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Comp Sci 1033 Video II Lecture: Compression, Streaming, Audio, Major Assignment

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Western University
Computer Science
Computer Science 1033A/B
Laura Reid

computer science lecturenovember 29, 2010 Video II Compression Concepts - Spatial Compression: - Compress each frame individually - Uses the same techniques as JPG compression - Codecs that do spatial compression are: Animation, PlanarRGB - Temporal Compression: - Just saves info on selected frames (called keyframes) - All other frames just save the difference between current frame and keyframe is small - Codecs using temporal compression are: Sorenson Video, H.264 - Container File Format: A file format that stores both the data (frames) and how to play the data (which codec use) - Some common containers: - avi: sometimes has uncompressed videeo, just depends - mov. - flv (swf is not a container file format.) - mkv (newest and open source. Allows you to store unlimited number of audio and video tracks. (english/spanish/french all in one avi file.) - Newer container formats support subtitles, chapters. Why can your computer sometimes play one avi file but not another one? - One was built for the codec your computer does have, the other is built for a codec your computer doesn’t have. - Digital Media Player: a piece of software that will play multimedia files (audio or video). - Most players will play a variety of file formats: ◦ - Windows Media Player (bundled with Windows 7). Some Features (e.g. supports streaming) - Windows Media Player Question:What is the Apple version of Windows Media Player for playing video files? - Quicktime - Question:What is the Apple software developed for playing audio files? - iTunes - Question: Can anyone name another player? - RealPlayer, VLC Three Ways of Getting Video to Computer - Need to know what streaming is for exam* - Three ways of getting video to computer: download, progressive download, streaming computer science lecture november 29, 2010 - Streaming: constantly sending to you, downloaded onto your computer just enough to play it, and then it’s erased from your computer later. It is never permanently on your computer - Media is either streamed or not streamed. - Television is streamed, radio is streamed, a book is not. - When you visit a website containing video, the entire video must be downloaded to your computer before you can play it. - Disadvantages: it takes up space from your hard drive, if you disconnect from internet you’ll lose the video, you could get a virus, it takes a long time (hours), it’s not permanent. - On Demand Streaming and Live Streaming: Live or not live basically. - You have to have a convert that will convert to a streamed video and a web server that will let you do streaming - Video is huge and you want people to watch it immediately so you have to do lots of compression. RTSP is a special server that lets you do this. - Progressive Download - A click begins the download, but after some portion of the file has been downloaded, the video will start to play and stores it on your machine - Advantages: you can watch it while you’re downloading it, you can go back and play it over again because it’s stored on your computer - Disadvantage: Your internet could stop working, if your internet slows down you have to sit and wait for it to download still - You have to end up with a video that has an RM extension (real medium) for streaming *EXAM - STUDY THAT DIAGRAM SHE SHOWED US AT THIS POINT - Unicast - each user gets own stream, several users get it at once - Which streaming website has revolutionized video? - YouTube: Anyone can watch, if you want to post videos you have to register, some videos only people over 18 can watch, there is automated softwar
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