Real Time: Audio and Video

• Philipp Hoschka
• W3C Technical Staff
• Advisory Commitee Meeting / June 10, 1996

History

• January 1st: W3C starts real-time activity at INRIA
• January 15: IETF makes RTP proposed standard
• February: Netscape announces LiveMedia based on RTP
• March: Microsoft announces RTP support
• Currently: both beta versions have extended support for audio/video

Current Activity Goals

• Allow to build web-based multimedia presentations
• Allow hyperlinks into audio/video
• Interoperable solutions required !
• Use IETF's work on real-time for Web, e.g. multicast

Building Web-Based Multimedia Presentations

• Controling audio/video display
• Time representation and media synchronization

Controling Audio/Video Display

• Audio
  • Volume
  • Special effects (fade in/out), ...
• Video
  • Size
  • Last frame: disappear or freeze, ...
• Control
  • Loop n times/infinitely, Autostart
  • Control panel, Which buttons ?, ...

Current Approaches

• Netscape: <embed> tag
  • Specific attributed defined for each plugin
  • Example: <embed src=x.avi autostart=TRUE loop=true>
• W3C: <object> tag
  • geared towards requirements of applets
  • No predefined parameters for audio/video
  • Add: Attributes specific to audio/video media

Multimedia Presentations on Web

• Current
  • Rely on helper and propriatary format
  • Come from single server
• Web-based
  • Distributed storage of monomedia sources
  • Combine existing content to new content

Requirements

• Describe media synchronization
  • MHEG, HyTime, JavaScript, Java, ...
• Deal with to network problems (hard !)
  • Synchronization via RTP
  • Error resilience via ALF

Real Time Transport Protocol

• Generic headers and control messages for real-time applications
• IETF "Proposed Standards": RFC 1889/1890
• Netscape, Microsoft and many others announced support

Audio/Video Hyperlinks

• URL's for linking into audio and video files
• Adressing streaming audio/video resources via URL's
• Embedding URL's into audio and video streams

Video Image Maps

• New: "hot spots" move in image
• Required: way for describing object movement
  • new image map with each image
  • function describing object trajectory
• Required: way for transmitting maps
  • attach to each frame
  • send seperately

Tracking and Contributing to IETF Work

• Audio/Video Transport Group (AVT)
  • RTP
  • Payload type definitions
• Multiparty Multimedia Session Control (mmusic)
  • Session Description Protocol
  • User location services
• MBone activities

Outlook

• Fall '96: Workshop
• MHEG evaluation (with help from Alcatel, DAVIC/Philips)
• Next AC Meeting (Dec. '96)
  • Draft "Display control"
  • Draft "Video image maps"
  • Draft "URLs for linking into audio/video"