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Digital video technologies
1. Technical papers | Digital video technologies Digital video technologies This paper deals with consumer level digital video technologies. What is digital video? The term 'digital video' simply describes video recording, editing and playback technology that employs digital rather than analogue formats. In the same way, the term 'digital audio' is used for recording and playback technologies (such as audio CDs or digital audiotape) that employ digital as opposed to older analogue formats. The acronym ‘DV’ is commonly used in a variety of different ways. Firstly, DV refers to the compression format (DV25) employed to capture, edit and store video footage. DV is also applied to cameras that record using mini-DV tape, compressing footage using the DV25 standard. Finally, DV is used much more generally, to encompass the digital video concept as a whole. The advantages of digital video over analogue are similar to those offered by digital audio technologies. Digital video footage can be viewed, edited and – copyright restrictions permitting – copied almost endlessly with no loss of quality. Features such as music, titles and special effects are easy to add. By contrast, analogue video production and editing technologies are much more complex, requiring professional expertise to achieve competent results. Digital video can be distributed by various media such as the internet, DVD/CDs and 3G mobile networks. In a digital video camera, digitisation and compression of the video signal takes place in the camera as the footage is filmed. Provided that the computer on which editing is to take place is equipped with a suitable port, digital video footage can be downloaded swiftly and easily from the camera to the computer. An alternative way of producing digital video is to use an analogue video camera plus a personal computer equipped with a video capture card. In this case the digitisation process takes place within the computer rather than the camera. The ports and cables that support the direct transfer of digital video files between devices are commonly based on the Institute of Electrical and Electronics Engineers (IEEE) 1394 standard, often known as Firewire or, in the case of Sony equipment, i.LINK. FireWire provides a single plug-and- socket connection to which up to 63 devices can be attached with data transfer speeds of up to 400Mbps (megabits per second). Significantly faster than most other data transfer technologies, this allows the swift and simple transfer of very large digital video files between devices. Why has digital video become a mainstream technology? The rise of digital video is the result of a combination of factors. Continued developments in computer processing speeds mean that many consumer-targeted personal computers are now powerful enough to run digital video editing software. Such software enables users to work with digital video files on their desktops, running video-editing applications on the same machine that they use for other tasks such as word processing or web browsing. DV offers appreciably better quality video than consumer analogue solutions. Also, the inclusion of FireWire ports on DV cameras and many computers, coupled with the widespread availability of add-in low-cost FireWire PC cards, means that it is now much faster and easier to transfer video to a computer. At the same time, prices of digital video cameras have dropped considerably. Consumer digital video cameras (also referred to as digital camcorders) enable users to produce high-quality video footage at relatively low cost – a system comprising a digital video camera and an appropriate computer for video editing can now be purchased for less than £1200. These systems provide functionality comparable with the type of video editing hardware and systems that until recently were used only by © Becta 2004 http://www.becta.org.uk page 1 of 18 updated April 2004
Becta | Technical paper | Digital video technologies professionals. Users can produce excellent results without high levels of technical expertise and expenditure. Software and operating systems have also embraced digital video. Apple's iMovie and the inclusion of Movie Maker in Windows ME and XP are indicative of the fact that digital video has made the transition from the professional to the mainstream consumer market and is now an established easy to use technology. Faster computers, broadband connections and inexpensive storage have all helped to fuel demand for digital video. © Becta 2004 http://www.becta.org.uk page 2 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Working with digital video When starting out, the first aspect to consider is the technology necessary to capture digital video footage. You will need either a digital video camera, or an analogue camera and an analogue-to- digital capture system. The second aspect is the digital video editing process, which is carried out once the digital video files have been downloaded to a suitably specified computer. The main issue here is choosing appropriate video editing software. Finally, you will need to consider video delivery solutions. How will audiences view the video footage? Which digital video formats to use? Will the footage be streamed across a local area network or made available across the internet, or both? These three areas are discussed in more detail below. 1 Digital video capture: cards and cameras While both analogue and digital equipment can be used for digital video capture, analogue video cameras require a means to convert analogue footage to digital to allow it to be downloaded to and edited on a computer. Digital video cameras digitise video footage as it is filmed, which avoids the need for further conversion. For how to choose digital video cameras see: www.ictadvice.org.uk and Becta publications using digital video in teaching and learning (booklet/cd-rom). Analogue equipment Analogue camcorders and VCRs are still available and are very widely used. Analogue video equipment can be used in combination with digital video capture devices that convert the analogue video signal into a digital format that is stored and edited on a computer. Such capture devices range from low-resolution USB (universal serial bus) devices, primarily aimed at the home user and costing £40–£200, to more powerful systems aimed at the semi-professional. The devices can convert to digital formats the signals from a variety of analogue video sources, such as VHS videotape or a live feed from a camera or television. Most capture devices designed for use with analogue video are based on expansion cards that are installed