Slowly and smoothly…

By Michael Zhitomirsky

Review contents:

Slowly and smoothly… Abekas 6000 MultiFlex server from Accom BLT Video Server: Tools for Sports Controllers from DNF Controls Systems of the slow motion on the basis of disk recorders by Doremi Labs EVS systems of slow motion and reply Geevs V4 Sports II Controllers from Hi Tech Systems Multichannel system of replies TimeNRunner of company JC System Integration Whiplash2 video repliy system from Leitch

Frames of slow motion have appeared on TV screens relative recently, however they became so habitual, that sport translations, programs about a nature, feature films and screen products of other genres without them are impossible. It is difficult to imagine, that yet so for a long time it was exotic.

It is no doubt that slow motion allows essentially raising emotional impact on the spectator. And not only emotional. The slowed reply gives the audience much additional information latent during playback with rated speed owing to high speed of passage of this or that process. For example, attacking throw of the snake is so impetuous, that the human eye practically does not fix it. In the slowed reply of the goal moment or bright dribbling of the football player there is a low informative filling, but it allows to feel the heat of game and to see the maximal stress of the player and his master skill of dodging. And such examples it is possible to represent many more.

At first sight in slow motion of cinema or a video material there is nothing special — it is necessary simply to take and to decrease the speed of drive of a film in a projector or to slow down the movement of a magnetic tape in the VTR. However it is only apparent simplicity. One of serious problems is… human vision. It is arranged so, that perceives changeable static images (frames are static pictures) as the continuous image only in the case that frequency of their change does not fall below 24 per second. If it will be lower than this value the image is perceived discontinuously. Therefore if by simple reduction of the frame rate under shooting with normal speed it is possible to achieve some effect of delay, but only insignificant. For an example it is possible to say, that in PAL standard where the frame rate is equal to 25 Hz, this delay is only 4% as it is possible to reduce this frequency at playback only by 1 frame/sec. In NTSC standard (30 frame/sec) this percentage is a little bit above and comprise about 20% (6 frame/sec), but all the same a problem does not solve, the first, because it is insignificant, and the second, because does not allow to carry out the various tricks decorating translation, in particular smooth transition from a freeze with acceleration to a mode of normal playback.

Quite natural conclusion follows from these discussion, that it is necessary simply to shoot with higher speed, than with nominal speed and then to reproduce a material with a normal frame rate. It was made all over again on a film, and then and in sphere of video. However here all not so is simple. The first with what it is necessary to face, is necessity of increase sensitivity of the film or sensors of the electronic camera. Therefore the effect of the slow motion even at cinema has appeared far from being at once. Let’s recall, for example, that at the beginning of photography from which the cinema has then grown also, for receiving of clear portrait picture the poor fellow must be set during some tens minutes in the broiling sun and do not move. Otherwise the picture turned out blurred. The reason was low sensitivity of a material for shooting. Certainly, in due course the film sensitivity was increased and, eventually, began to allow carrying out shooting with the high frame rate. Then the effect of slow motion at cinema has become a reality. But this trick was expensive enough as the cost of high-sensitivity film was high and this film was applied only to shooting those fragments which it was planned then to slow down. There are two reasons: the high price of this film and an inefficiency of its use in a normal mode because of the same high sensitivity.

However in TV it hardly would find any application because of prolonged chemical processing. It is necessary to show an interesting material immediately after it was shot. In the extreme case it is necessary to edit the cutting of such moments and to show it in a break of a game or during a pause of sport competition.

Firstly in TV the reply was out of the question because of the video recording simply did not exist. All programs went to the air and represented not alternatively, as live translations of those or other events: concerts, sports competitions, speeches of politicians etc. The only things that were made as “records” for the air transmission were the movies which were broadcasted from telecines. Revolution has taken place in 1956 when the first VTR has appeared. It has allowed carrying out broadcasting with a delay concerning time of event, and after minimal time began to possess by editing functions. The opportunity of replies had appeared, may be not at once after the interesting moment, and after any times rather essential, as editing was still imperfect and prolonged. It is possible to argue on advantages and disadvantages of tape technologies for a very long time: they are well-known. But one of these disadvantages it is hardly to overcome with reference to slow motion. The question is the linearity of VTRs.

Until in TV production and broadcasting tape technologies were reined, the way out was only one: to shoot with high speed, and then to playback with normal or lowed speed, but not falling below limit value of a frame rate. And to ensure if not fast then not too delayed reply, some devices were necessary to put on recording, and at occurrence of the situation requiring for reply, one of them to stop, rewind a tape and repeat the fragment. It was unreal to execute such reply two times in succession. Possibly this it is not too perfect method. And high-speed cameras are high-cost as they require the high-sensitivity matrixes capable at in some times reduced luminous flux, falling onto each frame, to ensure the picture quality not worse, than normal cameras in a normal mode. And in any case assembly of a scene, first, demanded, as a minimum, two devices — for playback and for editing, and second, for this purpose it would be needed the recorder stop required even to withdraw the cartridge and to place new one to recording. Also, the recording time was limited by the cartridge longevity.

