Developed and taught by Saimon Clark
Lecture
In this session you learn the background to, and basics of, digital video;
enough to use and create web video files, and critically evaluate the use of digital video in language studies.
Practical
You will acquaint yourself with a digital camcorder and VCR, and prepare to create a short video file.
The work for submission is to create a QuickTime video for inclusion on your web page; more details below.
Useful Links and Further Reading
Links
- PC Webopaedia – Video
- MPEG http://www.mpeg.org/
- iMovie HD Support
- BBC’s One Minute Movies Howto
- Videojug’s guides to How to Import Video in iMovie, How to Edit Video in iMovie and How to Edit Sound in iMovie
- BBC’s Film Network Guide
- FilmLondon’s Microwave guide to micro film making
- Longtail Community’s Overview of Audio and Video Transcoding and their Transcoding Best Practices
- British Universities Film and Video Council’s (BUFVC) Television and Radio Index for Learning and Teaching (TRILT) listings database of UK broadcasts
- BUFVC’s Copyright Site
- BUFVC’s Moving Image Gateway
Books
- Pogue, D. and Miller A. (2009) iMovie ‘09 and iDVD The Missing Manual, O’Reilly Media
- Chapman, N., and Chapman, J. (2000) Digital Multimedia, Wiley
Analogue Video
Video Pictures on television sets are made up of lines which fill the screen. Each line consists of a series of three electron-beam points, one each for the primary colours Red, Green and Blue, and the lines are fired across the screen one after another by electron guns within the Cathode Ray Tube. One screeenful of lines makes one picture; several pictures one after another become ‘moving’ pictures. For the brain to interpret the pictures on screen as continuous movement rather than a series of individually-displayed pictures, the pictures must be shown at a suitably high rate. This rate – the fusion frequency – is around 40 images (or frames) per second. Since 40 frames per second was originally considered to be too much for the equipment to handle, each frame was divided into two fields. One field had the odd-numbered lines, the other had the even-numbered lines. The two fields of each frame are displayed in quick succession, a process known as interlacing. In Europe, the standard rate is 50 fields – or 25 frames – per second, while in North America the standard is roughly 60 fields – or 30 frames – per second.
|
Standard |
Countries |
Frames /s |
Fields /s |
Lines |
|
|
PAL |
Phase Alternating Line |
W.Europe, China, Australia, New Zealand |
25 |
50 |
625 |
|
NTSC |
National Television Systems Committee |
N. America, Japan, Taiwan |
30 |
60 |
525 |
|
SECAM |
Séquential Coleur Avec Mémoire |
France |
25 |
50 |
625 |
Since a computer monitor automatically exceeds the required refresh rate, a different, more straightforward method of displaying video can be used; it is known as progressive scanning, and no interlacing is required. This means that video clips can use lower frame rates without falling below the fusion frequency. Analogue video can be represented in two forms, component and composite. This representation is to do with the way the different parts of the video signal are ordered and kept together. Component video is used to create and store professional-standard video footage, and is good at representing colour. Video is transmitted in composite form, which involves some data compression and consequently some loss of quality. The pictures received on a television set or stored on a household VHS video cassette are in composite form. S-VHS (and Hi-8) is a compromise between composite and component, and is often chosen when higher quality is required at a cheaper price than professional quality video. Other professional quality formats exist, but Betacam (or Betacam SP) has been a component video industry standard.
|
VHS |
composite |
|
S-VHS & Hi-8 |
S-video – composite/component |
|
Betacam |
component |
DV Digital Video
DV – Digital Video – is a digital data stream, made up of bits which combine to form pictures composed of pixels, in contrast to analogue signals which represent and stream the picture information in different ways. DV is replacing the analogue forms of video, but needs to be able work on existing television sets and equipment (PAL, NTSC, SECAM) as well as working to its own specifications.
MPEG standards – those devised by the international Moving Pictures Experts Group – are standards for the representation of digital video in various ways. MPEG-1 was the first agreed standard, and now MPEG-2 has achieved wide acceptance as a standard for digital television. Work continues on other related standards including MPEG-4. Digital camcorders and VCRs, which convert or play back images in digital video format are now standard in broadcasting and increasingly common for household equipment. MiniDV is now a high-quality small compact tape for digital camcorders and VCRs, and DVCAM is a broadcast-standard tape.
