, major additional information of company promotion type was defined as company name, promotional text, location, contact information, and Internet search keywords. (See Figure 5)

Fig. 5. 
Company Promotion type additional information definition

Additional information of subtitle advertisement is supplied to data service using SI protocols defined by DVB, international standard for digital broadcasting. SI is a protocol defined in the form of a table for transmitting additional information related to a broadcast network, a channel, a broadcast program, etc., and defines various tables according to the purpose of the additional information. A broadcasting station or service provider can describe arbitrary information in a protocol called 'Descriptor'. Then, this descriptor can be stored in an appropriate SI table and delivered to the digital TV receiver.

Considering the limitation that the exposure time of subtitle advertisement is quite short, this study designed a method to provide data service by loading descriptors containing additional information of subtitle advertisement in EIT-P (Event Information Table-Present). EIT-P is an SI table used to transmit additional information of a currently broadcast program. It is suitable for transmitting information that needs to be time-sensitively interlocked with a broadcasting program due to the characteristic that it is repeatedly transmitted in a short period (generally within 500ms). Table 2 and Table 3 define the descriptors to contain additional information of product advertisement type and company promotion type subtitle advertisement, respectively.

In order to experimentally analyze the effect of this data service on the effect of subtitle advertisement, a prototype of data service was developed. The prototype of this data service was produced with ‘altiComposer’[9], a data service authoring tool based on the international standard MHP for data broadcasting.alti Composer supports WYSIWYG data service development and provides a function to automatically generate executable code in MHP middleware.

Using the prototype, an experiment was conducted with 61 college students. Experimental subjects were divided into two groups. Group-A consisted of 31 people, and the prototype of this data service was used when watching subtitle advertisements. Group-B consisted of 30 people and had them watch the subtitle advertisement in a typical way without data service. After watching the subtitled advertisement, a survey was conducted with the items shown in Table 4 to measure the effectiveness of the advertisement for each group. The answers to the questionnaire items were composed of a 5-point scale of ‘Likerttechniqu’, and IBM SPSS Statics was used to analyze the survey results.

The members of group-A and group-B do not overlap, and since both groups have never experienced this data service before, it can be assumed that they are mutually independent. The effectiveness of this data service was analyzed by performing the t-test, which is commonly used to analyze whether the mean of two independent groups is statistically significant.

Table 5 summarizes the analysis results of the t-test for each questionnaire item on the effectiveness of subtitle advertisements. Regarding the degree of <Understanding>, Group-A (M=4.19) answered that their understanding of subtitle advertisement content was increased in a statistically significant way compared to Group-B (M=2.13). As for the <Favorite>, Group-A (M=4.29) said that they liked the subtitle advertisement statistically significantly compared to Group-B (M=2.20). Finally, for <Engraving>, Group-A (M=4.69) answered that the content of the subtitle advertisement was impressive compared to Group-B (M=3.61) in a statistically significant way.

The above experimental results imply that viewers' interest in subtitle advertisements is not improved just by the presence of data services when subtitle advertisements are exposed. However, once the data service is used, the additional information provided by the data service improves the understanding of the advertisement target, and it can be interpreted that this understanding led to the improvement of the favorability and engraving degree. Such analysis results suggest that, in addition to notifying the existence of data services at the time of exposure of subtitle advertisements, there is a need for an element to induce viewers to execute data services.