Digital Video (DV) is the generic term for the DV standard, which was introduced in 1994. It includes the cartridge formats DV, MiniDV, DVCAM, Digital8, HDV, DVCPro, DVCProHD and DVCPro50.
- 6.1 Memory requirements per cartridge
- 6.2 Automatic scene detection
- 6.3 System-based limits of the possible file size
Development and dissemination
After the start of 1996, the Digital video made a rapid development. As early as 1999 there were products from a variety of manufacturers, the prices fell steadily. Originally intended for the consumer market system set out for the outstanding quality fast and professional purposes a good name.
The images are digitally recorded and reduced to about 10 percent of the original analog memory requirements. The individual images are encoded in the DV standard individually independently using a JPEG -like process. It is initially just like an analog signal, a Chromadownsampling ( halving the color information, since the human eye for color vision has a lower sensitivity than for brightness differences ) in the ratio 4:1:1 (NTSC) or 4:2:0 (PAL ) causing a data reduction by half, followed by an exclusively digital image compression based on discrete cosine transform ( DCT). The method is thus similar to MJPEG and, in contrast to MPEG the advantage of being able to cut videos at any point without loss of quality.
The data rate DV stream is at 3.125 MB / s (25 megabits per second), or about 1 gigabyte per 5 minutes. The quality is better by far compared to older analog SVHS cameras and provides magnetic recording at a low price. This led to a growing acceptance in the broadcast sector.
DV used as screen resolution 720 × 576 pixels ( PAL) or 720 × 480 pixels ( NTSC). In the PAL format 50 fields per second ( 50i ) are recorded. Some DV cameras also allow full image recording with frame rates 24p and 25p (also known as progressive scan ).
As an audio format a sampling rate of 48 kHz and a resolution of 16 bits (like the DVD -Video standard ) used in DV. Audio dubbing another audio format with 32 kHz and 12 bit is defined in the standard, in which case even four tracks can be recorded. Some editing programs can not edit this rarely seen sound format. Furthermore allowed the DV format, 44.1 kHz sampling rate than to use (like the audio CD standard ). However, there are only a few devices that make this possible. When DV format picture and sound are out of sync; MiniDV format, a sound-image offset of ± 1/3 frame ( 13.33 ms) is allowed.
For amateur and semi-professional applications, the MiniDV has prevailed, which has almost the same data format as DV. MiniDV cassettes ( 120 minutes long play 80 minutes standard play / ) offered in capacities of 60/90 (60 minutes standard play / 90 Minutes Long Play) and 80/120, whereby the use of the latter due to the thinner and thus more sensitive tape in general is not recommended. The cassettes are ( netted on the season ) is far cheaper than the approximately twice as large, standard DV cassettes, which are used only in the semi-professional and professional field.
Compatibility with DVCAM
A MiniDV cassette can be recorded with appropriate equipment in the professional DVCAM format. Since these devices transport the tape recorded but faster, as indicated on the cassette recording time is reduced here. However, DV tapes are not designed for up to four times higher belt speeds.
Most DV camcorder in the consumer sector, but also some semi-professional devices have a long play mode in which increases the time per cartridge by 50%. In a DV cassette with regular 60 minutes gameplay fit as 90 minutes. The special thing about it is that the use of Long Play DV mode, in contrast to most other video systems leads to no loss in picture and sound quality. This fact led many users to frequent, if not continuous use of long play, as this can be saved without the user directly apparent disadvantage band and therefore money. In fact, however long play involves a number of drawbacks and dangers.
The DV- Long Play mode does not correspond to laid down standard. It is therefore up virtually every manufacturer from DV devices to make the LP mode in its sole discretion. In practice, however, the manufacturers have agreed to certain tolerances in order to at least begin to achieve compatibility. Nevertheless, the exchange of DV tapes that were recorded in long play mode, extremely problematic. Often an error-free playback is only possible on the device on which the tape was recorded. Even on other models of the same manufacturer, it may be encountered during playback.
For DV the same data on the tape are stored in long play mode exactly as in the SP mode (hence the identical quality). However, the belt runs at a reduced speed by 33 %, this results in a lower track width. Due to the greatly increased data density but little flexibility to compensate for any error band, which leads to frequent dropouts. Similarly, the signal strength is on the tape in the SP mode and considerably less sways with a newly recorded tape just above the readability limit. All of this means that discs recorded in LP mode DV tapes generally have a very short life and often are no longer readable after a few years.
In most cases, only the cartridge formats DV and MiniDV, which are recorded with the conventional DV codec, with the term DV in the narrower sense. In addition, already exists the HDV codec, which allows recording of HD data on these two cassettes formats.
A similar technique using the professional formats DVCAM ( Sony ), and DVCPRO (Panasonic), in which case the tape is transported faster, which is to be expected with less data loss. DVCPro50 even at the double data rate (50 Mbit / s) work order to achieve a higher quality. Furthermore, there is also Panasonic DVCProHD format that is used, for example, in the camera system varicam. This format has a higher resolution than the standard DV format and is used for recordings in HD resolution. In the future, high definition video in the AVCHD format to be recorded, which is also supported by Panasonic, Sony, Samsung and Canon.
Digital8 is a further development of the digital line Video8/Hi8 used the cassette format that is the same as the analog predecessors but uses conventional DV codec.
