What our experts say…
There is little doubt that the future of video recording lies with digital disc-based technology – in the medium term at least – but it is clear that video tape recorders are not going to disappear overnight nor, it seems, are they going to give up without a struggle.
VHS video cassette recorders have been a cornerstone of video surveillance for at least the past 20 years; blank tapes and hardware are relatively inexpensive, the equipment is durable, reliable and recordings are easy to archive. Sadly whiskery old VHS or even Super VHS cannot compete with most recent digital systems when it comes to picture quality, nor can it match the speed and ease of access to recordings of some (but by no means all) disc recorders but there is still some life left in the old dog yet!
The Panasonic AG-DTL1 time lapse VCR is an interesting combination of technologies, recording high quality digital video on standard S-VHS tapes. The DVC PRO recording system appears to be something of a hybrid with what looks like elements from analogue VHS, Data-VHS and domestic camcorders, enabling recording times from three hours (real-time) to 960 hours time lapse from up to 16 camera inputs.
As we shall see, it is an impressive achievement. However it is worth bearing in mind that unlike analogue VHS time lapse recordings, which are very widely used and compatible across a broad range of products and brands and tapes can even be played back on domestic VCRs (at a pinch), this is – so far – a single-brand proprietary format and therefore more than usually dependent on the manufacturer keeping faith with it for a good few years to come.
Incidentally, it is a shame that Panasonic did not take the opportunity to make the machine backwards compatible with standard VHS. (We suspect it would have added comparatively little to the cost). Such a facility could prove useful to end-users during a changeover period and in the future for reviewing archive material.
But we digress, time for some facts and figures. The machine has two recording quality settings and frame or field recording modes. There are 13 time lapse speeds in addition to three-hour real time (9, 12, 18, 24, 48, 72, 96, 120, 180, 240, 360, 480 and 960 hour), and playback can be either full screen single camera, sequenced, or four camera quad (unfortunately the quad mode is only available during playback). Other playback options include reverse play, still and fast picture search.
Playback speed can be altered by changing the time-lapse mode, which is just as well as the picture search facility is a bit feeble and cannot be locked, so you have to keep the button pressed, which is not very convenient if you need to skim through a long recording. The machine has an extensive range of alarm and timer functions, including record start from stop or timer mode. It has an alarm and power loss log (up to 99 events) and alarm search. The timer can be set to switch the machine on and start recording at weekly or daily or one-off intervals, or it can be controlled using an external timer.
Resolution is quoted at 520 lines (320 lines standard mode), which is more than twice that of standard VHS and a 25 per cent increase over S-VHS. Moreover, being digital, noise levels are very low indeed.
Surprisingly, given the capabilities of digital recording systems, audio is recorded on what looks like a standard VHS linear edge track, which means the quality is pretty dire in the three-hour real-time mode, and rapidly descends thereafter in the four time-lapse modes with an audio recording facility (9, 12, 18 & 24 hours).
The machine has an RS232 serial communications port, which can be used to connect it to a PC. This enables full access to the VCR’s transport controls and menu system; additionally the PC can monitor the machine’s status and carry out a more precise search by specifying single frames of a recording.
The AG-DTL1 is approximately the same size and shape as a conventional VHS time lapse VCR. In fact the only unusual feature is the position of the deck mechanism, which is on the left side of the machine rather than the more usual central layout. The tape hatch cover is also transparent, so you can see if a cassette is loaded.
On the front panel there are three buttons for tape eject, record and record review, the latter displays a couple of frames recorded before the button was pressed (for no good reason or apparent benefit that we could see). Behind a hinged drop down flap is a bank of secondary controls concerned with tape transport, menu navigation, mode setting, camera selection etc. The layout is a bit haphazard and it takes some getting used to, but more on that in a moment.
Around the back there are four groups of BNC sockets for the camera inputs, separate BNC and mini DIN sockets for composite and S-Video outputs, two phono sockets for audio in and out, a pair of mini-jacks for a microphone input and wired remote control, a five-pin D-Sub connector for RS-232 serial comms with a PC and a set of screw terminals for external alarm and trigger connections.
Set-up & operation
All set-up operations, secondary controls and the timers are controlled from a set of menu-driven on-screen displays. These are fiendishly complicated to navigate due to the way the controls have been set out.
For example, to get the machine into menu/setup mode it is necessary to move a slide switch, from then on pages are selected using the Play and Reverse buttons, selections are made with the Stop Pause and Rewind buttons, and changes made with the Time Mode buttons.
It is all very confusing and the display itself is not that legible when superimposed on a moving image. However, to make matters even worse things such as the camera setup and timer mode displays are almost totally incomprehensible, and that is further complicated by one of the most impenetrable instruction manuals we have had the misfortune to see in a very long while.
It is littered with some real gems. Figure this one: “When recording always in the same recording time mode instead of setting the mode using the TIME MODE button, set RT1 through RT7 for the REC TYPE item on the setting menu on the P3 RECORDING T-MODE”, and so on. There are pages and pages of stuff like that. It desperately needs re-writing, preferably in English, and while they are at it, someone should have a look at the menu displays, which are way too complicated.
Performance
The manual never really explains the whys and wherefores of the quality and frame/field mode settings, which – contrary to what you would expect – has no bearing on recording times; all time lapse modes are available no matter what setting (high or normal) is used.
However, it does have an impact on the number of fields recorded per second and camera switching times, which can become quite significant depending on the number of connected cameras.
On our test set-up there was a very noticeable drop in resolution, from just over 500 lines in high quality mode to around the 320 lines quoted for normal quality mode. The image in high quality mode is outstanding, very clean with negligible noise levels.
Colours are sharp and natural looking and the contrast balance is spot on. Picture quality dips in picture search mode and it is prone to pixellation or blocking when there is any movement in the scene. Picture search is only about 3x normal speed, which is not much use at all and it is a chore having to hold the button down.
The quad display during replay is very useful but spoilt by the awkward set-up. During recording the choice is between a static single image or a very jumpy sequence, which can be very distracting and is not the sort of thing you expect to see on such a high-end product. There is not much to say about sound quality, except that it is just about adequate in the three-hour real-time mode.
What the manufacturer says …
Our new digital time lapse VCR offers the ideal combination of performance, features and economy for professionals making the transition from analogue to digital recording. Because video surveillance requires extremely long recording time capability, the cost of tape is critical. To keep running costs down, but without compromising on superior picture quality, Panasonic has designed the AG-DTL1, which uses inexpensive S-VHS tape to record high quality digital video using the professional digital DVCPRO format.
Panasonic’s DVCPRO equipment has already won the praise of broadcast and video professionals worldwide. The AG-DTL1 uses DVCPRO’s digital component compression system to deliver clear, sharp pictures with 500 lines of horizontal resolution (in High-Quality mode), which means pictures are free from colour irregularities, ringing, vertical dancing and skew. The use of inexpensive long-recording S-VHS tapes ensures that the running costs of the AG-DTL1 are low.
S-VHS tape is a familiar format to most people, it is widely available, easy to handle and provides outstanding durability for long-term storage.
A built-in frame switcher lets the AG-DTL1 record images from up to 16 cameras. In playback a particular camera can be selected for viewing or high-speed searches. Connecting the AG-DTL1 to an existing multiplexer also allows surveillance recording with multi-window display. In addition, it features dual recording modes, with both modes offering a choice of field or frame recording.
