Post-production systems of DV format

By Oleg Bondarev

Review contents:

Post-production systems of DV format The mobile DV-solution from Apple AVID systems for TV programs post production in DV format Canopus DV Storm2 Pro System NewsBaseDV System Serial-4-Cam for preparation of material at multicamera shooting DV-installation: variants are possible Videoediting stations of DV format from Matrox Company Systems of Pinnacle Liquid Edition series DV Rack from Serious Magic Program-making system DV Station

Old and delayed “war of formats” in sector of professional video, received the new pulse in connection with impetuous development of digital technologies, is proceeded with variable success. Many digital formats, apparently, providing with many advantages, either have sunk into oblivion, or live last days. Others, on the contrary, are impetuous developed, restricting the digital and analog competitors. On this background the indisputable leader is DV format.

Initially considered almost as household, today DV format has won a strong place in the professional environment. And it is not surprising, our correspondents inform, its many user characteristics in fact are unique enough. First of all, it concerns the quality of record and weight-dimension parameters of the equipment of this format. Packing density of DV-information is very high — more than 0.4 MB/mm², and the dimensions of miniDV cassette, which is intended for 60 minutes of video recording, only are 66×48×12.2 mm, that is approximately as thin matchbox.

It allows developing of camcorders, on its sizes hardly exceeding the medium camera named as “soap tray”. Therefore with occurrence of the first such cameras DV format at once has began popular, especially among TV reporters. Agree what to carry the whole day 5…10 kg of “live weight” for a cameraman pleasure is low. And now we shall take the DV-camera with decent optics and we shall receive only 1.5…3 kg — you must agree that difference is essential. And visually perceived quality is so high, that by the first it had amazed the imagination even of professionals though there it is not so fluent.

First of all, feature of DV format is the method of video information encoding. As is known, the base standard of the signal representation at component digital encoding in TV is the version 4:2:2. In application to digital technologies it means, that for encoding of luminance 8 bits are used and on each of color-difference components 4 bits are used. In DV format the standard of data presentation 4:1:1 (PAL) or 4:2:0 (NTSC) is accepted. Transition from 4:2:2 to structure with the lowered color resolution is carried out due to deletion of each even sample in vertical or horizontal direction accordingly. Resolution of brightness component is suited to studio quality, and resolution of color-difference component is twice lower, that is, roughly speaking, color resolution is four times lower than brightness resolution. Such decision is the compromise which allows to lower the bit stream up to 25 Mbit/sec, with keeping of visually acceptable quality. Additionally to the cut down sample for reduction of DV-stream the intraframe compression of separate pictures by algorithm DCT (discrete — cosine transformation) is also applied. The back side is sensitivity of this format to specific conditions of shooting. The matter is that the algorithm DCT in application to video compression is well worked on bright contrast close ups with slow smooth movement. If a video row is picked up correctly any problems do not happen, and even the expert will notice nothing. However as soon as we will shoot the general scene with weak contrast and illumination, for example in twilight, — we receive characteristic “digital” artifacts in the frame. Behind examples far to go it is not necessary — the first attempts of application of the DVCPRO equipment (by many characteristics this format is similar with DV format) for shooting of sports competitions some disadvantages have evidently confirmed: the greased panorama of tribunes, crushing and sharp loss of quality of display of quickly moving objects, visible fall of quality and definition of color reproduction on scenes in details.

DVCAM (with recording on miniDV cassette) and MPEG IMX camcorders

Owing to the color resolution that in DV format is four times lower than brightness resolution it is difficult to make keying, that is a cutting on a color key. But color “step” in the image contour is twice higher brightness, thus the contour will be notched even if with luminosity will be all right. Why we do not see it in original material? The matter is that the human eye is more sensitive to luminance, than to color, therefore, if keying is not applied, we can see clear contour, to the computer it is “all the same” and it reveals this serrated profile. Thereof the qualitative multilayer editing in DV format is practically impossible — even if as much as possible to increase the handicraft portion, the result turns out poorly suitable for commercial use.

