(T) One of my engineers who moved last year from China to Silicon Valley watched the entire Olympics Games on the Internet since she did not have at that time any TV set in her new California home. Videos are now everywhere on the Web. We watch them every day on the New York Times or on any of our favorite news sites. We upload and download them every day from YouTube or from any of our favorite video sharing sites. But we are not always aware of the underlying technologies which enable us to take a video, upload it and watch it on YouTube. So following is a small tutorial to better understand that process: Video Demystified in a nutshell!
The first key video technology is the coding scheme or CODEC. Simply put, CODEC defines how videos, images and audio are created into binary data. CODEC algorithms enable to compress and decompress videos, images and audio. Compressing generally refers to as encoding while decompressing generally refers to as decoding. Frequently, videos are converted from one type of CODEC to another one: this process is called transcoding. Compression can be lossless if the input and the output are the same or lossly if not.
Popular video codecs include Flash from Adobe, H.264 standardized by the ITU-T, and VP6 developed by On2 Technologies. Popular image compression algorithms include the Joint Photographic Experts Group (JPEG), the Graphics Interchange Format (GIF) and the Portable Network Graphics (PNG). Popular audio codecs include MP3 or MPEG-1 and MPEG-4 standardized by the Motion Picture Experts Group and the AAC/AAC+ standardized by the ISO/IEC.
Videos on YouTube are generally encoded into Flash or H.264 codecs while most of the videos on broadcast news and sport sites are encoded into VP6.
Videos are embedded into a container used to identify the inner media content. The container specifies how the video and the audio content are mixed. It might also include additional content such as menus, chapters, subtitles, and any other data from the video designer.
Popular multimedia containers include Flash Video (.flv) from Adobe, Advanced Systems Format (.asf, .wma, .wmv) from Microsoft, 3GP (.3gp) for mobile devices standardized by 3GPP, MP4 and MPEG (.mp4, .mpeg) standardized by the Motion Picture Experts Group, and QuickTime (.mov, .qt) from Apple.
Videos and audio are played and images are watched in a player on your desktop or mobile computers. Mac computers uses the Apple Quicktime player while Windows computers uses the Windows Media player. Flash players from Adobe are usually used to play videos in an application embedded into a Web page such is the case with YouTube. Another popular player is the open source VideoLan or VLC media player.
Videos that are watched from YouTube are delivered from the YouTube site to your desktop or mobile device as “progressive download” over the HTTP protocol. Progressive download sends small chunks of video data to the client media player. Videos can be as well delivered over a streaming protocol in particular RTSP (Real-time Streaming Protocol) that leverages RTP (Real-time Transport Protocol) for the transport of the video and audio and RTCP (Real-time Control Protocol) for the control of the video and audio transmission. RTSP, RTP and RTCP are also products from the IETF. Another popular streaming protocol is Adobe’s RTMP (Real-time Messaging Protocol).
The typical YouTube video clip is 320 kps while MySpace is 400 kps and news and sports video clips are between 500 and 600 kps.
So as a conclusion…
When you transfer a video from your digital camera to your computer, the video has ben encoded and is stored in a given codec and container format function of your digital camera. If you edit your video into an Application such as Apple’s iMovie, iMovie might transcode your video and stored it in a QuickTime container.
When you upload your video to YouTube, you transfer your video from your computer to YouTube over HTTP. YouTube might transcode your video into a Flash or H.264 codec. Finally, when you watched your video on your computer from the YouTube site, your video will be played into a Flash player embedded into a Web page and again delivered to you over HTTP.
Note 1: Most video standards have been the products of multiple or joint standard organizations.
Note 2: The picture above is from Vanessa Mae – playing The Devil’s Trill…
And playing Toccata & Fugue, accompanied by the Bratislava Radio Symphony …
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Categories: Video, Audio, and Other Media