Digital video is a type of video recording system that works by using a digital, rather than analog, representation of the video signal. This generic term is not to be confused with the name DV, which is a specific type of digital video. Digital video is most often recorded on tape, then distributed on optical discs, usually DVDs. There are exceptions, such as camcorders that record directly to DVDs, Digital8 camcorders which encode digital video on conventional analog tapes, and the most recent JVC Everio G camcorders which record digital video on hard disks.
The terms "camera", "video camera", and "camcorder" are used interchangeably in this article.
Introduction Video cameras come in two different image capture formats: interlaced and progressive scan. Interlaced cameras record the image in alternating sets of lines: the odd-numbered lines are scanned, and then the even-numbered lines are scanned, then the odd-numbered lines are scanned again, and so on. One set of odd or even lines is referred to as a "field", and a consecutive pairing of two fields of opposite parity is called a frame.
A progressive scanning digital video camera records each frame as distinct, with both fields being identical. Thus, interlaced video captures twice as many fields per second as progressive video does when both operate at the same number of frames per second. This is one of the reasons video has a "hyper-real" look, because it draws a different image 60 times per second, as opposed to film, which records 24 or 25 progressive frames per second.
Progressive scan camcorders such as the Panasonic DVX100 are generally more desirable because of the similarities they share with film. They both record frames progressively, which results in a crisper image. They can both shoot at 24 frames per second, which results in motion strobing (blurring of the subject when fast movement occurs). Thus so, progressive scanning video cameras tend to be more expensive than their interlaced counterparts. (Note that even though the digital video format only allows for 29.97 interlaced frames per second [or 25 for PAL], 24 frames per second progressive video is possible by displaying identical fields for each frame, and displaying 3 fields of an identical image for certain frames. For a more detailed explanation, see the adamwilt.com link.)
Standard film stocks such as 16 mm and 35 mm record at 24 or 25 frames per second. For video, there are two frame rate standards: NTSC, and PAL, which shoot at 30/1.001 (about 29.97) frames per second and 25 frames per second, respectively.
Digital video can be copied with no degradation in quality. No matter how many generations a digital source is copied, it will be as clear as the original first generation of digital footage.
Digital video can be processed and edited on an NLE, or non-linear editing station, a device built exclusively to edit video and audio. These frequently can import from analog as well as digital sources, but are not intended to do anything other than edit videos. Digital video can also be edited on a personal computer which has the proper hardware and software. Using a NLE station, digital video can be manipulated to follow an order, or sequence, of video clips. Avid's software and hardware is almost synonymous with the professional NLE market, but Apple's Final Cut Pro, Adobe Premiere, and similar programs are also popular.
More and more, videos are edited on readily available, increasingly affordable hardware and software. Even large budget films, such as Cold Mountain, have been edited entirely on Final Cut Pro, Apple's non linear editing software.
Regardless of software, digital video is generally edited on a setup with ample disk space. Digital video applied with standard DV/DVCPRO compression takes up about 250 megabytes per minute or 13 gigabytes per hour.
Digital video has a significantly lower cost than 35 mm film, as the tapes can be viewed on location without processing, and the tape stock itself is very inexpensive (about $3 for a 60 minute MiniDV tape, in bulk, as of December, 2005). By comparison, 35 mm film stock costs about $1000 per minute, including processing.
Digital video is used outside of movie making. Digital television (including higher quality HDTV) started to spread in most developed countries in early 2000s. Digital video is also used in modern mobile phones and video conferencing systems. Digital video is also used for Internet distribution of media, including streaming video and peer-to-peer movie distribution.
Many types of compression exist for serving digital video over the internet, and onto DVD's. While DV video is not compressed beyond its own codec while editing, the file sizes that result are not practical for delivery onto optical discs or over the internet, with codecs such as the Windows Media format, MPEG2, MPEG4, Real Media, the more recent H.264, and the Sorenson media codec. Probably the most widely used formats for delivering video over the internet are MPEG4 and Windows Media, while MPEG2 is used almost exclusively for DVD's, providing an exceptional image in minimal size but resulting in a high level of CPU consumption to decompress.
As of 2005, the highest resolution demonstrated for digital video generation is 33 megapixels (7680 x 4320) at 60 frames per second ("UHDV"), though this has only been demonstrated in special laboratory settings [1]. The highest speed is attained in industrial and scientific high speed cameras that are capable of filming 1024x1024 video at up to 1 million frames per second (for very short time, obviously).
2006 Cordin is the world leader in ultra high speed imaging technology.
Depending on the camera system in use frame rates up to 200 000 000 frames per second are possible. Very short integration times and inter frame times are standard. Gated and intensified models are available. Among other modules Cordin offers Ultra-High Speed Camera systems with 1000 * 1000 Pixel at full frame rate in colour or black and white . Streak camera systems for scientific applications are available and developed with modern technology.
For high speed applications in the near, middle or long wave infrared the Phoenix cameras offer various possibilities. The InGaAs, QWIP and InSb Detectors can acquire images with a frame rate of up to 30 KHz in the wavelength range of 900 nm to 10 µm.
interfaces/cables Many interfaces have been designed specifically to handle the requirements of uncompressed digital video (at roughly 400 Mbits/s):
- Serial Digital Interface
- FireWire
- High-Definition Multimedia Interface
- Digital Visual Interface
- Unified Display Interface
- DisplayPort
Encoding All current formats, which are listed below, are PCM based.
- CCIR 601 used for broadcast stations
- MPEG-4 good for online distribution of large videos
- MPEG-2 used for DVDs and Super-VCDs
- MPEG-1 used for video CDs
- H.261
- H.263
- H.264 also known as MPEG-4 Part 10, or as AVC
- Theora standardized but still in development. used for video over the internet.
- Betacam SX, Betacam IMX, Digital Betacam
- D1, D2, D3, D5, D9 (also known as Digital-S)
- DV, MiniDV - used in most of today's consumer cameras
- DVCAM, DVCPRO - used in professional broadcast operations
- Digital8 -
- Video CD (VCD)
- DVD
- HD-DVD
- Blu-ray Disc
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