dc: A Live Webcast Control System Tai-Ping Yu, David Wu, Ketan Mayer-Patel, and Lawrence A. Rowe Berkeley Multimedia Research Center University of California, Berkeley ftaiping, davidwu, kpatel, [email protected] erkeley.edu t the story (e.g., recorded material, ABSTRACT as needed to presen alive-remote rep ort, etc.). Another television technique Web casts can adopt techniques develop ed by television uses video e ects to combine several video sources into to obtain higher quality. Television pro duction tech- one stream (e.g., comp osition e ects), to place text on niques, however, cannot b e integrated into web cast pro- an image to describ e who or what is b eing displayed (e.g. duction without considering the fundamental di erences titling e ects), and to transition b etween streams (e.g., in the underlying infrastructure. Wehavedevelop ed a fade e ects). An interview show, for example, might dis- general web cast pro duction mo del comp osed of three playaninterviewer in one window and a remote p erson stages (i.e., sources, broadcast, and transmission) to ad- who is b eing interviewed in a second window comp os- dress these di erences. The Director's Console (dc) ited side-by-side with titles to identify the program, the isaliveweb cast pro duction application based on this participants, or the lo cation of the remote source. mo del. It utilizes a distributed service architecture, Web cast pro ducers are reluctanttointegrate conven- which adapts to varying physical infrastructures and tional broadcast television techniques into web casts for broadcast con gurations. several reasons. First, television pro duction equipment ery exp ensive. Second, the technologies and mo dels 1. INTRODUCTION is v used in broadcast television typically require manypeo- The development of IP Multicast, the Mb one To ols ple to op erate the system. Third, most broadcast tele- [11], and commercial streaming media systems (e.g., vision programs pro duce a xed data rate, single video Apple QuickTime Streaming, Cisco IP/TV, Microsoft stream with no interaction. Fourth, web casting has a Windows Media, and Real Networks) has lead to a rapid fundamentally di erent pro duction mo del than televi- growth in the use of streaming media on the Internet. sion broadcasting and the to ols and interfaces used to Several hundred liveweb casts are pro duced eachweek pro duce high qualityweb casts must re ect the underly- that are b eing viewed by tens of thousands of viewers ing infrastructure. [20]. Web casts are b ecoming an alternative to tradi- Wehave pro duced the \Berkeley Multimedia, Inter- tional television broadcasts. faces and Graphics (MIG) Seminar" web cast on the In- The television industry has develop ed manytechniques ternet Mb one since 1995. The seminar features invited to pro duce high quality video programs that can b e used lecturers who give formal presentations. The seminar to improve web casts. One technique is to switch be- takes place in a ro om equipp ed with a variety of au- tween di erent video sources. In a typical television dio/visual hardware, which is used to pro duce the web- news pro duction, several video feeds are sent to a cen- cast. Wehave used the Berkeley MIG Seminar web cast tral studio. The director selects the stream that b est as a practical exp eriment to explore the problems asso- p ortrays the content and broadcasts that stream to the ciated with web cast pro duction. audience. News broadcasts, for example, intro duce a sub ject at the anchor desk and cut to di erent sources Our web cast is comprised of two video streams and one audio stream. One video stream fo cuses on the This research was supp orted by NSF grant ANI- sp eaker, called the speaker stream, and a second stream 9907994, NSF equipmentgrantCDA-9512332, and con- fo cuses on the presentation material, called the content tributions from Fujitsu, Intel, and NEC. stream. Figure 1 shows a sample web cast from the re- mote viewer's p ersp ective. The director can switchany of several video sources into either stream. For example, when a memb er of the lo cal audience asks a question, the content stream can be switched to a view of the audience so that a remote viewer can follow the con- versation. Or, if a remote p erson asks a question, the content stream can be switched to the remote viewer and the pro jector in the classro om can b e switched from the presentation material to the remote p erson. These examples illustrate the complexityoftheweb cast con- two capture machine streams. Video sp ecial-e ects can trol problem. The director must control the pro duction b e added to the web cast by placing an e ects pro ces- viewed by