Quicktime Howell Istance School of Computing De Montfort University.
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Quicktime Howell Istance School of Computing De Montfort University
What is QuickTime? Many different schemes for encoding digital video, unlikely to obtain agreement on any one universal format better approach is to define an architectural framework which can accommodate various specific representations QuickTime is a component-based, cross-platform architecture, introduced by Apple in 1991 - has now become a de facto standard Streaming included in QT4.0 (1999), QT4.1 supports SMIL
Consists of two main managers - the Movie Toolbox and the Image Compression Manager + a set of components Movie Toolbox –applications gain access to QT facilities by calling functions from the toolbox –allows the application to store, retrieve and manipulate time-based and provides functions for editing movies Image Compression Manager –provides device independent and driver independent means of compressing and decompressing images –usually accessed via Toolbox functions
Software components (in general) a packaged software object which can be conveniently re- used in applications should be in some binary form (i.e. not source needing to be compiled each time) should have a clearly documented programming interface to enable its integration with other applications the creation of components should ideally be supported by special development tools or high level libraries should conform to some agreed or de facto standard may be a commercial saleable item or may be freely distributed
QuickTime Components Movie controller components let applications play movies through a standard user interface. Image compressor components compress and decompress image data. Image transcoder components convert compressed files from one format to another. Video digitizer components let applications control video digitization by external devices. Movie data-exchange components let applications move various types of data into and out of QuickTime movies.
QuickTime Components Video output components convert QuickTime movies into video streams. Media handler components implement the behavior of different track types. They deal with the specifics of how a particular track's media data should be presented to the viewer. Video media handler Component implements video tracks by calling the Image Compression Manager to display video samples. Sound media handler Component implements sound tracks by calling the Sound Manager to play sound samples.
Movies Abstraction of a sequence of video and other media elements movie file contains a movie and bundled media data, or references to url’s where data can be obtained from each movie has a time base which records the rate at which it should be played back at and a current position timebase is synchronised with a clock on the local system, ensuring correct playback speed if frames can not be played fast enough, some are dropped to ensure maintenance of correct playback rate
Movies and Time Scales Movie timescales unified to second boundaries media timescales translated to movie timescales automatically
Movies -playback Rate determines how many time scale units actually run per real-time unit. Movie shown has a time scale of 600 running at a rate of 0.5. The movies duration is 1200 and contains a transition between two tracks (Graphic A and Graphic B) at time 600.
Tracks and Media The audiovisual parts of a QuickTime movie are its tracks. Each enabled track tells QuickTime how to fetch and present chunks of digital media. Tracks contain a list of references, which identify portions of the media the track uses. These references are called edit lists. This allows flexible access to media; a track can play the underlying media data in any order and any number of times. Layering refers to how tracks can overlap one another, layering several images to produce what the user sees
Overview of Criteria for comparing media formats Interactive Capabilities Browser compatibility Software Cost for streaming and encoding Level of documentation and support Media encoding and content generation Media authoring and delivery Low bandwidth performance Server performance and quality of software tools for large scale streaming
Interactive Capabilities Is the presentation intended to support a high level of user interaction, (rather than continuous broadcast) – and support audio interaction effects (e.g. sound on rollover) Excellent - Flash and Director Shockwave Fair – Windows Media, Real media, Quicktime Limited/none – MP3
Browser compatibility Will target audience have required plugin or helper technology to support version of format used? Is it likely they will be willing/able to download this Excellent – Real Media, MP3, Windows Media, Quicktime, Flash, MIDI Fair – Director Shockwave
Software Cost for streaming and encoding RealMedia – free for Basic version (25 streams), but full RealSystem server professional (100 – 2000 streams) starts at $6000 Windows Media – free (must have NT/Windows 2000) QuickTime – free to encode, large scale managed streaming requires Mac OS X server, starts at $1000 Flash, Director – license cost, no dedicated server required MP3 – free to cheap
Level of documentation and support Real Media – excellent Windows Media – good Quicktime – fair MP3 - limited