Interactive branched video allows users to make viewing decisions while watching, that affect the playback path of the video and potentially the outcome of the story. This type of video introduces new challenges in terms of design, for example displaying the playback progress, the structure of the branched video as well as the choices that the viewers can make. In this thesis we test three implementations of working video players with different types of playback bars: one fully viewed with no moving parts, one that zooms into the currently watched section of the video, and one that leverages a fisheye distortion. A number of usability tests are carried out using surveys complemented with observations made during the tests. Based on these user tests we concluded that the implementation with a zoomed in playback bar was the easiest to understand and that fisheye effect received mixed results, ranging from distracting and annoying to interesting and clear. With this feedback a new set of implementations was created and solutions for each component of the video player were identified. These new implementations support more general solutions for the shape of the branch segments and the position and location of the choices for upcoming branches. The new implementations have not gone through any testing, but we expect that future work can further explore this subject with the help of our code and suggestions.

Video learning material has reported benefits to in-person lectures, and it can improve knowledge transfer (Bishop & Verleger, 2013; Kim, 2013). Modern educational methods such as flipped classroom and MOOCs (MOOC, 2016) depend on implementing video as a learning resource. Furthermore, the traditional linear video has long been challenged by nonlinear video, both in terms of having interactive material (Zhang et al. 2006) and sectioned, indexed contents. In a critical approach (Bardzell, J & Bardzell, S, 2013) we investigated disadvantages to the non-linear way of using video; in particular if non-linear video streamlines the retrieval of information. We conducted an observational experiment to examine the efficiency of non-linear video compared to linear video. Results from the observation experiment conducted in this thesis, shows that the non-linear video group tended to answer less questions, within the same amount of time as the group which used the linear video. / Video påvisas förbättra kommunikationen av kunskap genom att förmedla fakta i samband med att visuellt demonstrera information i praktiken (Bishop & Verleger, 2013; Kim, 2013). Moderna pedagogiska metoder som det flippade klassrummet och MOOCs (MOOC, 2016) grundar sig att implementera video som en lärande resurs. Det traditionella linjära videoformatet har länge ifrågasatts genom icke-linjär video, både när det gäller interaktivt material men även segmenterat och indexerat innehåll (Zhang et al. 2006). Med ett kritiskt förhållningssätt (Bardzell, J & Bardzell, S, 2013) undersöker vi det icke-linjära video formatet, i synnerhet om det icke-linjära formatet påverkar effektiviteten av inlärning. Vi har utfört ett observationsexperiment för att undersöka effektiviteten av icke-linjär jämfört med linjär video. Resultaten från experimentet visar på att gruppen som använde icke-linjär video svarade på färre frågor än gruppen som använde linjär videon.

This thesis analyses how users' mouse behaviour during a video stall gets influenced by the type of video, either branched or linear, and by the presence of a playback bar. An experiment was conducted with thirty-two participants divided into six groups. Each group was watching a different combination of four videos with stalls, the first two videos belonging to the same type of video and either with or without a playback bar, and the last two videos changed in one of the two aspects. With mouse-tracking, these aspects were studied through the variables of mouse activity, average speed, average distance between the cursor and the playback bar, and the total distance moved on the screen. The participants also filled in questionnaires about their mouse behaviour, after watching each video, and their answers were later analysed through a thematic analysis. The results showed no significant differences between the groups in any of the main dependent variables. In general, within all groups, the participants moved the mouse very scarcely, indicating that the results about mouse movement should be interpreted carefully. During videos with a playback bar, mouse movements appeared to be concentrated to the stalls, focusing the movements to the bottom of the screen where the playback bar is located. Mouse behaviour during videos without a playback bar was more evenly divided between the different parts of the video and of the screen, or the user were not moving the mouse at all. Watching branched or linear videos influenced the mouse behaviour in such a way that branched videos seemed to engage the user to interact with the video player more than the linear videos. However, no difference was noticed between these conditions for active users during stalls when a playback bar was present. The thematic analysis gave clear indications that the playback bar was an important component for understanding a stall. Based on these findings, conclusions are drawn that a stall is a situation of watching videos during which mouse behaviour may be less affected by the type of video, and more influenced by the access to a playback bar. The playback bar was shown to be a source of information about the system and the situation.