The computing devices have among other things the same analog interfaces (composite, S-Video) video devices such as VHS or Hi8 format. Therefore, one does not need a PC to play back the data to the TV. To be able to copy and thus lossless digital, the developed parallel to DV FireWire interface will be used. This compound, often referred to as a DV -out is employed for the data transfer to and from the PC. Since the data packets are transmitted without loss or conversion, the load of the processor is very low.
Some camcorders have next to a DV output via an input, called DV -in. In addition to 1:1 copies from one to the other camcorder is equipped with such devices also possible on the PC edited videos lossless play back on MiniDV. Technically, any DV camcorder would have a DV -in (which eg in the USA or in Japan do), but since camcorders are fiscally considered with DV Input port in Europe as a video recorder, resulting in higher import duties are incurred, was the DV -in on many models from manufacturers intentionally disabled. Often there are also two versions of the same model, which differ only by DV - In and the consequent higher price. Some camcorders have in addition to the DV -in via an analog input, through the example VHS tapes can be recorded on MiniDV.
In older MiniDV camcorders DV -in was purely locked at the software level, and could therefore often be activated with little effort again. Instructions, can be found as well as cable and software required even today on many websites. Legally, the " unlock " the DV -in was not banned, but often they lost at such modified equipment warranty. The manufacturers responded to this by and by with a hardware-based deactivation of the DV input, so that the subsequent unlocking of the DV -in with current models is no longer possible. Professional camcorders and DV / DVCAM VCRs usually standard with a DV input.
When transferring the video stream from the camcorder to the PC, the DV material is usually stored in the AVI container format on the hard disk. The video file then has the file extension ". Avi". Apple's Macs use mostly " QuickTime Movie " as a container format and the file extension ". Mov ". DV is the standard format for video editing in Apple (such as iMovie, Final Cut Pro).
Memory requirement per cartridge
Although most DV camcorders have a (mostly hardware-based ) compression codec, nor result fairly high bit rates and associated large amounts of data. The DV codec, which is identical for MiniDV and DV ( in contrast to the cassettes) with stereo sound provides a data rate of about 28,000 kbit / sec. This corresponds to about 0.2 GB per minute DV with stereo sound. It follows:
- 60 minutes DV: 13 Gigabyte
- 80 minutes DV: 17 Gigabyte
Automatic scene detection
However, this need not necessarily be identical with the size of the thus obtained individual files; so you can, for example, in many capture programs an automatic scene recognition based on the recorded data codes - which also contains the date and exact second time of recording in addition to information about various camera settings - make, provided you have set the time the camera before shooting, so that at each interruption of this data codes of at least one second a new file is started. Some editing programs also support an automatic, chronological sorting of the recordings, even if they are located on different bands or were even taken with different cameras. In some devices in the consumer sector date and time are only kept in volatile memory, so they have to be reset upon removal or complete discharge of the battery.
Not to be confused is the data code using the timecode, which is also recorded from all DV devices.
System-based limits of the possible file size
Usually, however, a DV cassette 1:1 occur when transferring the contents to a PC very large files. One must therefore make sure that the file system of the hard disk supports this,
- Such as the Windows NTFS used by having an upper limit of 16 per file TiB.
- Contrast, FAT16 has a max. File size of only 2 gigabytes (ie only about 10 minutes of DV data), FAT32 4 gigabytes.
- The default HFS file system on Apple computers also support large files up to 16 terabytes
- Linux and Unix file systems are also known to any significant restrictions (eg ext3: 2 terabytes, ReiserFS: 1 Exabyte, XFS: 8 exabytes, btrfs: 16 exabytes ).
In addition, was formerly the file format used by importance. The size of an AVI file was in fact limited to 4 GiB due to the internal structure. This limitation is now omitted. With MOV files were and are in this respect no significant restriction.
To work around this problem, virtually all support Capturingprogramme an automatic file splitting, so that automatically creates a new file is started after reaching the permissible from the respective file system maximum size. Some manufacturers, such as Canopus also support so-called reference -AVI.. Doing a virtual avi file is created which contains only the information about where on the hard disk is the actual video data - split into small, individual files (often with extensions like .001, .002, etc.) - are located. Editing programs handle these reference -AVI then like a large, unlimited in length video file.
DVD Authoring: From the DV file to DVD
The data can be easily processed with different video editing programs, nowadays, you can easily achieve very effective effects such as transitions, titles etc. with most standard PCs.
To get ultimately the produced video, for example, into a DVD -compatible format, it needs further compression as a standard DVD comprises only 4.7 GB. The default codec for DVDs is therefore the more compressed MPEG-2 format to which the DV data to be converted. For the conversion on the PC, you need a DVD authoring software, which ensures that in describing the DVD to popular video and DVD standards are met so that they can be played in any standard DVD player. Some video editing programs are already equipped with such a feature.
DV camera vs. DVD camera
Unlike camcorders with built-in DVD burner DV cameras still have a significant quality advantage, since the raw material is only slightly compressed stored on the tape, which is particularly in post-production (editing, etc. ) effect. In a " DVD Video Camera" on the other hand, an integrated real-time MPEG2 codec for compression provides; this may have greater losses depending on camera type and quality setting, with MPEG- 2 remains generally involve greater losses in quality than DV.
Another advantage of the MiniDV devices is that the images on the MiniDV tape - according to current knowledge - remain considerably longer preserved in their original quality on DVDs; On the other hand, there are already camcorders that record to DVD-RAM.