Dan LaValley Manager Biology New Media Center

Thanks to Dan LaValley of Learning Technology & Distance Education for creating this tutorial.

1. Brief Guide to the Technology
2. Media Delivery Methods
3. Media Delivery Mechanisms

 

 

Brief Guide to the Technology

There is an array of choices for delivering multimedia, and all of them have strengths and weaknesses. In this section you will be introduced to some names and acronyms for audio and video formats.

Formats and Their Suffixes

Audio Formats

• Audio interchange format - .aif, .aiff
• MPEG 1 layer 3 - .mp3
• Windows sound file - .wav

MPEG (Motion Pictures Expert Group) video
MPEG, a video format developed as a standard, is accessible by many players. For example, MPEG1 videos can be played in most major desktop video players including QuickTime, Real, and Windows Media Players.

• mpeg1 - .mpg, .mp1, .mpeg - used for CD video
• mpeg2 - .mpg, .mp2 - used for DVDs
• mpeg4 - .mp4

QuickTime
QuickTime is the first video technology for computers and the web. QT has been around for over ten years and has evolved considerably since its inception. Its newest version is moving forward to support the new MPEG4 standard.

• QuickTime movie - .mov, .qt,
• Other QuickTime file types - .qti
• QuickTime "pointer" files - .qtl
• QuickTime SMIL - .smil, .sml, .smi

RealMedia
RealMedia is the first video technology that streamed. It has also adopted support for the MPEG4 standard.

• Real Video - .rm,
• Real Audio - .ra,
• Real Media "pointer" file - .ram
• Real SMIL files - .smi, .smil

Windows Media
Windows Media is the newest computer video technology, but anything that has the force of Microsoft behind it is something to be reckoned with.

• Video for Windows - .avi
• Windows Media Audio - .wma
• Windows Media video - .wmv
• Advanced streaming format - .asf
• Advanced streaming "pointer" - .asx
• Synchronized accessible media interchange -.smi (not SMIL)

SMIL
SMIL is a technology that allows the designer to combine media elements (audio, video, pictures, text, and others) in a time-based manner. There is a similar format called HTML+Time that is supported by Microsoft.

