T7L3

Video

Introduction

Audio and video on the Web are now common occurrences. Like with many things that rapidly develop, you will encounter good examples and poor examples. The key to producing and delivering good video on the Web is to start with good content. At times this may mean getting professionals to author, shoot the video, edit , digitize, and prepare for delivery. Once a good video is ready, it is then necessary to deliver it the way it was envisioned. Web delivery may not always be the best solution. Planning for how a video is to be delivered is of great importance right from the beginning of a project. Each of the team members needs to have a basic understanding of the strengths and weaknesses of video on the Web.

This unit of instruction focuses on the basic concepts of how video (in this case, audio may or may not be part of the video clip) is prepared and delivered on the Web. See the following lessons for related information:

  • Animation [[link to animation]]
  • Streaming Video [[link to animation]]
  • Audio [[link to audio]]

By the end of this lesson you should be able to:

  • List the basic hardware needed to create digital video.
  • List the basic software needed to create digital video.
  • List basic digital video concepts.
  • List the common digital video file formats.

This lesson will cover:

  • Basic Hardware for Video Processing[[link to single html page on this]]
  • Basic Software for Video Processing[[link to single html page on this]]
  • Basic Digital Video Concepts[[link to single html page on this]]
  • Digital Video File Formats[[link to single html page on this]]

To round out your explorations, make sure you complete the last two sections:

  • Activity[[link to single html page on this]]
  • Video Summary [[link to single html page on this]]

Additional Resources

WebMonkey - Audio and Video [[

Video for the Web Site [[

Web Codecs & Example Compressions[[

Apple Quicktime [[

DV [[

Basic Hardware for Video Processing

Here is the common basic desktop hardware used to prepare video for web delivery.

Basic Hardware

Regardless of platform, you should have plenty of RAM and hard disk storage space. Processing and storing video takes plenty of both. Obtain as much as you reasonable can.

Do not confuse the video RAM of your machine with the ability to create, play, or download digital video. Video RAM has to do with the amount of data your monitor is capable of displaying at a given time - resolutions, number of monitors, etc.

Macintosh

Macintosh G3 and G4 platforms usually have built in digitizing boards capable of digitizing video. Additional hardware can added as needed.

PC

PC machines usually need to have additional hardware to be able to process video. Many times resources can be found in trade journals that will guide you through this process. Generally this is done with a digitizing card.

In both cases, CPU speed and storage capacity are issues. More recently with the increased acceptance of IEEE 1394 (Firewire) formats, additional hardware may needed to capture the digital video (DV) information

In addition, specialized formats such as MPEG may require the use of an additional hardware component to complete the compression process in a timely manner.

Reflective Questions

[[Objectives

After reading the above information and answering the following reflective questions, you should be able to:

  • Explain why many computers do not come with built-in digitization cards.
  • Explain why it is useful to have a large hard drive when processing video.]]

1. Why don't many computers come with built-in video digitization cards?

2. Why should you have a large hard drive when you process video?

[[reflective questions can be shared in a CMC format at the instructor's discretion]]

Basic Software for Video Processing

Here is the common basic desktop software used to prepare video for web delivery.

Capturing

The next step in the multimedia video process is to get the video from the tape into your computer. Generally this is done with software that activates a digitizing card and gives you options for the process. When your video is captured, it is transferred from tape, digitized, and stored in a file or group of files, usually on a hard disk. The following is a list of vendors selling or involved with digitizing cards and software:

  • Adobe Premiere [[
  • Apple Quicktime [[
  • Avid: Makers of Avid Media Composer systems [[
  • Avid Cinema: Makers of the turnkey Avid Cinema [[
  • Data Translations: Makers of Media 100 video capture hardware [[
  • TrueVision: Makers of TARGA 2000 video capture hardware [[
  • Digital Origin: Makers of VideoVision and Telecast. [[
  • Miro: Makers of the miroDC20 [[
  • Windows Media [[

Adding special effects and compositing are usually done as part of the editing process. Here is a short list of editing, special effects, and compositing software vendors:

  • Adobe Premire [[
  • Apple Final Cut [[
  • Adobe After Effects [[
  • RotoDV [[

Compression

This is a special process that prepares the finished, edited video clip for delivery. It consists of using COmpression/DECompression (codec) software (and sometimes hardware) to crunch the file into a manageable size.

  • Apple Quicktime [[
  • Media Cleaner Pro [[
  • Real System [[
  • Sorenson [[

[[can we show a pict here of the video input (from tape), digitizing, and output (to disk process?]]

Reflective Questions

[[Objectives

After reading the above information and answering the following reflective questions, you should be able to:

  • Explain the difference between analog and digital video processing.
  • Discuss why several types of compression schemes are used.]]