in the computer. However, external devices that can be installed simply by plugging them into a computer's USB port are also available. Digital equipment It is becoming accepted that the future of video camera technology is digital. Some digital still cameras can capture short video clips, but compared with digital video cameras their performance and functionality are limited. There are several digital video camera formats – at present there is by far the widest choice of video camera in the mini-DV and Digital8 categories. Mini-DV and Digital8 record in digital video format onto cassette tape. There are a wide variety of cameras of different quality and price to suit the needs of various users. Mini-DV Mini-DV (originally known as digital videocassette or DVC) uses mini-DV cassettes to record up to an hour of very high quality digital video. The type of compression employed by DV greatly simplifies access and editing operations. Mini-DV cameras tend to be smaller than their Digital8 or disc-based counterparts. Most consumer-targeted mini-DV cameras currently tend to fall in the £400–£1500 price range, depending on features and specification. Digital8 Digital8, which is a proprietary Sony format, records video using DV compression onto Video8 or Hi-8 tapes that run at twice their normal speed in NTSC systems and at one-and-a-half times in PAL systems. NTSC is the system for TV broadcast and reception in the USA, while PAL is the system used in the UK. When used for digital video recording, Video8 or Hi-8 tapes thus hold half or two-thirds the time shown on the label. Digital8 cameras can also play back 8mm and Hi-8 analogue recordings over IEEE 1394 connections, allowing these recordings to be read into desktop video-editing applications on a computer fitted with an appropriate capture device. Due to © Becta 2004 http://www.becta.org.uk page 3 of 18 updated April 2004
Becta | Technical paper | Digital video technologies its backwards compatibility Digital8 is a good solution for users who already have a collection of 8mm/Hi-8 recordings. Other formats MicroMV is a newer format developed by Sony. The tape is 70per cent of the size of a DV tape resulting in smaller size cameras and delivers 60 minutes of digital video. Recordings are made in MPEG-2 format. DVD-RAM/DVD-R/-RW camcorders record in MPEG-2 format onto 8cm optical discs allowing 30 minutes of high quality or 60 minutes of lower quality footage to be stored on one disk They are more expensive than their miniDV counterparts as is the media. The convenience of recording to optical media which can be played in computer drives/DVD players will suit some users. They allow random access to disc contents and may be more durable than tapes. However, there are issues with the ease of editing of the MPEG2 format used by these cameras and working with MPEG2 encoding requires a powerful computer. Hard disk Hard disk units are available for some DV cameras. This is a professional feature at present but may become more common. It is also possible to record directly to computer hard drives with a Firewire connection and appropriate software. Flash memory (tapeless camcorders) Cameras recording to flash memory (card or internal) have become more common. Internal flash memory is usually small capacity and will only record a few minutes of video. These cameras usually record in mpeg formats (see: digital video encoding formats).There are two main types of these cameras: i) Inexpensive models suitable for taking short video clips such as Digital Blue Digital Movie Creator. There is an increasing range of compact digital video cameras and multifunction devices capable of recording low quality video suitable for inserting in presentations and email. ii) A new range of high quality, very compact digital video cameras with quality optics and LCD screens. These cameras record in MPEG2 and/or MPEG4 but do not yet compare with the quality of DV. Some of them offer up to 3 megapixel still photography. Compared to DV cameras these devices are expensive and of limited capability. They currently sell on their size and convenience. As the capacity and transfer rates of flash memory increases and prices fall these kinds of camera may become more prevalent. Many miniDV cameras also include a flash memory card for recording still photos and mpeg4 video clips. High definition video This high resolution 16:9 ratio, progressive scan format can now be recorded to standard miniDV cassettes (see: future trends). Consumer high definition cameras are becoming available but this is currently an expensive, niche market. It is also possible to capture video using inexpensive webcams. These normally connect to a computer via USB. While they are much cheaper than DV cameras, webcams offer lower quality and less flexibility for editing purposes, as they do not capture video in DV format. Digital video is available on many portable devices from digital stills cameras to mobile phones. This is contributing to the emergence of digital video as a standard technology used and shared by people on a daily basis. Other equipment There is a vast array of equipment and accessories associated with digital video. However, four key pieces of equipment need to be considered. © Becta 2004 http://www.becta.org.uk page 4 of 18 updated April 2004
Becta | Technical paper | Digital video technologies 1) Microphone: DV cameras have built in microphones which do not deliver the best sound recording. An external microphone is a valuable addition, particularly for recording dialogue. It will also eliminate the recording of operator noise. 2) Tripod: an invaluable aid to producing smooth, steady shots. 3) Lighting: additional lighting is useful to produce good results especially indoors. 