• SMIL files - .smi, .sml, .smil

Terms

• 4:3 Aspect Ratio
  The common ratio of width to height of most televisions and computer monitors. Videos of 640x480 or 320x240 pixels are examples of this aspect ratio.
• 16:9 Aspect Ratio
  The ratio of width to height found in movies, DVDs, and in the new high definition TV standard. The native resolution is 720x480 pixels.
• Bandwidth
  The amount of information that can be sent and processed per unit time. This is usually measured in kilobits per second (kbs) so for example a modem has a theoretical bandwidth of 56 kbs, while the slowest form of ethernet has a maximum bandwidth of 10,000 kbs (10 megabits) - remember that there are 8 bits in a byte of information, most files are measured in bytes (kilobytes, megabytes, etc.).
• Cinepak
  One of the very first CODECs (see next) that allowed video to be compressed at a fairly high rate for its day. It still has a few advantages in that a movie compressed in Cinepak can be played in many different video players.
• CODEC
  COmpressor-DECompressor (COder-DECoder) - there are many CODECs and they use a variety of technologies to reduce the file size of the video and audio files while attempting to keep the quality as good as possible. They vary with the technology used, but there are some shared CODECs.
• CBR (Constant Bit Rate) encoding
  The encoding software attempt to keep the total bits/second constant through the entire video. This makes the size of the file predictable and easier to stream. Most modern CODECs will allow you to set an upper threshold on the bit rate and allow the rate to drop when it is not required for quality to help reduce the amount of bandwidth used.
• Data rate
  The amount of information used to represent the video and audio. Confusingly, it is sometimes represented in kilobits per second (kBs) and sometimes in kilobytes per second (kbs).
• Frame rate
  The number of individual pictures per second (FPS) making up the video, the more pictures per second the smoother the motion appears, but also the larger the file will be. Television plays at 29.97 FPS, while most film is only 24 FPS. Web video is usually 15 FPS or less, though this increasing as bandwidth increases.
• Frame size
  This is simply the size of the images in pixels. In the United States, full sized video is generally either 640x480 pixels or 720x480 (the new, uncommon wide screen format).
• Key frame
  Part of a compressed video that contains the complete information of picture. The frames that occur between two key frames only contain information that represents the change that occurs from one frame to the next, thus greatly decreasing the amount of information needed and reducing the file size.
• Kilohertz (kHz)
  The unit of measurement for audio frequency (also known as cycles per second -cps).
• Kilobit (kb)
  1000 bits or 125 bytes.
• Kilobyte (kB)
  1000 bytes or 8000 bits.
• Multicast
  A server sends out a single stream of data to which many recipients connect to (much like television or radio). Compare to unicast (below) it is far more efficient in bandwidth usage.
• Noise reduction
  A "filter" used to reduce unwanted noise from video to audio signals. In video, noise is reduced by slightly blurring the picture. In audio, the filtering in more complex, but it can help remove unwanted hiss and pops.
• Progressive download
  An http "streaming" technology where media is served from a standard Web server and downloaded to the client machine. Depending on the preparation of the files, you might be able to begin playing the content before the download is complete, but you can not get to the very end of the file until it is downloaded.
• RTSP (Real Time Streaming Protocol) streaming
  Like a broadcast radio or television signal, media is delivered and played, but not stored on the client machine. Because the server delivers the content just as it is needed it is possible to skip directly to the end. It requires a special server. Both QuickTime and Real support this standard. Windows Media uses a different protocol, but can do exactly the same thing. This format can be multicast or unicast.
• Sample rate
  The number of samples per second of audio taken measured in kilohertz. The higher the sample rate, the better the sound is represented at higher frequencies but, the larger the file will be.
• Sample size
  For audio, the number of bits of information recorded for each sample. Most current audio CODECs work with 16 bit sampling (32,000 samples per sampling interval). In applications where less quality is required you might see 8 bit sampling (256 samples).
• Streaming
  Delivery of media over a network. It can be done either through progressive download or RTSP streaming.
• Unicast
  Recipients make individual requests to a server. Each request is fulfilled individually so each request takes a chunk of the available bandwidth.
• Variable bit rate encoding (VBR)
  A method of encoding video that first analyses the video and then compresses it. While it can take up to twice as long to encode the video, they are compressed at an optimal rate for the smallest file size. The variability in the data rate of the data stream does not make it appropriate for RTSP streamed content, but good for progressive download or video on CDs or other physical media.

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media Delivery Methods

Audio Only

The advantage of using only an audio track and no graphical element is smaller file size.

This method of delivery is appropriate when the content is not visual (for obvious reasons). Cases where this method of delivery are recommended include sound recognition training in language or music, or for redelivering some forms of lecture content. It is also a valuable alternative for very low bandwidth situations.

Illustrated Audio

This kind of delivery uses a series of still images that are synchronized with the audio. So it keeps file sizes smaller while allowing more visual content.

This provides the best format for delivering most forms of lecture content. It contains a set of images synchronized with an audio track. Some tools will allow additional low bandwidth annotations such as text, highlighting tools and simple animations.

Video

To deliver materials via video format adequate Internet bandwidth is required. It is best suited for content where motion is required to understand the principles demonstrated. As the bandwidth available to your audience increases the decision to use video format will become easier. High speed Internet is not yet universal, so be sure you understand your audience before adding too much video.

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Media Delivery Mechanisms

Internet (Lan vs. Modem)

HTTP "streaming" or progressive download
This format is good for short clips or clips that require very high quality. If the file size is large, your students will need a fast, reliable Internet connection such as cable or DSL.

RTSP streaming
This format is good for files that require copy protection because it is difficult to copy these files. The quality of the media depends on the Internet connection of your audience.

CD-ROM

Data CD
Standard CDs playable in most computers

Video CD
Video CDs use a special CD format that uses MPEG1. Most computers can play Video CDs with special software. Some DVD players can play them. The quality is comparable to VHS video.

Super Video CD
MPEG2 video is written to a CD so it is high quality. Only a small portion of video can be fit compared to a DVD. Super Video CDs require special software on computers, and some DVD players are capable of playing them.

DVD

DVD is rapidly growing as the format for delivery of commercial entertainment, and increasingly for educational and professional content. A DVD (depending on type) can hold several hours of high resolution video. Increasingly, desktop computers are coming equipped with DVD writers capable of producing video and data DVDs.

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