1. What is the difference between analog and digital?

2. Why are there several different types of compression schemes?

[[reflective questions can be shared in a CMC format at the instructor's discretion]]

Basic Digital Video Concepts

Movie Length

The important feature here is to realize that the computer is not a television. Each technology has its strengths and weaknesses. For example, the computer is more flexible and can offer interactivity that is not available in a linear TV or film production. The drawback is the bandwidth available to deliver the content in the desktop environment. A minute or two of video can lead to prohibitive download times because of the large file sizes required to capture all of the information adequately. If a large movie length is needed, then alternative delivery methods should be considered. Alternate solutions may include DVD, CD-ROM, or Streaming video if it is necessary to serve it via the web. [[note: provide link to streaming video]] Generally, short video clips should be used on the web.

Frame Size

In addition to movie length, frame size is the next reason for large, prohibitive file sizes requiring lengthy download times. The standard frame size for a full screen video is 640x480 pixels and is prohibitive for almost all Internet applications. Some recent compression applications can now compress short video clips well enough at 1/2 frame size (320x140) to be delivered via the Internet, but generally the average frame size used is 160x120 pixels or less. Limits to what is exactly possible are directly dependent on CPU power and the bandwidth of the Internet link that the projected end user will have. As an alternative, streaming video may provide a solution for large frame size if CPU and bandwidth will permit.

Frame Rate

Frame rate is the number of frames per second (fps) the video is to playback in. As a comparison, the TV-quality frame rate is delivered at 30 fps to create smooth movement. For the Web, a fps of 15 or even 10 is more appropriate. A fps of 15 or 10 is still capable of producing fairly smooth video playback. Under special circumstances, an even lower fps is used for talking heads (basic still shots of people's faces) or anywhere there is a low amount of movement. Commercial broadcasts may even use 0.5, .025, or even 0.05 frames per second.

Quality

Quality (how real does the movie look) can be controlled and set in many video-editing programs. Compression algorithms that crunch and discard data (called lossy methods) are controlled by setting the degree of the desired quality. As a general rule of thumb, the lower the desired quality chosen, the higher the compression and consequently, the lower the bandwidth requirements and the smaller the clip. Frame rate and quality are often traded off to reduce bandwidth requirements.

Color Bit Depth

Video file size is also directly affected by the number of colors used. A 24-bit color file will much larger than an 8-bit file. Of course, reducing the color bit depth will sacrifice image quality. See the Introduction to Graphics on the Web lesson for more information on bit depth and color [[link to T3L8]].

Data Rate

The data rate is the rate of which the video is transferred in order for it to be displayed smoothly and without interruption. The data rate or "bit rate" is measured in kilobytes per seconds ("K/sec" or "kps"). The data rate is calculated by dividing the file size in kilobytes (or "K") by the length on the movie in seconds (sec). For example a movie file size of 1900K (1.9 MB and is 40 seconds long has a data rate of 47.5 Ksec (1900K / 40 sec) = 47.5 Ksec). From this the server can determine how long a movie will take to download to the users desktop computer. Many compression programs allow you to choose the type of target bandwidth desired and determine the appropriate bit rate for smooth playback.

Compression Schemes

Digital video delivered on the Web would not be possible without sophisticated data compression routines because of the high volume of data involved to describe sound and image information contained in each video frame.

Two major schemes are used when compressing video. Compression codecs may use a combination of these schemes in their algorithms to achieve the best results.

Lossless Versus Lossy Compression

"Lossless" compression simply means no data is sacrificed during the compression and the file contains exactly the same information as the original.

On the other hand, "Lossy" compression sacrifices some data from the file to achieve a higher compression rate. For example, MPEG compression can use algorithms that toss out information from the sound and video detail that is not discernable to the human senses. When the file is decompressed and played it is very similar to the original file to human eyes and ears. This is similar to the way that JPEG handles still images.

Spatial versus Temporal Compression

Spatial (or intraframe) compression takes place on each individual frame, compressing each individual frame as if it were a still image.

Temporal (or interframe) compression happens over a series of frames and takes advantage of areas of the image where relatively little change occurs from frame to frame, throwing out pixel data that is repeated.

Temporal compression relies on the placement of key frames placed throughout the frame sequence. Key frames act as master frames against which the following frames (called Delta frames) are compared. A key frame usually is identified for each second of video. A clip with a 15 fps frame rate would have a key frame every 15 frames. Videos without a lot of motion take the best advantage of Temporal compression schemes.

Compression/Decompression Algorithms

Compression/decompression (commonly known as codecs) algorithms are commonly used to prepare video for the Web. Video-editing software offer long lists of codecs. Here are a few of the codecs commonly used for Web delivery.

Sorenson [[

The Sorenson Video Codec produces excellent Web video suitable for playback on any Pentium or PowerMac. It produces the highest quality low-data rate QuickTime movies. Quicktime 3.0 began supporting Sorenson in 1998 and it has gained wide acceptance.