4) Batteries: The lithium-ion battery packs supplied with cameras usually have a small capacity. A second backup battery is essential to ensure uninterrupted shooting. It is also possible to buy larger battery packs providing much longer usage. Using the viewfinder rather than the LCD screen saves power. For further information see the hardware section of the Becta CD-ROM Teaching and Learning using Digital Video. Digital video transfer The IEEE 1394 standard has been adopted by the consumer electronics industry as the primary method of connecting digital video cameras to computers. It is an excellent interface technology for high-bandwidth applications such as digital video. Most Apple computers are supplied with six-pin FireWire ports – Apple's trademarked implementation of the IEEE 1394 standard. Sony's Vaio range of desktop and portable PCs include IEEE 1394 connections as standard in the form of four- and six- pin i.LINK ports – Sony's trademark for its implementation of IEEE 1394. IEEE 1394 connectivity is becoming increasingly common, especially on higher specification computers, but is not a standard feature. However, third-party IEEE 1394 interface cards that, when used with video editing software, convert PCs into powerful video editing systems are now widely and cheaply available. In May 2002 the 1394 Trade Association and Apple announced a no-fee licence agreement allowing the adoption of the FireWire trademark, logo and symbol as a brand identity for the IEEE 1394 connection standard. The agreement allows the FireWire trademark, logo and symbol to be used on products and packaging to promote IEEE 1394 compliance. While the name FireWire has become widely known in the USA and Europe, the term i.LINK has caught on in other areas, particularly Japan. A new version of FireWire, known as 1394b offering a data rate of 800Mbps is also available, but there are few consumer products yet available. It can carry data over longer distances, using fibre- optic cables as well as traditional copper wiring. 1394b is backwards compatible with 1394a. The Open Host Controller Interface (OHCI) specification is an open standard that allows FireWire cards to communicate with compliant operating systems, drivers, applications and devices. It is advisable to buy an OHCI compliant card to ensure compatibility with a wide range of software. An important consideration when choosing a digital video camera is whether it supports 'DV-in' as well as 'DV-out' via the FireWire port. Lower-priced cameras tend to offer DV-out but not DV-in. This is because camcorders with DV-in enabled incur a higher rate of import duty, hence the price differential between camcorders with DV-in/-out and DV-out only. DV-in is an important consideration, as it allows the recording of edited footage back to the camera from a computer for storage or distribution. Devices and modifications are available that enable DV input on cameras with DV-out only although these can invalidate the warranty. Many DV cameras include a standard USB connection but this is only intended for downloading stills or video clips from flash memory. Most desktop and portable computers now include a number of USB 2.0 ports as standard. USB 2.0 connections offer nominally higher data rates than FireWire (480Mbps as opposed to 400Mbps), but in practice its sustained throughput rates are usually lower than Firewire making it less suitable for DV capture. This is one reason why DV camcorders have continued to use Firewire connections. However, some devices that record in MPEG formats, such as DVD and tapeless camcorders, are employing USB2 connections to transfer these more compressed © Becta 2004 http://www.becta.org.uk page 5 of 18 updated April 2004
Becta | Technical paper | Digital video technologies video formats. It is perfectly feasible and becoming more common to have both USB2 and Firewire connections on computers. For the foreseeable future miniDV cameras should continue to use Firewire but other format cameras may increasingly use USB2. Using digital video cameras for still photography Many digital video cameras also allow the capture of digital stills as well as digital video. Until recently, maximum resolutions for still images taken using a video camera tended to be low. Consumer camcorders now offer up to 3 megapixels resolution which is equivalent to that of entry- level digital stills cameras. However, 1 megapixels or less is more common and overall stills quality cannot compete with dedicated cameras. Digital video cameras have additional benefits in that they generally include more powerful optical zooms than digital still cameras (typically 10x or more, as opposed to 3x on still cameras). For casual use, digital video cameras should provide adequate results when used for stills. Many video editing suites also allow the capture of stills from the video footage. This is called frame grabbing. The success of frame grabbing depends on the capabilities of your camera and software as the frame will often need to be deinterlaced. For more information, see the briefing paper on digital still cameras [http://www.becta.org.uk/technicalpapers]. Audio DV cameras use Pulse Code Modulation (PCM) to capture stereo sound in either 12bit or 16bit quality with frequency sampling rates of 32 KHz or 48 KHz (CDs sample at 44.1 KHz). It is generally recommended to capture at the highest quality. © Becta 2004 http://www.becta.org.uk page 6 of 18 updated April 2004
Becta | Technical paper | Digital video technologies 2 Video Editing Computer specifications Most modern computers are capable of handling digital video editing. However, when working with large video files, sophisticated editing software and adding effects, a powerful computer is beneficial. Minimum specifications quoted by manufacturers will allow the software and hardware to run but for smooth, fast, editing and output higher specifications should be considered. Processors: Pentium III 800Mhz (or equivalent) or Apple Mac G3+ 300Mhz are minimum specifications quoted by many editing software companies however it is advisable to use faster processors and some real-time hardware rendering cards(see below) require Pentium 4 2GHz+(or equivalent). Memory: 256MB should be regarded as a minimum but 512MB would be advisable. Serious video users should consider 1GB of fast memory. Hard disks: There are two main factors to consider: capacity and speed Capacity: Digital video requires large amounts of storage. One hour of DV takes about 13GB. It is important to remember that creating a 30 minute film may involve several hours of unedited footage. In addition, storage capacity for finished projects needs to be considered. Speed: When capturing video from the camera and working with video files a sustained throughput of data is needed. Hard drives need to sustain transfer rates over 3.6MB/sec. This will avoid dropped frames when capturing video. A fast (Ultra ATA or SATA) hard drive of at least 7200rpm is therefore recommended; ideally even faster SCSI drives would be used. It is also advisable to have a separate hard drive dedicated to video capture (some cards/software insist on it). This allows the drive to be formatted before each capture to ensure adequate performance and prevents problems caused by the operating system accessing the drive during capture. Graphics and Audio: Most Windows software packages now state that they require DirectX 9 compatible graphics and sound. Some packages require dedicated 3D accelerator cards. Operating systems: The latest versions of editing suites recommend Windows 98SE or newer (XP recommended) and Mac OS X (10.2.6). Video