Seekingadvice

I would really appreciate some technical information from the very knowledgeable people on this forum. The issue concerns a brief clip of CCTV footage that was given to the police along with a complaint that it showed a person vandalising a car parked in the street. The individual output the 15 second CCTV clip from an unknown system onto a USB drive. From a witness statement given by the investigating officer the file was playable on the police computers so presumably was not in a proprietary format. (I'd guess it was .mpeg or .avi) The police technical department burnt the file to DVD. That DVD is the only version of the CCTV clip that I have been able to get following a court order for disclosure. The person who told the police that he had set up the CCTV camera and recorded it, now says that the clip was posted to him anonymously or given him by a person he won't name. There is no possibility of getting any co-operation or honest answer from this person. He will tell any lie no matter how improbable or self contradictory. So this is a kind of detective puzzle. The CCTV footage was in a multiplex 4 channel format. Channel 1 shows an image. The other 3 channels are empty. There is a just discernible signal noise but no image. My first question is how easy or common is it to output CCTV footage as a 4 channel view from a probably cheap consumer system. The models I have looked at seem to offer backup to USB of individual camera files based on archived files by date and camera. Before my second question I need to explain a little more. The copy of the footage burnt to DVD by the police is a PAL DVD because PAL is the TV standard here in the UK. The image file was thus encoded in the DVD as an mpeg-2 file @ 25fps. I extracted the file and exported it as a 25fps image sequence. The quad view incorporates a date and time stamp in the frame at lower right. The clock advances by one second every 25 frames. So it is reliably recorded at 25fps. But the inset image at channel 1 is a time-lapse image. The image advances to the next progressive frame erratically. The frame length at 25fps of each time-lapse image varies between 6 and 10 frames in length. There is no pattern to the erratic frame lengths, and the image does not respect the time code at all. That is the clock advances to the following second while the time lapse image has not yet changed. So you have two adjacent frames @ 25fps where the image is the same but the time code is different. So my second question is if the file was downloaded (backed up) to the USB stick from a secondary device. Would that account for this. i.e. If the player software existed on one device that was viewing the CCTV image on a remote DVR hard drive connecting through the web or wireless, might that account for the corruption of the image file. Or can anyone suggest what else might be going on here. With thanks in advance for any light that can be shed on this conundrum. I've attached a frame from this CCTV clip.

Here in UK there is a Home Office guidance to the police on retrieval of CCTV evidence from private systems. The protocol has been adopted by all the police forces, though that doesn't mean that plod on the ground will be clued up. The advice is that a technical officer must visit the system. establish all the specifications of the system and that it is working. Establish and evidence the present system time displayed. Establish true time from a dependable source such as the speaking clock (a telephone service). The officer should then record any deviation and be able to give evidence of the time record. He should then extract the file in native format and secure any software needed for playback. If in doubt he should seize the hard drive or the equipment taking care not to lose any digital data by so doing. Generally speaking where a defended prosecution ensues the two sides will attempt to agree any areas of evidence possible. Thus if both sides agree the evidence on such details as times of recording beforehand it won't be tested. Only if one side doesn't agree would the officer need to give evidence of his notes and procedure on retrieval, which would then tend to support one view unless the other side could throw doubt on it. I think I am right in saying that O J Simpsons defence was largely based on throwing doubt on circumstantial evidence of timings by reference to media camera coverage of events, and tracking the timings on news ENG cameras which were then customarily set by the cameraman's wristwatch on the day of the assignment.

Thank you very much . That is very helpful. It would be very significant if the original had been tape based because not only would the person who recorded the CCTV have possessed an original other of the image, he must have known he possessed it. One cannot be oblivious of having to put new tapes into a machine. If the original had been recorded to tape, would the image size have been likely D1 equivalent (768x576) ? I suppose it's difficult to equate analogue to digital easily, and I'd guess it would be expressed as lines (625?). But in rough terms equivalent?

Thank you so much for all your replies, particularly to Groucho Boucho. It really is helpful because until a while ago I knew a fair bit about imaging generally and a little about cinematography, but was entirely ignorant about CCTV systems and technology. The technology is advancing at an astonishing pace. My problem is now historic because it relates to the beginning of 2009. So the equipment used must have been acquired before that date. So it could be of any vintage but not newer than December 2008. I do have an interest in the matter, but that is beside the point. I'm interested in establishing facts that can be stood up, whether for or against any suspicion. So any pointers are really helpful. I'd like to show a couple of other images, for your thoughts . The first shows the first six frames @ 25fps of the recording. I've brightened the shadow tones to make it clearer and added the red circles. When the file opens only Channel 4 shows in the quad view. By frame 3, Channel 4 comes on line. By frame 5, Channel 1 comes on line and Channel 2 follows at frame 6. Is this consistent with demuxing of a multiplex file occurring from a standing start. i.e. where the transfer is being initiated from a bookmarked place in the file? If so does this shed any light on the device outputting the movie file? The second image shows the channel 1 image where one of the time-lapse images has a horizontal bar. I don't really know what to think about this. It's obviously a phase issue or an analogue glitch caught in the digital file. It occurs to me that it could be of no particular significance. But it may reveal something to CCTV insiders. Is this a common issue in CCTV? Any thoughts? Thanks again for your help.

If I've posted this query in the wrong section of the forum, I apologise. I wonder too if I've put my questions with too much detail, so I'll post some more concise queries. Does anyone recognise the style of the image view? Any guess at the brand name of the equipment used? What equipment would have been on the market in 2008 that would output a file like this to a USB flash drive? In 2008 were consumer CCTV units linking up to the internet and smart phones like they now seem to? Any thoughts or pointers in the right direction would be appreciated. Thanks