Real System [[

RealSystem G2 uses the RealVideo G2 with Scalable Video Technology (SVT) as its video codec. RealSystem G2 is a streaming architecture, offering both server-based "true

streaming" and serverless "HTTP streaming" (also known as "progressive download").

See the lesson on Streaming for more information. [[link to T7L4]]

Animation

If your video is all computer-generated graphical imagery (i.e. not sourced from video tape), then you might want to use an animation compressor.

MPEG

The MPEG codec primarily uses a lossey compression. It is not generally compatible with other formats. However recent developments for MPEG4 are currently under development and are to be based on Apple's Quicktime [[ Some later versions of Quicktime provide MPEG support. MPEG is known for its high quality video; however, it requires a fairly fast computer to play well.

Reflective Questions

[[Objectives

After reading the above information and answering the following reflective questions, you should be able to:

  • Evaluate when high quality video playback is necessary regardless of file size costs.
  • Describe when video must be used on a web site.]]

1. Under what situations would you insist on high quality video playback, regardless of the cost in terms of file size?

2. When would you insist video must be used on a web site?

[[reflective questions can be shared in a CMC format at the instructor's discretion]]

Digital Video File Formats

Just as still images have many different formats that have many different file extensions, so do video formats. However, not all of the formats are appropriate for delivery on the Web. Here we look at some of the more common formats the are currently compatible with Web browsers. These are generally installed into the browser as an extra piece of software called a plug-in. See the lesson on Browsers for more information on plug-ins [[link to T2L4]]. In this case, the plug-in serves as the decompression software part of the codec that is needed to translate the video and audio information. Plug-ins for video processing are generally associated to a particular file type and key in on the extension to know what video file format to interpret. Some browsers supply the plug-ins with the browser and are installed automatically. As plug-ins become outdated the user is often prompted to go to the vendors Web site and retrieve an update. The number of plug-ins available can be large, and a reference link to the appropriate vendor should be supplied on the page where the video is to be displayed. A video format extension can also tell whether a video file is being streamed or not.

Name / Platform / Supports / Information
RealPlayer
by Real Systems / Available for Macintosh, PPC, Win16, Win95, WinNT, OS/2, IRIX, SunOS, Linux / Support MIME types:
audio/x-pn-realaudio-plugin
Support file extensions:
.ra, .ram, .rpm / RealPlayer provides live and on-demand real-time RealAudio and RealVideo streaming content on the Web. Experience RealAudio broadcast-quality stereo over 28.8Kbps modems, AM-quality at14.4Kbps, and near-CD-quality audio at ISDN and faster
connections. RealVideo delivers newscast-quality video at 28.8 Kbps and full-motion at faster connections. A powerful plug-in is
included that lets Web authors easily customize and deliver
exciting multi-media from their sites.
Apple QuickTime 4 Plug-in by Apple Computer, Inc / . Available for Macintosh, PPC, Win16, Win95, Win98, WinNT / Support MIME types:
audio/aiff, audio/basic, audio/midi, audio/mpeg, audio/wav, audio/x-aiff, audio/x-midi, audio/x-mpeg, audio/x-wav, image/png, image/tif, image/x-bmp, image/x-macpaint, image/x-photoshop, image/x-png, image/x-sgi, image/x-targa, image/x-tiff, video/avi,
video/flc, video/mpeg, video/quicktime, video/x-mpeg, video/x-msvideo
Support file extensions:
.aiff, .au, .mpeg, .wav, .aif, .mid, .png, .tif, .tiff, .bmp, .ptng, .png,.targa, .avi, .flc, .mpe / The Apple QuickTime plug-in lets you experience QuickTime animation, music, MIDI, audio, video, and VR panoramas and objects directly in a Web page. The Apple QuickTime Plug-in's "fast-start" feature allows you to experience QuickTime content while it's downloading. It works seamlessly within firewall environments and requires no special server software.
Bamba by IBM / Available for Win95, Win98, WinNT, OS/ / Support MIME types:
audio/x-ibmbamba
Support file extensions:
.iba / Bamba is an audio-video streaming tool that supports high-quality audio-video streaming for low-bandwidth connections. Bamba contains algorithms that determine connection bandwidth and file size, then make adjustments to maximize the transmission of
audio-video data. The result: a typical PC user with a 14.4 or 28.8Kbps modem can easily download and view large audio-video files. With Bamba, audio-video clips arrive in streams so that users will begin to view or hear the clip before download is complete.

[[Note: Source link

Reflective Questions:

[[Objectives

After reading the above information and answering the following reflective questions, you should be able to:

  • Explain why Apple’s Quicktime digital video file format is so popular.
  • Explain why plug-ins are needed to play back video on the web.]]

1. Why is Apple's Quicktime format so popular?