Modifying DVDs

[Tosh McCaber]

I'm successfully using Pinnacle Studio to transfer my DV tapes, edited, onto DVDs. This should enable me to re-use the original tapes, which have become numerous.

My question is- can anyone say whether I can, if necessary, carry out re-editing on any of the DVDs that I have created. For example, if I find another tape with similar subject matter, that I may wish to insert into the original DVD, I think that I can add it to the end of the DVD.

But, is there a way of re-processing the DVD, so that I can add additional material into the middle of the original material, or edit out parts that, in retrospect, I don't want from my original burning?

[BRL]

Hi There. Not sure if this is what you mean but do Pinnacle, at the end of burning, offer you to keep the disc 'open' or close it?

[Tosh McCaber]

No, BRL,

So far as I can find, there is no option for that, such as you would have in Nero, Roxio, etc., other than creating a virtual image, that could be burned later with a commercial programme, such as Nero.

Even then, my query relates really to being able to "re-edit” the disk in the middle of the content, and produce a new disk with content added or deleted, rather than adding on to the end of it.

As an aside, I'm not overly impressed with Pinnacle's "aftercare" service. When I phoned about this, I was informed that I would be allowed one free call to them, if I quoted an obscure number (not the serial number), which may have been on the the CD sleeve or the box, and which I certainly could not find!

[Background Noise]

The recorded product is not the same format as the original tape. Actually its all ISO and VOB stuff on the DVD but you can rip that into mpg and re-edit that.

I keep all my original tapes so that I've got it if required. I also save a copy of my production back to tape, so that is what I would re-capture later to re-edit. Also when you create your DVD film you can create a high (DVD quality) mpg file as well and save that on a disc.

If you want to free up the tapes (actually they aren't that expensive now) just downlaod the video into the standard avi files that pinnacle creates and save them as raw avi to DVD discs. If it's really important stuff make 2 copies.

[criticalmass]

I'd be wary of how many times you re-use your digital tapes.

In broadcast work, re-using tapes is done very few times, due to signal-to-noise problems as tapes are re-used, and as they age. This was as true of analogue as it is of digital.

For analogue broadcast master tapes, every pass through a tape machine was logged, and after a certain number of passes the tape was scrapped. Metal tapes are abrasive, and the head-drum of a Betacam SP unit (say a Sony BVW-75) slams the video head into the tape at a pressure approaching 1 tonne per square inch. Only the boundary layer of air between head and tape prevents massive tape damage. Machines in heavy service (on-air machines) were fitted with sapphire blades in the tape path to physically scrape the tape surface and remove any dust or particulate contaminants to prolong head-drum life. Biggest damn sapphires I've ever seen, they looked like like small chisels!

The situation isn't all that different with digital tapes, but instead of signal-to-noise problems, you get error-correction problems, where errors begin to multiply to the point where the error-correction algorithms are unable to cope - and a pixellisation (or "blocky" )artifact rresults. The audio can also glitch (usually a click) at the same time - or possibly later - since audio and video are multiplexed together and then written to tape in a scrambled manner to minimise the effects of slight tape damage in any one area by (hopefully) spreading it throughout the frame instead of displaying it in a single line of the scan.

OK, so you decide to re-use your digital tapes. Now, if you keep going through the process of going from DVD back to AVI and then do your editing, then re-rendering to MPEG to burn to DVD, the pictures slowly but surely degrade. One problem is "quantisation noise" and it's inherent in digitisation of video. I did a production recently where I had three generations of DVD on the finished cut - and the noise on playback was so objectionable I went right back to camera-tapes (shot with a Hitachi 3-chip Z*ONE DA digital broadcast head with Fujinon 14X EFP lens) and re-cut the whole thing from the start.
The end result was significantly cleaner pictures when the final DVD was played back, so the effort was well worthwhile. I am fussy about picture quality because I charge money for it.

How many generations you can go depends entirely on what image quality you are prepared to put up with. My clients pay for clean pix, and that's what they get, even if it means I have to go back to the beginning and re-cut the whole production. If I have a rough-cut to work from it can be a very fast process, and you get to tidy up anything you were less than 100% happy with, especially audio-wise. Audio is 10% of the shoot and 90% of the problems in the edit-suite.

If you get the impression that digital video isn't without problems, you are quite right. In the early days I well recall a salesman saying "you can have up to fifty generations of editing without loss of quality" whereupon I replied "If my editor needs fifty generations of editing to achieve an effect then I'll be looking for a new editor!". He didn't see the point.