Computer-based Digital Video
Video digitized for use by a computer can start off in any of the forms mentioned so far, analogue or digital. To create computer-usable video, a card is required which can sample the video signal and process it into a form suitable for use and playback on a computer. These cards are often called capture cards, and the video signal is typically captured from a VCR or camera plugged into the card.
The term digital video can therefore be legitimately applied to
the DV formats used in video equipment or to the formats and file types related to computer use. Usually the context determines which sense is meant, but it helps to be aware of the distinction: in short, DV on miniDV tape isn’t the same as a computer file of video such as an AVI file. Essentially, the pictures which make up digital video of whatever sort are a series of bitmaps – computer images made up of pixels. Each picture of the size required for full-screen video is quite large in its own right: multiply the size of one full-screen picture by 25 to allow for the number of pictures required per second, then multiply that by 60 to allow for the number of pictures per minute, and very quickly the disk and memory space required to handle video efficiently mounts up. Chapman and Chapman estimate that normal PAL format video requires 31Mb per second, or 1.85Gb per minute: this means that the 10Gb hard drives of the CALL Facility machines can hold just over five minutes’ worth of normal-quality video. Transmitting it across the Internet would currently be more or less impossible. To reduce the size and strain of computer video, a number of strategies are used. The most obvious is to reduce the size: rather than being full-screen, the dimensions can be scaled down. Sometimes the resulting images are very small indeed, to the extent that it is dismissed as “postage stamp” video. The most significant strategy is compression – coding the information which makes up each image in a more compact way. The effects of compression adversely affect the quality of the video (in contrast to audio, where most compression techniques do not significantly diminish the quality of the original recording). The technical details of compression are vast, and the important thing at this stage is to know that they have to be applied and that the consequences can be severe.
Digital Video Production
Capture cards need to be compatible with the video equipment you are using. On a basic level, a normal household camcorder might have a yellow socket to give out video, and a red and white socket for the audio, and leads are used to connect to matching sockets in the computer card. VCRs sometimes have SCART plugs which output the same three leads to a capture card. A new standard lead for digital video is FireWire, a much smaller cable capable of high-speed data transmission. Capturing video can be a tricky and sometimes frustrating business, especially for the newcomer. The variables in the equation for success include the nature and capabilities of the capture card as well as the capture and editing software being used and (more mysteriously) its compatibility with the capture card. Informed trial and error in the early days is usually the best approach. If possible, capture uncompressed video according to the capture card’s default settings; then, using video editing software, resize and compress the sequence before exporting it is a computer video file. Capture the audio at a suitable level rather than raising or lowering it after capture. Once captured, video editing can be carried out using software such as Adobe Premiere, which has become something of a de facto standard (though other packages do exist). This program does on computer with digital video what used to be done for analogue video by large banks of machinery.
Analogue video editing is said to be linear – it involves physical playing and copying of video from one tape to another. Digital video editing is said to be non-linear – chunks of video can be copied or cut and moved around at random and almost instantaneously, speeding up the whole operation considerably.
An imperfect, but useful, analogy of the difference between linear analogue and non-linear digital video editing is the difference between writing with a typewriter and using a word processor. On a traditional typewriter, words have to be written in their final order, with the potential for correction limited to what can be achieved with Tipp-Ex, unless an entire sheet is thrown away and re-typed – which might upset subsequent pagination. In the latter case, corrections can be made anywhere, text can be composed in any order, without regard to pagination or layout. The ability to randomly access and change data, which is fundamental to the way we build computers, engenders these capabilities in text processing software, and analogous ones in video editing software.