Certainly, the prospect “to win” all these problems was tempting, and the computer technologies became optimum decision. The opportunity to expand the storage volume, random access to material, and without necessity to wait the digitization completion, practically instant transition to the necessary fragment — all this made the computer by very favorable decision of all problems. However computers too needed “to grow up”, you see firstly the systems working from video, were very slow, unreliable, transmission rate of the buses and disks left to wish much the better, and the input/output boards were hardly coped with low resolution video. But light at the end of a tunnel was already seen.

Ampex HS-100 disk recording device, 1967

And, at last, in 1995 the new company EVS Broadcast Equipment which was organized only one year prior to that has presented to the TV community the first-ever system capable not only simultaneously to carry out record and playback of video, but also to carry out slow motion in real time. The name of this system is LSM (Live Slow Motion). Immediately the system was bought by sports editions of channels BBC in the Great Britain and Canal+ in France. Year after, during realization of Olympic Games in Atlanta (USA), in translations it was involved already 45 these systems, and companies EVS and Panasonic, having united, have developed the technology Super Motion at which shooting was conducted with the speed three times exceeding nominal. Well and is farther, as they say, the process has gone. Presently the video servers with realization of function of slow motion are produced not only by EVS Company. These systems are produced by Accom, Doremi Labs, Gee Broadcast Systems, Leitch (after buying of dps Company) and some others. Do not lag and leading Russian manufacturers of the equipment. For example, the JC System Integration Company is quickly coped with the technology and, having begun with two-channel system, already today is offered the multichannel video servers with slow motion playback and reply.

EVS server (above) and one of the first disk recorders from Accom

The reason of such quick growth of video servers is the impetuous progress of computer technologies. Now the computers may process not only standard video, but also high resolution video, and both with and without compression. Power and productivity of the input/output boards has considerably increased, the hard disks have fallen in price and at the same time there begun more perfect. And still the principle of realization of slow motion has not changed. This principle is still: “Concerning normal playback it is necessary to increase the number of frames for qualitative slow motion”. The principle, certainly, has not changed, but one more method has appeared to achieve the desirable result: the artificial creation of additional frames on the basis of the frames shot with normal speed. By other words it is the interpolation. Now there are systems with the same 25 frame/sec “to multiply” them, having increased this number twice, and even three times. It is necessary to note, that it is not simple copying of the next frame. Interpolation assumes a complex mathematical process on the basis of which the analysis of movement in the next frames is made, and on the basis of this analysis one or several intermediate frames are created. They are created so that the movement in really next frames shall not be interrupted or deformed. Only in this case it is possible to receive the high-quality slow motion.

Certainly, video servers with interpolation are more expensive than usual video servers, realizing slow motion in pair with high-speed cameras. However in this case the economy can be achieved (and it is reached) by opportunity to apply the normal video equipment — cameras, VTRs etc., receiving the qualitative slow motion. If in the equipment park of a broadcasting organization there are high-speed cameras already, that, certainly, there is no sense to buy the expensive Slow Motion system, and it is enough to buy the equipment capable together with such camera any necessary task to solve. Also it is necessary to mean, that functions Slow Motion and Super Slow Motion differ from each other because the latter assumes the triple delay concerning rated speed of playback. Also there is a probability, that the system with the interpolation, capable to carry out the Slow Motion function on the basis of normal video, will be appeared as powerless as compared to Super Slow Motion for which it is also necessary the high-speed camera.

Therefore, before to choose a system of slow motion it is necessary to consider carefully all and attentively to study the description of the system assumed to purchase. If it is underlined, that the high-speed camera is necessary so such system is practically guaranteed that it does not provide the interpolation of frames and without such cameras may work only as a multichannel video server.

In the rest all systems of slow motion and reply are very similar. They have one or several channels for recording and, as a minimum, one cannel is on playback. All of them allow starting the work with video after some seconds after the beginning of digitization. There are also the editing functions submitted to some degree, beginning from simple direct splice of the chosen fragments and finishing by three-dimensional transitions and effects for what the system may contain the hardware module of special effects. Practically each system works with off-the-air schedules and may operate by other equipment on any of interfaces.

Though computer technologies are occupied the more wide niche in TV production and broadcasting, the video recorder past has still persistently an effect. And this is not only a simple habit. You see the tape technology was perfected at all by not years only, but during some decades and consequently on its ground the very many interesting and useful achievements are arisen. In particular, there is the user interface allowing easily, quickly and evidently to operate by all modes of recording, playback and editing. For this reason the controllers, which are characteristic for linear editing systems, have removed to the nonlinear environment as well. And these controllers retained some characteristic controls, as keys for recording, start/stop, rewind, and also habitual handles Jog/Shuttle and T-Bar. The last easily and simply allow to operate by direction and playback speed of a fragment (nearly I has not told “movement of a tape”).

Certainly, in one article it is impossible to tell about everything, concerning to slow motion. The materials following further about the concrete equipment will allow to create more detailed and objective picture in this sphere.