capture: A Firewire port or card (for miniDV cameras) or a capture card (for analogue cameras) is also required (see: 1 Digital video capture: cards and cameras). Video editing Once digital video footage has been transferred to a computer, it will usually require editing to convert the rough footage into a coherent final version. Digital video editing applications are non-linear – they allow the user to work flexibly, editing footage in any order. (In traditional linear editing, scenes have to be edited in chronological sequence.) While video editing has become much more accessible to computer users, it still depends to a large degree on the creative ability and skill of the user to manipulate multiple audio and video clips and use the various editing and special-effects tools. Digital video editing applications vary enormously in terms of features and interface design. Some are aimed at complete beginners and are consequently designed primarily for ease of use. Examples include Movie Maker, a video editor supplied as a standard feature in Windows ME and XP, and Apple's entry-level iMovie editor. Others, such as Adobe's Premiere, are aimed at experienced users and provide advanced features, including special-effects filters, text tools and audio-editing controls, but are more complicated to use. Prices of editing packages vary – the most basic are bundled with operating systems, while more advanced packages can cost in excess of £500. Editing software is often bundled with Firewire/video capture cards and cameras. © Becta 2004 http://www.becta.org.uk page 7 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Most digital video editing software packages support a range of file-output formats suited to different purposes. Other software packages, such as QuickTime Pro, provide file-format conversion facilities, amongst other functionality. Rendering Rendering is the processing of changes, transitions, effects, titling etc. created during the editing process before outputting to tape or video file. This requires a great deal of processing power. On less expensive solutions this is done by the software (using the computer’s processor) and takes a considerable amount of time to accomplish. The time taken will depend on the speed of your computer and the amount of rendering needed. This delay in seeing the results of editing and waiting for video to be prepared for output can be frustrating. For faster results it is possible to buy hardware video card solutions which allow ‘real-time’ rendering. These cards let the user apply transitions etc and immediately and see the results in full quality. They are often sold complete with high-end editing software and provide semi-professional features. At around £500 these cards offer good value as the bundled software often costs around the same on its own. The time saved is also invaluable and encourages experimentation. Some newer editing software suites emulate real time rendering by continually processing in the background. This relies on fast processors and large amounts of memory. Real time cards can also speed up capture of video and compilation/encoding (compression) for output. Encoding video on a standard PC can be extremely time consuming. The added speed real- time cards offer can increase productivity considerably. Digital video encoding formats Compression is the reduction in size of data in order to save space or transmission time. Digital video formats use compression to reduce the size and data rates of video files while keeping the image quality as high as possible. The fact that a minute of uncompressed video requires around 1.5GB of storage illustrates the importance of compression when working with digital video. An extremely fast and expensive disk array, capable of storing and delivering huge amounts of data to the computer's processor very rapidly, would be necessary to work with and edit uncompressed digital video footage. Digital video is compressed with various compression algorithms known as codecs (compression/decompression) which define how video is compressed and decompressed by the computer. Different types of compression are suited to different purposes and consequently have different advantages and disadvantages. It is important to check that the types of compression employed by the digital video recording equipment and format you choose are appropriate for your needs. A useful distinction is between formats that are appropriate for capturing and editing processes (such as DV) and formats that are better suited to output and storage (such as, QuickTime or Windows Media). DV DV is the highest-quality, most cost-effective consumer video format yet made generally available for filming and editing purposes and is currently the most widely used digital video capture format. DV PAL captures video at a 720x576 resolution at 25 frames per second, stored at a bit rate of 25Mbps. DV25 compression (5:1) offers high quality video but still has significant storage requirements: one hour of DV footage requires about 13GB of storage. AVI AVI, Audio Video Interleave was originally developed for Video for Windows and is actually a container format for several compression codecs and therefore supports various different levels of quality. DV is captured onto a computer in DV AVI type 1 or 2 depending on your software configuration. Apple Macintosh computers usually capture in uncompressed .mov format. © Becta 2004 http://www.becta.org.uk page 8 of 18 updated April 2004
Becta | Technical paper | Digital video technologies MPEG MPEG, the Moving Picture Experts Group, overseen by the International Standards Organisation (ISO), develops standards for digital video and digital audio compression. MPEG-1 with a default resolution of 352x240 was designed specifically for Video-CD and CD-i media and is often used in CD-ROMs. MPEG-1 audio layer-3 (MP3) compression evolved from early MPEG work. MPEG1 is an established, medium quality format (similar to VHS) supported by all players and platforms. Although not the best quality it will work well on older specification machines. MPEG-2 compression (as used for DVD movies and digital television set-top boxes) is an excellent format for distributing video, as it offers high quality and smaller file sizes than DV. Due to the way it compresses video MPEG-2-encoded footage is more problematic to edit than DV footage. Despite this, MPEG2 is becoming more common as a capture format. MPEG 2 uses variable bitrates allowing frames to be encoded with more or less data depending on their contents. Most editing software now supports MPEG2 editing. Editing and encoding MPEG2 requires more processing power than DV and should