## 2 State of The Art
### Nonlinear Video Exploration
#### 2.1.1 Hypervideos  
Hypervideos are based on the same notion as hypertext i.e., hypertext ideas applied on a video [27] with earliest method for video branching proposed as early as 1965 [28]. [PERSON] propose a system to identify topic changes in news broadcast by searching for special characters like '\(>>\)' placed by transcribers in news transcript to segment the video and provide hyperlinks to the identified segment [29]. This idea is enhanced by [PERSON] and [PERSON] in which authors propose a modular architecture for a hypervideo system for interactive TV portal that consists of an annotation engine, hotspot identification, a metadata format and presentation engine [30]. [PERSON] et al. apply the idea of hotspots and link nodes in educational settings and extend it with the ability to link additional material such as external web pages etc. [31]. The idea of supplementary material is used by [PERSON] and [PERSON] in their study, the authors use hypervideo principle to create a personalized and interactive storytelling system which consists of a customized video player [32]. [PERSON] et al. extends the idea of storytelling by hypervideo with the use of structured metadata schemas such as RDF annotations [33], similarly RDF annotation combined with automatic entity extraction is proposed by [PERSON] and [PERSON] [34] to generate annotations for interactive TV programs. Interactivity is an important aspect of hypervideos. [PERSON] and [PERSON] [35] experimented with alternative designs to allow user to navigate a hypervideo by reference images or a line following or grid etc. [PERSON] et al. devised an approach to automatically create navigation links for hypervideo by proposing a hierarchical summary generation method to provide detail on-demand video content browsing [36]. In order to generate hierarchical summaries authors used low-level multimodal features such as color histograms and closed captions, clustering algorithms and heuristics depending on the genre of videos to segment video clips and determine the number of levels for the hierarchy and generate hyperlinks for navigation. Authors also designed a custom interface to search the collection and a specialized video player to browse the content. [PERSON] et al. use the idea of detailed on-demand in an educational setting by offering a multimedia presentation of content [37]. In their study, authorsuse the hypervideo system which offers links to more detailed information to students in the form of high definition images and supplementary text and annotation to learn surgical procedures. [PERSON] et al. [38] observed that prior hypervideo approaches were based on ad-hoc specifications and hypermedia standard such as SMIL [39] and NCL [40] are not well-suited for hypervideos. Authors propose an annotation-driven and component-based model for hypervideo inspired by other multimedia standards but more suited for hypervideos. While [PERSON] et al. [2] proposed a different approach, in their study authors propose to use an hypervideo generation approach based on SMIL [39] specification. In order to simplify the process of authoring hypervideos, [PERSON] et al. propose an authoring system to allow non-technical users to create XML based annotations for hypervideo systems [PERSON] et al. [41]. [PERSON] et al. [42] use a hypervideo system and collaborative annotation to offer dynamically generated links to consume the content of meeting recording asynchronously. While the above-mentioned approaches create hypervideo using video content, [PERSON] and [PERSON] [43] took a different approach. In their study authors use web page interaction logs with a web page to synthesize an interactive hypervideo to allow a user to visualize webpage usage. Similarly, [PERSON] et al. [9] propose a similar approach to synthesize interactive hypervideos for corporate training scenarios. In recent survey papers, [PERSON] et al. [27], [PERSON] [44] define the following as the primary aspects of all hypervideos base approaches.