Transcript 12Sound2
INF 240 - Web Design Using Multimedia on the Web Sound - Part 2 Downloading versus Streaming Two main ways to “deliver” a sound file to Web page: Download - download complete file, then play it. Streamed - “stream” file - listen in “real” time. Use streaming when - Presenting live events. - Sound requires very large files. - Need to save time - prevent user from waiting. When you download a media file - A copy of the file resides on your computer’s hard drive. - You can listen to it or watch it any time. - You can copy the file or share it! With streaming, Your computer does not save a copy of the media file. - It only saves enough in a buffer (aka memory) to keep the playback in the browser smooth and continuous. - You cannot save the media file, burn it, share it or take it with you! Streaming The Principle of Streaming Computer stores stream in a buffer – temporary memory Why use streaming? • Streaming allows for the delivery of high-impact, engaging, and, often, interactive content. • Streaming is typically very flexible and can be distributed widely in a variety of formats. • Standard video and audio content can be too large to deliver via traditional formats. - Streaming formats offer excellent compression and very effective delivery. Streaming media (whether audio or video) begins playing almost immediately after the request is made to the server, and continues playing as the audio/video data is being transferred to the browser. Streaming media technology was developed to address the problem of unacceptable download times for multimedia files. - It is good for broadcasting live events, such as concerts or football games – Webcasts, Webinars, ... Live Webcast What do the different streaming formats do? There are a number of different file formats for streaming media. • Each format uses a different algorithm for compressing and embedding the streaming data. • Different manufacturers place emphasis on different aspects of the multimedia: video, sound, speed, bandwidth, for their own format. • Because of the competitiveness of the different manufacturers, each format represents a different means of achieving effective multimedia streaming. • Common to virtually all streaming formats is the MPEG compression algorithm. • MPEG (Moving Picture Experts Group) develops standards for the compression of both digital video and audio. • The actual compression/decompression software is often referred to as a codec (coder/decoder). There are two types of streaming, pseudo and genuine streaming: - Pseudo (aka progressive) streaming is a form of downloading, but allows for immediate playback - the sound file plays while it is downloading. Pseudo streaming uses only pre-compressed data. - Genuine (aka true) streaming requires specialised server software and can compress the data on-the-fly, delivering content in an efficient format. Genuine streaming Genuine (or true) streaming relies on special server software that permits the “uninterrupted” flow of data. Uses the special Real-Time Streaming Protocol (RTSP), not HTTP. RTSP permits a two-way conversation between server and the browser player. - The browser user can request from the server content from the middle of a file, e.g. seeking ahead in long content, or begin playing from the middle of audio/video stream. Pseudo (aka Progressive Download) Streaming Deploying streaming media content with the standard Web server approach is actually only a small evolutionary step away from the download-and-play model. With pseudo streaming, the audio begins playing before it has completely downloaded, producing a streaming effect even when the file is served from a standard Web server. The advantage to pseudo streaming is that it requires no special streaming server. - The audio or video files are placed on a standard Web server and linked to from a Web page by the standard method. There is one big drawback to pseudo streaming: - because the file is being downloaded from a Web server (using the HTTP protocol), the user cannot skip ahead to a point, say, 14 minutes into the stream. To allow this interaction, must use genuine streaming - an actual streaming media server must be used instead of the normal Web server to provide genuine streaming. Limitations on Streaming types • Because video and audio data can be quite large, compression is an integral part of streaming. • Pseudo streaming uses pre-compressed files and only allows users to view the streamed media sequentially - you cannot skip to a set point in the stream. • Genuine streaming allows a user to navigate to any point in the stream, but requires dedicated server software to do this. Genuine streaming files must be prepared specially for delivery Genuine Streaming Metafiles Genuine streaming makes use of metafiles. • When you click on a link for a streaming media file, you are actually clicking on a link to a so-called metafile which is then sent by the Web server to your browser. • The metafiles contain a set of instructions (or just a URL) that tell the streaming media player in the browser how to connect to the (actual) streaming server to stream the requested file. the streaming server may be located separately from the Web server. What happens when you stream - Metafiles meta streaming True Streaming 1. Request for streamed audio Web Server Web Browser 2. Send meta file meta file 3. Request for stream Streaming Player Stream Server 4. Send stream Questions?