be done on well specified machines. It is not suitable for internet delivery. MPEG-4 is a set of video and audio standards intended to deliver quality video over limited bandwidths that also support a range of other media types such as text, still image and animation. MPEG-4 offers high-quality, scaleable streaming over a range of bandwidths, including those provided by mobile networks. The standards also include components and elements that allow the viewer to interact with the picture on the screen or to manipulate individual elements in real time. The MPEG4 format is a container for various versions called layers. There are different implementations, some of which are proprietary and not compliant with the ISO MPEG4 standard. It was initially thought that MPEG4 would become the default format for video over the internet. With support from Apple, Real Networks and others this may still be the case. However, problems over licensing costs and the lack of digital rights management in the standard made many content providers slow to embrace it. These issues are being tackled but it also faces competition from proprietary formats such as Windows Media. MPEG4 is beginning to be supported in other areas such as mobile video (3G), mobile television, set-top boxes and video on demand (VoD). Advanced Video Coding (AVC) This is an emerging video codec jointly developed by ISO and ITU (International Telecommunications Union) and also known as MPEG4 part 10 and H.264. It promises extremely efficient compression and good quality video at half the bitrates of current MPEG4. It is starting to be adopted by broadcasters and mobile operators for future systems. It may eventually replace MPEG2. Realvideo A proprietary format from Real Networks. Designed for distributing video on the internet (limited bandwidth) with high compression. It supports scaleable downloads and streaming. It can only be played by Real Player applications. A Real Video encoder can be downloaded for free and offers reasonably fast encoding for low-bandwidth video. Windows Media Video WMV9 is the latest version of Microsoft’s proprietary video encoder. It offers good quality at various bitrates. It is beginning to be supported by consumer electronic devices. It supports streaming and downloads. Microsoft also has Advanced Streaming Format (.asf) specifically for streaming media. This container format supports various codecs. A free WMV encoder is available. Encoding WMV is slow. © Becta 2004 http://www.becta.org.uk page 9 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Quicktime The latest versions of Apple’s QuickTime support standard MPEG4 compression and codecs such as Sorenson3. It supports streaming and progressive downloads. QuickTime files can be played on Apple Macintosh and Windows computers (with appropriate player). An upgrade called Quicktime Pro allows encoding in these codecs. It is a relatively fast encoder. DivX A relatively new video format/codec designed for downloading high quality, full-length movies over broadband connections. It originally used a non ISO (International standards Organisation) compliant version of MPEG4 but the newer versions are compliant. DivX files can be played with a DivX player on all platforms or in Windows Media Player/QuickTime player. A free encoder is available. Encoding DivX files takes time but offers high quality. ExtremeTech recently tested and compared some popular video codecs: http://www.extremetech.com/print_article/0,1583,a=121163,00.asp As digital video becomes more widespread across a range of applications it remains to be seen whether a single codec such as MPEG4 will be adopted or if different devices will offer different proprietary solutions. Ultimately, multiple codec support may be the solution. © Becta 2004 http://www.becta.org.uk page 10 of 18 updated April 2004
Becta | Technical paper | Digital video technologies 3 Delivery solutions There are a variety of ways to make digital video productions available. The key issue is to identify which distribution medium is the most appropriate for the video's intended purpose and audience. The final choice of delivery format and medium will depend on a range of factors, including cost, quality and cross-platform support. The main options include: • direct output or recording to analogue media • output to computer storage media • distribution over a network. Direct output or recording to analogue media There are two approaches here: output to conventional video-recording formats and displays, and viewing on the computer on which the footage is edited. Output to conventional video-recording formats and displays The most common way of presenting a video production through a conventional audio-visual set- up is via a television set. If the video production is to be presented elsewhere, it is usually recorded to VHS tape. Regardless of whether the video production is to be displayed directly on a television or transferred to VHS, the issues for digital video production are the same. If the digital footage is edited on a computer equipped with an appropriate video output (such as an S-Video or composite video output), a VCR or television can be directly connected to the computer to record or display the final edited footage. If the computer used for editing does not have such an output, an alternative approach would be to record the edited footage back onto the video camera. The camera can then be connected to a television or VCR for display or recording. However, this requires a camera that supports DV-in as well as DV-out (not a standard feature on all models). A cruder method is to connect a digital video camera directly to a VCR or television immediately after the footage has been shot. Obviously this means that little or no editing of the footage is possible prior to recording or display. It should be remembered that while DV can be copied and recopied digitally without degradation, copying it to a lower resolution analogue format such as VHS will result in a loss of quality. Video copied from analogue to analogue degrades with each copy. Viewing on the computer on which the footage is edited and hard disk solutions This is the simplest option for playback but it is much more restrictive than other delivery options. Using a portable computer for editing can provide flexibility and mobility. It can be easily transported between locations and can also be connected to a data projector for display to larger audiences. Edited video footage is kept on the computer's hard drive. As the video files – even in compressed formats – can be very large, it is important to ensure that sufficient storage capacity is available. The price of hard disk