Though presence in DV-tape recorders analog (composite and Y/C) inputs/outputs is easily allowed to integrate them with the available equipment, the main thing in DV, certainly, is a digit. On the basis of computer protocol IEEE 1394 (FireWire) the new digital interface DV known also under the name i.Link was developed. With this interface by digital stream it is possible to transfer video, audio, time code, executive instructions — and all with one cable only. The most interesting feature inherent to DV, as to the majority of digital formats, it is, certainly, the real opportunity of transmission of video/audio information in digits without loss of quality. Twenty five consecutive copying for this format is not any problem (certainly, if i.Link is used) while at “shuttle” with analog interfaces the quality of the third…fifth copy will be visibly falls. Besides it, due to digital technology already during shooting on the cassette it is possible to put marks, that in further will simplify and accelerate the editing, but is the truth, that a cassette should be special — with the built-in chip of memory.

It is necessary to tell, that some lacks of the format are continuations of his advantages. In connection with diminutiveness of the miniDV cassette the high demands to accuracy of its manufacturing are made; in the opposite case the step to the left, the step to the right — and the cassette begins “to be scattered”. I personally have faced with situations when in unsuccessful set of the cassettes which are by form are not differed from normal and were bought in reliable source, practically everyone the second gave out dropouts already during at once. MiniDV cassettes with set of fine details are more fragile and sensitive to dusting too. The same can be told about tape transport mechanism, therefore the reliability of functioning of DV techniques will depend both on quality of manufacturing, and from accuracy in handling and operation.

Despite of fine roughness of DV format, anything the best for the certain circle of tasks till now is not thought up. Not without reason the largest manufacturers not only have accepted it as a base for creation of the digital formats, but also have ensured the compatibility of new formats with “old kind DV”. I have means the Sony DVCAM and Panasonic DVCPRO formats — they are compatible not only with DV, but partly even among themselves, that is absolutely atypical for such implacable friends-competitors.

Well, having recollected fundamental parameters of the DV format, its advantages and disadvantages, at last, we shall pass to the basic topics of this article. As it was already told, in professional operation the DV first of all is used by TV reporters, which should work in heavy conditions: “hot points”, areas of natural cataclysms, man-caused failures etc. DV-format is also convenient for the latent shooting — the camera easily to disguise, it is possible to carry it even in a pocket. However, in our “country of miracles” this initially household format is frequently used even for shootings TV serials. But it is all concerns to shooting cycle, and for us it is interesting to find out, what decisions for operative DV-editing are existed.

As it was already mentioned, since tape recorders of DVCAM and DVCPRO formats may read DV-cassettes the systems operating with these formats, can be also attributed as DV-decisions, therefore they too are included in the review in part.

Methods and means of DV-editing are rather various and their classification is rather difficult, but if to go from simple to complex the DV-decisions, in my opinion, can be divided on the following categories:

• Editing DV pairs;
• Linear DV editing room;
• DV disk-recorders, including hybrid one;
• Nonlinear DV editing room.

Editing DV pairs

Structure diagram of simple editing pair

Essentially the editing DV pair is not differ from pair of any other format. The classical pair includes two VTRs, one of each is operated in playback mode (player), and another — in record mode (recorder), and the output of player is connected to an input of recorder. Normally they are operate under control of the controller — either external, or built-in in recorder. Marking input points (entrance) and/or output points the cutter on a player chooses the necessary fragment (clip), further will put an input and/or output point on recorder and will record a clip in the necessary place of the master-cassette. Thus, there is an elementary editing by direct splice. DV-pair differs from normal that due to its small cassettes it is possible to make it more portable. Also there are the ready editing pairs made as a standalone device. Some manufacturers produce the DV-compatible tape recorders in modular construction so, that they can be joined among themselves, receiving an uniform block-pair. As a rule, they are also added with the small built-in or folding LCD video monitors and may operate from batteries and it allows to edit right after shootings in field conditions.

Structure diagram of linear DV editing facility

Mobile system based on compact DVCPRO camcorder, disk recorder and notebook with editing application

Linear DV editing rooms

This decision differs from previous in that it is two players which are connected to recorder not directly, but through video-mixer and are controlled by external controller. The line may be also supplemented with a character generator, logo generator etc. It is necessary to say, that linear DV edition rooms are used seldom so it is connected both with the general expensiveness of this decision, and with impetuous development of nonlinear technology.