Konsumtionen av video på Internet har ökat det senaste decenniet och trenden är förväntad att fortsätta stiga. Strömmande video är en ofta använd lösning för att se video på Internet. Tekniken tillåter användaren att se film medan den laddas ned. Adaptive streaming är en teknik som låter videospelaren ändra bit-raten på videon baserat på användarens tillgängliga bandbredd. En annan lösning för att göra användarens upplevelse mer skräddarsydd är ickelinjära videor. Den här typen av videor kan spelas ur sekvens. Som exempel kan en tittare välja slutet i en film eller välja vägen genom en utställning. Examensarbetet presenterar designen och implementeringen av en ny struktur för ickelinjär video. Denna struktur används av videospelaren för nedladdning och visning av adaptiv video avsedd för ickelinjära filmer, som sparas på en server. Mediaskapare kommer också att ha lättare att både visualisera och skapa filmer på ett enhetligt sätt. Det här examensarbetet presenterar i detalj de modifikationer på Adobes Open Source Media Framework och Strobe Media Playback som tillåter spelning av ickelinjära videor. Ändringarna innefattar ett användargränssnitt för ickelinjär media. Back-end implementeringarna innefattar bufferthantering för parallell nedladdning och tekniker för att hantera den nya strukturen. Slutligen presenterar det här examensarbetet proof-of-concept-tester för att styrka funktionaliteten av designen och implementeringen. Rapporten avslutas med en diskussion om framtida arbete inom fältet. / Video consumption on the Internet has been growing over the last decade and is expected to continue to increase. Video streaming is a widely used approach to viewing video on the Internet, which allows users to watch the video while it is being downloaded. Adaptive streaming is a video streaming technique that allows the player to change the downloading video’s bit rate depending on the user’s available bandwidth. Another approach to a more personal viewing experience is non-linear videos. These videos can be played in a non-sequential order. For example, a viewer can be given the choice of what ending to watch in a movie, or the path through an exhibition. This thesis will present the design and implementation of a novel structure for non-linear video. This structure is used by a video player for downloading and viewing an adaptive video intended for non-linear viewing, stored at some server. Media creators will also have an easier time to both visualize and create uniform video experiences. This thesis presents modifications to Adobe’s Open Source Media Framework and Strobe Media Playback which allow playing non-linear video. Presented in this thesis are the design and implementation details. Changes in the player include a user interface for non-linear media. The changes to the back-end include buffer management for parallel downloading and techniques to handle the new structure. Finally, this thesis presents proof-of-concept validation tests that show the functionality of the design and implementation. The thesis is concluded with a discussion of future work in this area.

Les schémas de Codage Vidéo Linéaire (CVL) inspirés de SoftCast ont émergé dans la dernière décennie comme une alternative aux schémas de codage vidéo classiques. Ces schémas de codage source-canal conjoint exploitent des résultats théoriques montrant qu’une transmission (quasi-)analogique est plus performante dans des situations de multicast que des schémas numériques lorsque les rapports signal-à-bruit des canaux (C-SNR) diffèrent d’un récepteur à l’autre. Dans ce contexte, les schémas de CVL permettent d’obtenir une qualité de vidéo décodée proportionnelle au C-SNR du récepteur.Une première contribution de cette thèse concerne l’optimisation de la matrice de précodage de canal pour une transmission de type OFDM de flux générés par un CVL lorsque les contraintes de puissance diffèrent d’un sous-canal à l’autre. Ce type de contrainte apparait en sur des canaux DSL, ou dans des dispositifs de transmission sur courant porteur en ligne (CPL). Cette thèse propose une solution optimale à ce problème de type multi-level water filling et nécessitant la solution d’un problème de type Structured Hermitian Inverse Eigenvalue. Trois algorithmes sous-optimaux de complexité réduite sont également proposés. Des nombreux résultats de simulation montrent que les algorithmes sous-optimaux ont des performances très proches de l’optimum et réduisent significativement le temps de codage. Le calcul de la matrice de précodage dans une situation de multicast est également abordé. Une seconde contribution principale consiste en la réduction de l’impact du bruit impulsif dans les CVL. Le problème de correction du bruit impulsif est formulé comme un problème d’estimation d’un vecteur creux. Un algorithme de type Fast Bayesian Matching Pursuit (FBMP) est adapté au contexte CVL. Cette approche nécessite de réserver des sous-canaux pour la correction du bruit impulsif, entrainant une diminution de la qualité vidéo en l'absence de bruit impulsif. Un modèle phénoménologique (MP) est proposé pour décrire l’erreur résiduelle après correction du bruit impulsif. Ce modèle permet de d’optimiser le nombre de sous-canaux à réserver en fonction des caractéristiques du bruit impulsif. Les résultats de simulation montrent que le schéma proposé améliore considérablement les performances lorsque le flux CVL est transmis sur un canal sujet à du bruit impulsif. / SoftCast based Linear Video Coding (LVC) schemes have been emerged in the last decade as a quasi analog joint-source-channel alternative to classical video coding schemes. Theoretical analyses have shown that analog coding is better than digital coding in a multicast scenario when the channel signal-to-noise ratios (C-SNR) differ among receivers. LVC schemes provide in such context a decoded video quality at different receivers proportional to their C-SNR.This thesis considers first the channel precoding and decoding matrix design problem for LVC schemes under a per-subchannel power constraint. Such constraint is found, e.g., on Power Line Telecommunication (PLT) channels and is similar to per-antenna power constraints in multi-antenna transmission system. An optimal design approach is proposed, involving a multi-level water filling algorithm and the solution of a structured Hermitian Inverse Eigenvalue problem. Three lower-complexity alternative suboptimal algorithms are also proposed. Extensive experiments show that the suboptimal algorithms perform closely to the optimal one and can reduce significantly the complexity. The precoding matrix design in multicast situations also has been considered.A second main contribution consists in an impulse noise mitigation approach for LVC schemes. Impulse noise identification and correction can be formulated as a sparse vector recovery problem. A Fast Bayesian Matching Pursuit (FBMP) algorithm is adapted to LVC schemes. Subchannels provisioning for impulse noise mitigation is necessary, leading to a nominal video quality decrease in absence of impulse noise. A phenomenological model (PM) is proposed to describe the impulse noise correction residual. Using the PM model, an algorithm to evaluate the optimal number of subchannels to provision is proposed. Simulation results show that the proposed algorithms significantly improve the video quality when transmitted over channels prone to impulse noise.