storage has fallen significantly over the last few years. This makes it more economic to archive video projects onto large capacity hard drives. Portable hard drives offer a degree of mobility but need to be connected to a computer for video playback. Recently mobile multimedia players have become available which are hard disk based devices with in-built screens. These are relatively expensive at present but many new versions are due in 2004 and prices should fall. Output to computer storage media Currently, the most readily available removable computer storage media of sufficient capacity to accommodate digital video are writable and rewritable CD and DVD. To transfer video to these formats, the computer used for editing needs to be equipped with a writable CD or DVD drive and accompanying software. CD offers up to 700MB of storage while DVD offers 4.7GB (dual layer 8.5 GB discs/drives should become available this year). Writing to CD or DVD provides flexibility in that the final edited video footage can be played on any computer that has the appropriate drive and video player software installed; it may also be possible to play discs on consumer DVD players. CD-Rs can © Becta 2004 http://www.becta.org.uk page 11 of 18 updated April 2004
Becta | Technical paper | Digital video technologies be bought in bulk very inexpensively. DVD media is currently more expensive but the extra storage they provide allows for an hour of high quality video (720x576) to be recorded. While CD-R (recordable CD, once-only) and CD-RW (rewritable CD) standards and media have matured, there are a number of different recordable and rewritable DVD standards. You should check that any DVD formats you consider are compatible with any other DVD equipment you wish to use. However, even using compatible formats does not guarantee that a disc will work on a particular player. Recordable DVDs and DVD drives/players are only 85% compatible according to research carried out by NIST and the Optical Storage Technology Association: http://www.nist.gov/public_affairs/techbeat/tb2003_1204.htm#tests. Some manufacturers publish compatibility details for drives, players and discs on their websites. For example, HP has also published a list of DVD players and DVD-ROM drives compatible with DVD+RW and DVD+R discs created using HP's DVD+RW drive [http://www.hp.com/support/dvd- compatibility]. For more information on these formats, see Becta's advice on removable storage media [http://www.becta.org.uk/technicalpapers]. CD-based video formats Computer CD-ROM drives will play back footage written to recordable CDs as files (where video footage is written to the recordable CD as, for example, a QuickTime file, in the same way as a Word file might be written to other recordable media such as a floppy disk). Specific CD-based formats for video include VCD and SVCD. VCD (also called video CD) uses MPEG-1 video at a resolution of 320x200 pixels on CD media. VCD offers quality similar to that of VHS tape, far short of DVD. A VCD disc holds around 70 minutes of video. VCDs can be played in many consumer DVD players and computers equipped with a DVD-ROM or CD-ROM drive and a software-based decoder/player. SVCD (also called super video CD) is very similar to VCD. SVCD has the capacity to hold about 20 minutes of high-quality MPEG-2 video, offering significantly better quality than VCD. VCDs and SVCDs can be played on some consumer DVD players and on computers equipped with a DVD-ROM or CD-ROM drive and a software-based decoder/player. It is also possible to use menus and chapters, as used on DVDs, VCDs and SVCDs. Some DVD authoring packages (such as Sonic's DVDit!) allow the necessary player to be written to the CD along with the video footage. This enables computers that do not have the necessary player/decoder software installed to play the disc, which then plays back automatically when inserted in the drive. DVD-based video formats As with CDs, computer DVD-ROM drives will play back footage written to recordable DVD discs as files. If you intend to play back the DVDs you create on consumer DVD players, DVD authoring packages such as Apple's iDVD and Pinnacle's Impression DVD-Pro allow you to create menu structures for your edited video footage that can be accessed using a consumer DVD player's remote control. Many video-editing packages also include DVD authoring facilities. Many current consumer DVD players will play back DVDs authored using such packages and recorded in one or more of the various recordable DVD formats. © Becta 2004 http://www.becta.org.uk page 12 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Distribution over a network There are essentially two ways of serving video across a network, whether a local area network or the internet: file download and streaming. File download This is the simplest approach – before playback the entire video file is downloaded across the network to the client machine. This approach is most suitable for relatively small video files. The video quality is guaranteed and the only constraint is the time taken to download the file which will depend on the connection. Streaming Different versions of a video clip may be appropriate for streaming to different audiences. For example, in the case of streaming video from a website, a highly compressed version that displays at a resolution of 160x120 would be appropriate if the clip is most likely to be viewed by users across a 56Kbps modem connection. A higher-quality 320x240 version would be more appropriate for users with broadband internet access. There are two main types of streaming: a) Progressive downloads Although not technically streaming, progressive downloads achieve a similar effect. The whole file is downloaded to the computer but the video will begin to play before this process is complete. This is also known as pseudo-streaming. This kind of progressive download will work from a standard http web server. The ability to have smooth, uninterrupted playback before the file has been completely downloaded is dependent on the quality and speed of the connection and size of the file downloaded. This is a good, inexpensive solution for relatively short video clips. b) Streaming The second approach is streaming where, once requested by the user, the video file is sent in a continuous stream to the client computer and is played as it arrives. The file is not copied to the client machine thereby providing copyright protection. This option is more complex and expensive but it is more effective when delivering video to very large audiences. Real-time streaming video requires a different architecture. It involves a dedicated server application such as Microsoft's