Video Chat with Multiple Cameras

John MacCormickDickinson Collegejmac@dickinson.edu

Copyright is held by the author/owner(s).CSCW’13 Companion, Feb. 23–27, 2013, San Antonio, Texas,USA.

ACM 978-1-4503-1332-2/13/02.

AbstractThis work provides the first rigorous investigation ofmulti-camera video chat, concentrating especially on theability of a user at one end of the conversation to switchbetween multiple views at both ends of the conversation.A user study of 23 individuals and comprehensivebenchmark experiments employing up to four webcamssimultaneously demonstrate that multi-camera video chatis both desirable and feasible on consumer hardware.

Author KeywordsConsumer video chat; multiple cameras

ACM Classification KeywordsH.5.1 [Multimedia Information Systems]:Evaluation/methodology; C.4 [Performance of systems]:Design studies

IntroductionThis extended abstract analyzes the use of multiplecameras in consumer video chat applications. Figure 1demonstrates some of the possibilities enabled by theMultiCam software package described later. In each case,a laptop running Skype has two or more USB webcamsconnected, and the chat participants at both ends of theconversation are able to switch at will between individualviews of each camera or a tiled view of all simultaneously.

That is, the remote view can be altered by the localparticipant or the remote participant.

The research questions addressed by this work are:

� Is multiple-camera video chat useful and/ordesirable? Answer: Yes, for certain scenarios.

� Is remote control of the viewpoint useful and/ordesirable? Answer: In many cases, no. But aminority of users prefer remote control in at leastsome scenarios.

� Is multiple-camera video chat feasible on commodityhardware, using existing consumer chat software(e.g. Skype)? Answer: Yes, but with some caveats.

To the best of the author’s knowledge, these threequestions are novel in the context of consumer video chat.Of course, multiple cameras and remote changes ofviewpoint have been used extensively in videoconferencingand immersive telepresence systems (e.g. [1, 2, 3, 5]).However, the markedly different hardware and physicalscenarios employed by consumers using standard videochat software such as Skype mean that the use andcontrol of multiple views require re-examination in thiscontext.

The MultiCam software packageThe experiments described later employ a softwarepackage, called MultiCam, written by the authorspecifically for this research. The MultiCam software itselfis not a primary contribution of the work. No singlefeature of MultiCam is novel, but it does provide moreconvenient remote camera-switching than anypreviously-existing software plug-in for consumer videochat. MultiCam is free and open source, and theaccompanying technical report [4] describes some

interesting trade-offs relating to the design ofmultiple-camera software.

(a) (b)

(c) (d)

(e) (f)

Figure 1: Typical MultiCam usage scenarios. Webcams arehighlighted by green circles. (a) Two forward-facing cameras.(b) Forward- and rear-facing cameras. (c) Wide shot,headshot, and close-up. (d) Two cameras for whiteboarddiscussion (e) Remote tiled view of (c). (f) Remote tiled viewof (d).

ResultsExperience with MultiCamThis subsection summarizes the author’s experience withdozens of MultiCam chats (primarily social interactionswith friends and family) over several months. Theseresults are anecdotal, complementing the results of therigorous user study described in the following subsection.Figure 1(a)–(c) shows the three camera setups thatproved most useful in these conversations. Note that oneof the cameras is often picked up and directed manuallyfor some portion of the conversation. Remote participantsrarely chose to control the switching of cameras, leavingthe burden of camera-switching with the author. Butcompared with single-camera chats, in which the onlycamera must be constantly redirected to the currentregion of interest, the burden of camera managementappeared smaller for multi-camera chats. In addition,remote participants consistently reported increasedenjoyment of multi-camera chats, compared withsingle-camera chats. Finally, the MultiCam package isdownloaded hundreds of times per month at the time ofwriting, suggesting there is a reasonable level of demandfor multi-camera video chat.

User studyA user study was conducted to examine some of thebenefits and drawbacks of using multiple cameras withvideo chat, focusing especially on a comparison betweenspeaker-controlled and listener-controlledcamera-switching. The participants comprised 23individuals ranging in age from 20 to 70 (median 40),located in three continents. Participants viewed two brieflectures using the setup shown in Figure 1(d) and (f). Inone lecture, the lecturer controlled all switches betweenthe camera views (whiteboard, sofa, tiled). In the otherlecture, the participant had exclusive control over the

camera view. Figure 2 shows the participants’ level ofagreement with the statement “When the speakercontrolled the camera, the overall experience was moresatisfactory.”

Figure 2: User preferences for speaker-controlledcamera-switching vs listener-controlled camera-switching.

Clearly, there is a strong preference for the lecturercontrolling the camera view in this scenario. The mainreasons for this, elicited via open-ended questions, arethat the participants were distracted by having to changecameras and found it more difficult to concentrate on thecontent of the lecture. In addition, the lecturer cananticipate the need for a switch and thus switches at theright time.

On the other hand, a non-trivial minority (17%) ofparticipants preferred to control the view, mainly for tworeasons: (i) they enjoyed the feeling of being in control;and (ii) they could switch back to the whiteboard whendesired. Hence, it is clear that the remote switchingfunctionality does enhance the experience for a significantfraction of users.

Benchmark experimentsThe technical report [4] describes comprehensiveexperiments demonstrating the performance ofmulti-camera video chat on commodity hardware. Twotypical results are shown here. First, we see that CPUutilization and frame rate are generally acceptable whenusing up to four cameras, though with a great deal ofvariability:

Figure 3: Benchmark of CPU and frame rate with varyingnumber of cameras.

Second, we see that adding extra cameras does nottypically add latency to the video display:

Figure 4: MultiCam display latency for single and multiplecameras. Horizontal lines show the mean and vertical linesshow the standard deviation.

ConclusionThis appears to be the first study rigorously analyzingmulti-camera video chat. It provides evidence that(i) multi-camera chat is useful and desirable; (ii) remotecontrol of the viewpoint was not desired by most users inthe scenario tested, but does enhance the experience for aminority of users; (iii) multi-camera chat is feasible oncommodity hardware.

References[1] Baker, H. H., Bhatti, N., Tanguay, D., Sobel, I., Gelb,

D., Goss, M. E., MacCormick, J., Yuasa, K.,Culbertson, W. B., and Malzbender, T. Computationand performance issues in Coliseum: an immersivevideoconferencing system. In Proc. ACM Multimedia(2003), 470–479.

[2] Divorra, O., Civit, J., Zuo, F., Belt, H., Feldmann, I.,Chreer, O., Yellin, E., Ijsselsteijn, W., van Eijk, R.,Espinola, D., Hagendorf, P., Waizenneger, W., andBraspenning, R. Towards 3D-aware telepresence:Working on technologies behind the scene. In Proc.ACM CSCW: New Frontiers in Telepresence (2010).

[3] Jouppi, N. P., Iyer, S., Thomas, S., and Slayden, A.BiReality: mutually-immersive telepresence. InProc. ACM Multimedia (2004), 860–867.

[4] MacCormick, J. Video chat with multiple cameras.Tech. rep., Dickinson College, 2012. Available ashttp://arxiv.org/abs/1209.1399.

[5] Yang, Z., Wu, W., Nahrstedt, K., Kurillo, G., andBajcsy, R. ViewCast: view dissemination andmanagement for multi-party 3D tele-immersiveenvironments. In Proc. ACM Multimedia (2007),882–891.