DV disk-recorders

Actually, the disk recorders for video editing are generally auxiliary devices in some cases allowing to replace tape devices, if it is especially necessary to record the large material for which any cassette will not suffice. In this case as alternative to the cassette the hard disk or the whole disk array is come out. If removable disk is in presence it can be further placed in compatible nonlinear editing station and to edit a video material. Some recorders may also operate in structure of a linear equipment room as one of tape recorders, but the application of such kind is limited. Some models of disk tape recorders are provided with the built-in opportunities of editing, the truth, basically at the level of playlist composing. More advanced and more expensive decisions are the combined (hybrid) recorders which can make the recording simultaneously on hard disk and cassette. Themselves such devices are hybrid editing pair as allow to record from an internal disk on the cassette and the contrary. Last word of engineering are the recorders, which are capable to operate with another carriers than hard disk. It may be DVD-R, DVD-RW, DVD-RAM disks, magneto-optic storage and even memory card.

Nonlinear DV editing rooms

Today, it is, certainly, the most numerous class of video editing solutions — they are operated everywhere, from super expensive broadcast channels up to the modest domestic studios.

Basically any nonlinear editing station having FireWire interface may be referred to DV-class. But in this case the spectrum of considered decisions will be so wide, that it is not possible to cover anything in one review. Therefore we shall consider only those decisions which were DV-focused initially, that they are operated with DV format not only from “outside”, but also inside and normally other formats of compression are not supported.

If to speak about a computer platform, it is better to begin with Macintosh. The matter is that in two-three last generations of MAC the interface IEEE 1394 (FireWire) is not simply integrated, but its support is introduced at the level of the operational system nucleus. Therefore, if to add to MAC any appropriate software (for example, Final Cut Pro), — we shall get the ready nonlinear station of DV format. It is necessary to add a disk array of the needed volume which, by the way, can be also connected on FireWire, and we can to edit. Besides an input/output, such editing room can reproduce some DV-streams and also generate effects in real time; however, it is far from being all. And the number of streams and effects will depend on capacity of the computer, number of processors etc. Such station is provided with single disadvantage: impossibility of an input/output of video under analog interfaces. Even if the editor is provided with digital equipment only, nevertheless, it is very useful to carry out a preview on the analog monitor; that is will allow to avoid errors of color reproduction. The simple and inexpensive decision of this problem is the application of external analogue-DV and DV-analogue converters. There are the bidirectional versions — they are most universal, and the advanced models can be provided with component interfaces and symmetric audio path. Such converters are produced by Canopus, Datavideo, COMO and some other companies. If it is necessary any portable NLE on MAC, it is simply necessary to use computer — notebook Powerbook, in the rest the requirements are the same: software and external disk FireWire or USB are necessary.

With platform PC it is a little bit more difficult — the presence of IEEE 1394 in the computer is not guaranteed. If it is not present, it is necessary to buy an additional board of the FireWire-controller ($15…40) plus to install the editing software. The truth, opportunities of real time on PC in absence of special accelerators are limited and in large degree are defined by “correctness” of software package. But here is much wider, than for MAC, a choice of boards and hardware-software complete sets which can make effects as basing on its own computing capacities, and on high-speed characteristics of the computer. Practically all these boards initially have an opportunity of an input/output not only on DV, but also on analog interfaces, that essentially expand their opportunities and remove any necessity in converters. Besides many effects, especially three-dimensional effects, in real time by means of MAC platform it is impossible to make while the PC boards make them as hardware. Well, the last — the background calculation on MAC is not realized till now, and some editing software packets on PC this are perfectly supported, and it allows to save editing time essentially. As to portable decisions there is all the same — simply we shall take notebook with built-in or additionally installed interface IEEE 1394, then we shall add editing software of wide choice and the editing can begin.

Now, when the general provisional classification is clear, it is possible to consider any concrete decisions of DV-editing.