History of Video • Drama • A multimedia experience. How? • Film • First technology to capture the multimedia experience of drama in a form that could be widely distributed. • Television • Offered a way to capture the combined media of voice, image, gesture, music, and motion (just as film did) • Distributed via electronic signals rather than via film • Today • Television and Movies are broadcasted as well as saved and distributed.
Role of Video on Websites • Telling a Story (example) • Entertainment (examples) • Explanation (example) • Personalization of the web experienc
Check Out Video On Your Own • Head on over to CNN, iFilm, Quicktime Movie Trailers. Check out the videos there.
Limitations of Video • File Size can be HUGE • Takes a while to download • Requires plugins
How Video Works on the Web • Video on the web works differently from film, tv, and video tape. • Uses different technologies and different storage and transmission methods • Video on the web is fully digital • Goes through significant compression • Can be downloaded as a file or streamed to the audience. • Its file formats and codecs are complex • Be sure to read pages 108-111 for this! • There is a lot of info on how video works
Video Compression • Repetition and Patterns • Say we have a video of a horse running. The movement of the horse’s legs is the same step after step. • The codec recognizes this repetition of a string of numbers over several frames that form a repeated pattern (the horse’s moving legs). • The codec saves this data using a “ditto, 319 more times”, or using a single number token to represent the repeated pattern. • Relatively lossless
Video Compression • Averaging • Same method a JPEG uses • Looks at a block of pixels and averages their color and brightness, saving one number rather than 4, 9, 16, etc. (see chapter 1 and 2 for more info on averaging)
Video Compression • Range Reduction • The range in brightness of an original video might be on a scale of 1 to 500, meaning that the lightest part of the sky is 500 times brighter than the darkest shadow under a forest. • This brightness is recorded as a number for each pixel in each frame • Wide range of brightness requires that a big number - 8 or 16 bits - be recorded for each pixel. • The codec reduces the range to a scale of, say, 1 to 100. The sky is still brighter, but only 100 times or so brighter. • Because the number is saved millions of times in the movie file, reducing its size can delete lots of data from the file…most people will not notice this range reduction.
Video Compression • Frame-Difference • For the first frame of a video, every pixel is recorded. For subsequent frames, only those pixels that have changed are recorded.
Downloads vs Streaming • Downloading • Simplest method. User downloads file, when file is finished downloading, user watches file. • Fast-Start Downloading • Video file downloads to the viewer’s computer but begins playing as soon as the first few hundred frames have been received. • Works well for small and medium sized videos.
Downloading vs Streaming • Streaming • Displayed on the screen as soon as it arrives on the user’s computer. • It is not downloaded to the hard disk. • A streaming video server manages the connection with the user, monitoring the reception to ensure that the video is arriving fast enough to provide good viewing • Makes use of data buffering. (temporarily storing portions of the data)
File Formats • Downloadable Video • QuickTime (.mov) • Moving Picture Experts Group (.mpg) • Audio-Video Interleaved (.avi) • Windows Media (.wmv)
File Formats • Streaming Video • RealVideo (.ram) • QuickTime (.mov) • Windows Media (.asf)
Preparing Video for the Web • Sources: • Camcorder and video tape (both require video capture software) • DVD • TV • CD-ROM • Web video • Video from still images. • We will use: Windows Movie Maker.
Adding Video to your Webpage • See pages 132-134 • Be kind to your users!