the students in the classro om and, at the sor on the edge of the studio session. It takes one or same time, he must control the pro duction viewed bya more streams from the studio session, renders the ef- remote participant. fect, and sends the new stream backinto the studio ses- sion. Stored playback material (e.g., a prede ned op en- ing segment) and remote participant video are other examples of sources available in the studio session. Pro duction of a high quality web cast is a complex op eration. In a previous pap er, a Broadcast Manager application was describ ed that automated the tasks re- quired to initiate a web cast [23]. For example, the MIG Seminar web cast requires that more then ten pro cesses b e started on di erent hosts with appropriate arguments (e.g., multicast addresses and p ort numb ers, media for- Figure 1: An example MIG Seminar web cast. The left panel mats, bit-rates, and quality settings). shows a thumbnail for each stream in the session. The right The Director's Console (dc), describ ed in this pap er, panel displays selected streams with greater resolution and frame rate. is designed to control a web cast during live pro duction. It controls the web cast sources, adds e ects to these streams, and determines the nal output. Dc is imple- The MIG Seminar originates from a classro om with mented as a system of distributed pro cesses organized many audio/video sources, computer systems, and soft- with a service mo del, which adapts to di erentphysical ware pro cesses as shown in gure 2. The classro om is infrastructure and to di erent broadcast con gurations. equipp ed with several cameras (e.g., sp eaker and audi- The remainder of this pap er presents the design and ence cameras), a VCR, and a do cument camera. These implementation of dc. Section 2 describ es the web cast devices are connected to a conventional video matrix pro duction mo del. Section 3 describ es the system archi- 1 switch. Two capture machines take video from any tecture. Next, the user interface is describ ed in Section connected input device. Moreover, they can receive the 4. Section 5 describ es the implementation. Section 6 same input simultaneously. The capture machines dig- discusses our exp eriences developing and using the to ol itize the audio and video signals for transmission into and suggests future work. Section 7 describ es related two multicast sessions (i.e., one for video and one for research. And lastly, section 8 concludes the pap er. 2 audio), whichwe call the studio session. 2. WEBCAST PRODUCTION MODEL Classroom Sources Special-Effects Speaker Camera System Aweb cast di ers from traditional television on sev- Audience Camera Video and Audio t dimensions. This section describ es some Capture Machine eral imp ortan Matrix Presentation PC Switch Video Studio Broadcast of these di erences and develops a pro duction mo del Session dc Session Elmo Capture Machine for web casts. The design and implementation of dc re- VCR Stored Material ects this pro duction mo del. We b egin by examining Remote Viewer Moderated Moderator yp es and numb er of data streams that may b e in- Remote Viewer Session the t Remote Viewer Video Audio volved in a web cast. Next, the source infrastructure used in a web cast is describ ed. Finally, the receivers of a Figure 2: Infrastructure used to pro duce the MIG Seminar web cast are characterized. In each case, di erences b e- web casts. tween the web cast environmentandaconventional tele- vision broadcast environment are highlighted and used to motivate developing to ols that meet these web cast- The studio session is analogous to the routing switcher sp eci c needs. and control ro om in a conventional television studio. As Unlike a television broadcast that is limited to one in television, web cast pro duction sends all sources to video and audio stream, a web cast can b e comprised of one lo cation, the studio session. The pro ducer/director multiple video and audio streams along with asso ciated previews all sources and selects a subset of the streams hyp ertext do cuments. The numb er of streams may also that de ne the web cast. The selected streams are sent b e dynamic. For example, during the web cast for the to the broadcast session. Thus, for a viewer to see the Berkeley MIG seminar, one video stream may be ini- slides and the sp eaker, the pro ducer sets the matrix tially used when the sp eaker is presenting his material switch to the correct con guration and broadcasts the and another video stream showing the audience maybe 1 A matrix switch is a crossbar switch that can send added to the web cast during the question and answer any input to multiple outputs.