The new world of digital video is better than ever and today's workstation clients such as Real Audio Player 8.0 provide slick audio and video presentations via the Internet. In addition to being another avenue for entertainment, video streaming serves as a practical medium for training and education.
General Dynamics demonstrated this new technology by recording and then placing online most of the speaker sessions at Connecting Technology, Fall 2000. To enhance enjoyment of this budding technology, I'll introduce you to some video streaming basics including the equipment that is used to produce and play it, based on my experience.
What is Video Streaming?
Video streaming makes audio, video and other multimedia available in real-time over the Internet (or company intranet) with no download wait or no file to take up space on your hard drive. A continuous stream of data produces the video image that you see. Each bit of data contains a small portion of a video frame. Video files are commonly known as AVI (Microsoft's standard) or MOV (Quicktime standard). The data can be "streamed" from a hard drive, through a network, over the Internet, and even from a satellite. A personal computer (PC) assembles and decodes these individual data bits into a displayed video frame sequence on the screen. A commercial application of video streaming is the relay of television channels through satellite transmissions directly to a small backyard "dish" and then to a viewer's television.
Currently there are many variations of video streaming methods. Cable satellite operators, for example, have chosen either the MPEG 1 or MPEG 2 standard, which is similar to MPEG movies that you may have played on your PC, perhaps using Microsoft's Media Player. The only difference between MPEG movies played on your PC and satellite television channel streaming is the method the file actually "streams" from its source to the central processing unit (CPU) in a satellite receiver or home computer.
Video streaming is a challenge to produce simply because movies must be played at least 15 frames per second to appear in motion to the human eye. By comparison, television rates normally flow at 30 frames per second (fps); so moving images appear quite smooth.
An original uncompressed AVI or MOV file contains discrete data for each pixel in a video frame. The challenge is to move (stream) tons of digital data quickly enough to completely fill each video frame at the rate of at least 15 frames per second. The standard National Television Standard Committee (NTSC) frame contains 320x240 lines of resolution. A computer rendition of these lines of data means that a single picture frame must contain 320x240 individual pixels or in other words 76,800 total pixels or bits of data. Since the ideal is for a smoothly flowing video, this means that 76,800 pixels must be updated at a minimum of 15 times per second. That translates to a need to stream roughly 1,152,000 bits of data per second.
Moving file data this quickly from a hard drive through a satellite, LAN or high-speed Internet connection may not be a problem; but if you have a dial up or Internet connection moves data at only a rate of 5k or 6k per second, there are some real challenges trying to display smooth video with a screen size of 320x240.
File Compression and Encoding Algorithms (codecs) to the Rescue!
One solution to this problem is to reduce the frame size, but when the image is displayed on a screen with a resolution of 1024x768, a frame size smaller than 320x240 would appear too small. But increasing the frame transfer speed on a slower connection so that video remains smooth and reducing the number of bits required to transmit each frame will solve the congestion and speed problems. Compressing files removes duplicate information at every other bit location. So instead of 1,152,000 separate bits of information per frame, the size is reduced approximately 50 percent.
This reduces the streamlining requirement and the overall definition of the image is still acceptable, but that's still not enough. Encoding an AVI with an algorithm, called a codec (MPEG, MPEG 2, etc.,) further reduces file size. Codecs are software drivers with instructions to the CPU, to inspect each vector of the video frame for duplicate bit information and to strip out the duplicate frame bits from the file. For example, in an image of a person sitting still in a chair, there isn't a need to send 15 frames per second of duplicate information for that portion of each frame when it hasn't changed. For that reason, when the file is originally encoded using the MPEG2 codec, the algorithm instructs the file to retain this data only once in the file, along with instructions to the CPU to reuse this same data on subsequent frames when it's decoded for viewing using the same codec. Several different codecs used with raw, uncompressed AVI video files are: MJPEG, MPEG1, MPEG2, Cinepak, Indeo, RealVideo, ASF, etc.
There are many algorithm standards available today, similar to MPEG technology, and there are various companies who are continually developing new codecs offering improvements in performance especially using low-speed connections. General Dynamics worked with Network Designs, Inc. and Real Networks to create the video streaming for CT. Real Networks provides their video player device online at no cost to users.
Real Networks has developed it's own proprietary codecs for video streaming applications, the RA or RN file format. The technique they use, places video on a Web server, which streams to a user with a 56k modem. The results are outstanding. By reducing the overall screen size slightly and using extensive buffering during playback, smooth uninterrupted high-fidelity audio is possible along with video that runs with minimum hesitation. If network congestion does occur, the audio takes priority and the picture just drops a few frames to keep up.
Using MPEG 2 methods, the image on the screen actually contains vector components that are reused and do not have to be streamed on each and every frame. That cuts down quite a bit on the file size and the amount of actual data that needs to be streamed from its source. It's the combination of compression and using file algorithms during file development, or encoding that enables a smooth video stream through slower Internet links.
How to Produce Digital Video and Streaming Files
There are several software packages used to capture, edit, and produce digital video. Software, such as Adobe Premiere, a popular video editor, can capture, edit and produce a wide variety of movie file types such as AVI, MOV, etc. To capture video, a "capture card" must first be installed in your system. Capture cards allow connection and recording from just about any video device, such as cameras, Video Cassette Recorders (VSRs) etc. The software adjusts the size of the movie frame, compression, frame rate, and many other options to compensate for the user's system delivery speed limitations.
Real Networks, produces the software, that I use. I find their file format (RA or RN), to be efficiently compressed producing fine quality sound and video clips that I can use in an e-mail message for streaming across a network or the Internet. Their software allows direct capture from a capture card or you can import just about any other file type such as AVI or MOV. On the down side, once the data is converted (encoded) to a RA or RN file, you must use their software editors to make changes to the file. I found their editing tools could be better.
I recommend initially capturing your video to an AVI file format, either uncompressed or compressed using a codec, depending on your available storage space. I use Adobe Premiere, which features a wide range of special effects. After I complete movie development, I use Real Networks software to convert the AVI to the smaller and more efficient RA or RN movie file. Then I use this file for actual movie delivery (streaming). During conversion, the Real Networks software will encode the file so that it can automatically vary the output characteristics of the file depending on the actual speed of the connection. I retain the original AVI file for future editing requirements. If your Real Networks file requires changes, I make the changes to the original AVI and convert that file back to RA or RN format.
Rick Paquin is a member of the DON-IT Umbrella Program Team.