Windows Media Server, Apple's QuickTime Streaming Server (available for both Mac and PC platforms) or RealNetworks' Helix Server range connecting to a client application (media player). The connection between client and server allows some degree of interactivity. Some servers can detect the connection speed of a user and adjust the video stream accordingly. Users are also able to skip ahead to the desired section of a video. An alternative method is playing back a video in the browser with a downloaded Java applet. This creates a seamless experience and obviates the need to encode video for different media players. Streaming video is blocked by some firewall configurations. Streaming depends on the quality of connection more than progressive/downloads as the file is not downloaded for later viewing. Also Real Time Transfer protocol (used for streaming media) does not have error correction so any lost or corrupted data is not recovered. This characteristic helps to keep a stream moving but can result in ‘choppy’ video. If it is known in advance that video is intended to be streamed this should be taken into consideration when shooting and editing. Video with static backgrounds, limited detail and without fast movement works best for streaming. © Becta 2004 http://www.becta.org.uk page 13 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Streaming video is continuing to grow in importance as digital video production technology, broadband and mobile connectivity become ever more widely available. For more information on using streaming in education and what is required see the guide published at: http://www.clickandgovideo.ac.uk/. Choosing a video output format Whether your video is to be viewed on a local area network or accessed via the internet (or both) will have an impact on the video output formats you employ. • If users will view the video on a local area network and will employ the same player software (as is likely if client software configurations are managed and controlled centrally), the output of the final edited footage can be in one file format that can be read by everybody. Player software is freely available from a variety of sources including Apple, Microsoft and Real Networks. It is important to bear in mind the considerable additional burdens that viewing large video files over a local area network will place on network infrastructure and performance. • For delivery from a website, it is important to choose an output file format that has good cross-platform support or to provide video in multiple file formats, to ensure that as many people as possible are able to play it. It is vital to consider the connection speeds of your users. Providing files with different amounts of compression for dialup and broadband users could also be useful. Some streaming solutions can automatically detect a user’s bandwidth and send an appropriate size file. Specialist software such as Media Cleaner is available to optimise video for Internet delivery; however, many editing packages provide this facility. The upgrade versions of QuickTime, Windows Media and Realplayer allow encoding in these formats as do many video editing packages. Video formats It is difficult to give definitive advice on which format to choose as this will depend on individual situations. It is necessary to balance the required video quality to the amount of compression needed for the chosen distribution method. This may involve some trial and error. See video encoding formats (above) for an explanation of different formats and codecs. This site contains more information on different video codecs: http://www.discreet.com/support/codec/ Media Players There are several media players most of which have basic versions freely available to download or which come as part of the operating system. It is possible to install more than one player. The three most common players are discussed below. Open source, cross-platform players such as Videolan’s VLC are also available. Realplayer Real Networks have decided to support all major video formats in their latest players. However, in order to play certain formats such as QuickTime or WMV the codecs will need to be installed separately. Essentially this means having QuickTime player and Windows Media Player on your computer. Realplayer is available for Windows, Apple Macintosh and Linux systems. Realplayer has been adopted by some mobile phone networks for mobile video. QuickTime Player Apple’s QuickTime Player also has a Windows version available. It supports MPEG1, MPEG4, DV, AVI, MPEG2 (with a plug-in) and Flash. © Becta 2004 http://www.becta.org.uk page 14 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Windows Media Player Supports all Windows Media files, AVI, MPEG2 (with DVD decoder installed), Flash Future trends High definition/progressive scan High definition is widely seen as the next major development in television (HDTV), film and video. Progressive scan, where the frames are scanned in a single pass instead of being made from two interlaced fields is also emerging on cameras. High definition video increases the resolution, is shot and distributed in widescreen and has better colour and sound. High definition video cameras have been used commercially for some time. A new consumer format called HDV has been developed by Canon, Sharp, Sony and JVC and allows high definition video to be recorded onto standard miniDV tapes. It has also been supported by editing software companies such as Adobe and Ulead. HDV is recorded using MPEG2 Transport Stream compression in the 16:9 aspect ratio. High definition is an emerging technology at the consumer level with certain limitations on performance and ease of editing. It is not yet available in the UK. The UK, (which is far behind the USA and Japan in the deployment of HDTV), is seeing the emergence of progressive scan 16:9 wide-screen capable cameras which also record in MPEG 2 to miniDV tapes. These are designed to be played back on widescreen displays but can scale to standard 4:3. High capacity optical discs High capacity optical discs are beginning to emerge with several different standards such as bluray and HD-DVD. These discs are higher density and can hold between 18GB and 50GB. They can only be used on dedicated players/drives. This technology is still in development and is not yet available in the UK but may eventually replace DVD. Computer processor speeds and memory are increasing all the time. As a result, the range and complexity of tasks that computers are capable of handling will continue to increase and diversify. The transition that digital video technologies have made to the desktop is clear evidence of this trend and digital