Source: Chapman & Chapman
Once any required editing has been done, the footage can be prepared for ‘export’ to a file. It is at this stage that resizing and compression come into play. The context in which the video is to be used may determine the size. If it is to be used within software where other things are happening on screen than video playback alone, a smaller size may be an advantage (or at least less of a disadvantage); examples are the Italia 2000 and German Video Plus video-based software packages for language learning. If it is to be used for viewing as a broadcast programme would be viewed, in linear fashion, a larger window may be more appropriate if circumstances allow; an example is RealPlayer video files. A Codec is the general name applied to a compression technique. Codecs are used to reduce the amount of data in the resulting video file. For CD video, MPEG-1, Cinepak, and IntelIndeo were commonly used, but now other MPEG standards are coming in. On PCs, AVI files have been the standard format, and on Macs it’s MOV (QuickTime) files. Streaming video files, such as RealPlayer, QuickTime and now also Microsoft’s own version, where linear playback across the network is the prime objective, also use their own (sometimes proprietary) compression techniques. Many compression techniques for different purposes are covered by MPEG standards. For an illustration of how codecs are changing, compare the video files used in the Italia 2000 and German Video Plus packages: the latter was published in 2003, and uses a Microsoft version of the QuickTime-based MPEG-4 standard, while the former uses a codec called Cinepak. Finally, note that with the advent of firewire connections and programs like iMovie on the Mac, capture and manipulation of digital video is becoming more straightforward while still producing worthwhile output.
Video File Types and their use
|
.AVI |
Audio visual interleave |
Developed for Video for Windows; standard for PCs |
||
|
.QT |
QuickTime |
originally developed by Apple for sound and animation; now cross-platform, streaming, and used as the basis for MPEG-4 |
Cat Herders QuickTime clip embedded in a web page (QT4 plugin required from Apple QT Download). |
|
|
.RM |
RealPlayer/Real Media |
Cross platform files for streaming video |
étude de café (Ollie Wiseman) |
|
|
.MPEG .MPG |
Motion Pictures Experts Group |
Multi-platform files |
||
|
.SMIL |
Synchronised Multimedia Integration Language |
New web-based approach to multimedia programming based on XML; not a video format in itself |
Robert Pires interview Portuguese subtitles, From Umbro.com Live. |
For (another) full overview of video and other media sites, see the Kidon Media Links site.
- Compare and contrast the use of video in the Italia 2000 networked CD with the Italia 2000 web site or a Listening Comprehension site such as Que savez-vous sur la Francophonie?. How is video is used in each case? How well are the advantages of the computer integrated?
Practical/Work for Submission
Tasks
The emphasis in this assignment is collaboration to come up with a neat and effective clip. Assign tasks with the group, but agree and execute plans together. As well as allowing you some insight practical insight into using the camera, this work should also get you thinking about filming, visual narrative, lighting, production techniques and so on. Use the group’s Film Studies expertise, and consult the BBC’s One Minute Movies section for tips as well.
- Look at web sites designed with video for language study purposes, and explore them, such as the materials available on the Language Centre web site. Consider ways in which existing video-based resources could be adapted or created for use in your coursework, either for your own research of for teaching purposes.
- Use the BBC’s One Minute Movies site to plan and implement a film: the How To section neatly summarizes the things you need to think about
- Get familiar with the camcorder and work in groups to film a short sequence each. Get familiar with the connections between camera and computer, and learn how to use iMovie to capture your materials onto the computer. Plan a short film: script it, imagine camera shots, assign acting and camera roles. Film it. Explore iMovie, getting familiar with its basics, then digitize and edit the final product together. Create a web page which makes clear who has done what, includes a transcription, and a link to the film.
- Explore iMovie: learn how to do basic video editing. Explore the addition of effects, transitions and subtitles.
- When you’ve finished, export your movie for inclusion in your web site.
Book slots next week when you and your team can work on creating your individual video clips together, and when you can do your capture and editing using iMovie. Remember to keep the camera charged!
Film
- Film a short (30s-1 min) clip with words in one of your foreign languages, perhaps a few short phrases as an advert for the Faculty and Cambridge filmed in a good location.
By the start of your next workshop session, have short clips accessible from your site, plus a transcription of what is said during the clip (as ever in one of your languages, or concerning a suitable linguistic topic). The video clip doesn’t have to be an artistic or pedagogical masterpiece (though it might!) but it should certainly give you a feel for making a clip.