video capabilities on consumer-oriented computers are likely to become increasingly commonplace. The consumer digital video market is also predicted to continue to grow, reflecting the rapid development of other digital consumer products and markets, such as digital still cameras, mobile phones, DVD players and digital TV. The digital video camera marketplace is very competitive so prices will continue to fall, and functionality and quality will improve. Mini-DV is currently the most widely available format and it remains to be seen whether other digital video camera formats will reach the same levels of acceptance and penetration. However, it should be noted that this situation does not mirror the rivalry between VHS and Betamax video formats of 20 years ago – the output and distribution formats for digital video are essentially independent of the original recording format. It remains to be seen whether a particular video codec achieves dominance in digital video distribution. In the future as broadband connections become commonplace and more mobile phones and other devices have video capabilities built in, people will become more accustomed to working in the medium of video. Strategy Analytics1 predict that the mobile video market will be worth $4.7 billion by 2008 with 150 million users accessing video clips. In addition to video authoring and editing software, subject-specific applications based on digital video are also available. For example, in the field of sports science and biomechanics, packages such as 1 http://www.strategyanalytics.com/cgi-bin/greports.cgi?rid=152004010431 © Becta 2004 http://www.becta.org.uk page 15 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Game Breaker, Dartfish and Quintic allow complex manipulation of video footage for training and analysis purposes, allowing athletes to view, analyse and synchronise footage of their performance and compare it with that of contemporaries or professionals. Such packages could also be used in other ways, for example to investigate the laws of motion within the science curriculum. The range of applications harnessing digital video and the variety of topics in which digital video can be used to support teaching and learning are likely to increase as the technology continues to become both more affordable and more widely adopted. For more information on using digital video in learning and teaching see: www.ictadvice.org.uk and Becta publications using digital video in teaching and learning (booklet/cd-rom). Legal Safety issues When working with digital video it is vital to consider the school’s duty of care towards children. This is particularly important when distributing video. Permission should be obtained from parents and pupils should be unidentifiable (no names) so that they cannot be contacted. More information can be found at: http://safety.ngfl.gov.uk/schools/. © Becta 2004 http://www.becta.org.uk page 16 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Other sources of information Becta ICT Advice site http://www.ictadvice.org.uk Advice on using DV in teaching and learning and case studies Digital Video Awards http://www.becta.org.uk/digitalvideoawards A scheme for all UK students aged between 5 and 18. It celebrates excellence in creative use of digital video. Previous winners’ clips can be downloaded. What the research says about digital video in teaching and learning http://www.becta.org.uk/research/research.cfm?section=1&id=546 A summary of key research evidence on the use of DV and explanation of findings. Using digital video in teaching and learning (booklet and CD-ROM) Digital video forum mailto:email@example.com Digital Video Pilot [http://www.becta.org.uk/research/research.cfm?section=1&id=532] Contains information about the pilot scheme run by Becta and further information about the use of digital video. Becta commissioned the British Film Institute (BFI) to undertake an evaluation [http://www.becta.org.uk/page_documents/research/dvreport_241002.pdf] of the Digital Video Pilot Project. Useful links About.com: desktop video [http://desktopvideo.about.com/] Adam Wilt's DV pages [http://www.adamwilt.com/DV.html] Technical overview of DV formats and technology. Adobe DV Primer [http://www.adobe.com/motion/events/pdfs/dvprimer.pdf] An introduction to desktop digital video (PDF). Adobe Streaming Media Primer [http://www.adobe.com/products/aftereffects/pdfs/AdobeStr.pdf] An introduction to streaming media technologies and techniques (PDF). British Film Institute (BFI) [http://www.bfi.org.uk/] Includes a teachers' centre and offers resources and help for teachers of the moving image. Consumer DV Reviews [http://www.consumerdvreviews.com/] Detailed reviews of DV and DVD recording and production technologies, including cameras, DVD writers and digital video editing packages. DV Café [http://www.dvshop.ca/dvcafe.html] Links to many DV resources DVformat: [http://www.dvformat.com/] News, reviews articles Film Education [http://www.filmeducation.org/] Designed for primary and secondary teachers and students using film and new media across the curriculum. © Becta 2004 http://www.becta.org.uk page 17 of 18 updated April 2004
Becta | Technical paper | Digital video technologies Media Education Wales [http://www.mediaedwales.org.uk/] Non-profit company supporting media and moving image education in Wales with resources, training, projects, research and consultancy. MediaEd-The UK media and moving image education site [http://www.mediaed.org.uk] DV information and resources, including answers to frequently-asked questions about using digital video in the classroom. Moving images in the classroom [http://www.bfi.org.uk/education/teachers/classroom/miic/index.html] A teacher's guide to using moving images in the secondary school curriculum, by BFI Education. JISC Click and Go Video Project [http://www.clickandgovideo.ac.uk/] The Click and Go Project formally ended in August 2002, but resources are still available, including 'Video Streaming: A Guide for Educational Development' (PDF). Shortcourses: Digital Video [http://www.shortcourses.com/video/index.htm] The British Universities Film & Video Council (BUFVC) [http://www.bufvc.ac.uk/] Yahoo! Directory: digital video [http://uk.dir.yahoo.com/Computers_and_Internet/Multimedia/Digital_Video] IEEE 1394 Trade Association [http://www.1394ta.org/] Apple MPEG-4 information [http://www.apple.com/mpeg4/] MPEG Home Page [http://www.chiariglione.org/mpeg/] MPEG4 industry forum [http://www.m4if.org/] Advice on authoring VCDs, SVCDs and DVDs [http://www.dvdrhelp.com/] © Becta 2004 http://www.becta.org.uk page 18 of 18 updated April 2004
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