Never lose sight of the fundamental truth of digital video:- "Going digital is the end of all your old problems - and the beginning of all your new ones, and some of them are worse than the old ones!"

[Tosh McCaber]

Thanks, CM, That's good info.

I must say, that Pinnacle Studio appears to finalise the disk, rather than, as you can do in Nero or Roxio, create a session, where you can add more material at a later date, albeit to the end of the previously recorder material.

Coming back to my original question, so I've transferred to a DVD from the original tape, after editing. However, is there any way that the contents of the DVD can be thereafter transferred back onto the pc, and re-editted and new material inserted? (Sadly, I think not.)

Tosh

[criticalmass]

I don't know of any "ripping" software that will enable you to copy MPG2 files off your playable DVD (although they're stored as Video Object files, or VOBs, they're MPEG2 underneath it all), edit (staying in MPEG2) and then re-author into UFO, BUP and VOB files and re-burn. Trying to stay entirely within MPEG2 is a major pain in the a@$e.

If you play your DVD into a PC via a video capture card, then you've now gone one generation further in the edit because the capture card probably doesn't capture MPEG2 but the (now) de-compressed file. So already it has been through MPEG2 and back again.

If the bit-rate the MPEG was originally encoded with is high (say, video bit-rate above 8Mbits per sec), it may withstand a further generation (MPEG2 back to AVI, editied, then re-rendered back to MPEG2, re-authoring and burning) and still look OK. However, you will be adding the second generation's quantisation-noise to that of the furst, and sometimes this noise may be visible in the picture - depending on how good your display device is and how finicky you are about picture quality.

MPEG2 is heavily compressed, and the process is pretty technical, involving initially a lossless digitisation process of an 8X8 pixel "macroblock", then quantisation and compression of the digitised data using a numerical matrix and a Discrete Cosine Transform function. This compression is lossy, but the losses are in the finest details as far as possible, relying on the inability of the human eye to notice the difference - and the usually mediocre resolution of domestic display devices.

MPEG2 further reduces bandwidth (or filesize) by having three different types of compressed picture frames. The I-frame is a complete, displayable frame of video, entire of itself. The B-frame is a bidirectionally-predictive frame, which contains information as to motion vectors for frames that precede it and follow it (naturally these frames have to be transmitted out-of-normal-time-sequence so the motion vector determinations for frames that should be displayed prior to the B-frame that contains their information can be correctly displayed,) and the P-fame, which contains information about the frame which follows it in normal time-sequence. (I work with this stuff all the time and it still makes my head spin too!)

In satellite transmission, we use a Group Of Pictures (GOP) as follows: IBBPBBPBBPI, so an I-frame occurs only every so often - and if the MPEG2 decoder loses lock, then it has to wait until an I-frame arrives in order to re-lock to the transport stream and begin correctly reproducing piccies again. I-frames are largest in terms of bits, P-frames are smaller and B-frames are also small, thus maximising efficiency and reducing transmission bandwidth requirements for any given video bit-rate.

DVD MPEG2 seems to prefer to use only I and P-frames, allowing DVD MPEG decoders to re-establish frame-sync much more quickly, reducing the visual impact of a glitch. This increases filesizes for DVD Video Object Files.

Forgive the technicalities above, but what I'm trying to show is that repeated trips through the MPEG2 process back to uncompressed video, then back into MPEG2 etc etc etc just erodes picture quality, although the degradation for a second generation may not be noticeable - it would certainly be worth a try. All you'll lose is your time and possibly a single DVD at the end of it all if you're not happy with the result.

The microprocessor power necessary to edit entirely in MPEG2 would be truly massive, and there is the added burden or overhead of correctly reassembling the B and P-frames into correct order to successfully edit in MPEG2...which is almost like de-compressing the video anyway. I don't know of any editing software that works entirely within MPEG2 files, most of the professional stuff prefers to work in uncompressed video, so transitions etc can be previewed instantly instead of needing to be re-rendered into a new MPEG2 group of pictures and re-muxed into the data stream.

Basically, editing in uncompressed files is faster and allows the original material to remain unaltered, as all the editing software us really doing is buildng up an "edit decision list" which is then executed on the files as needed at rendering-time, before the uncompressed video is turned into MPEG2.

Don't know if this is really the answer to your question, but at least it may help you to understand the horrendous things that have to be done to beautiful analogue PAL or NTSC (or SECAM) piccies to crunch them down into DVD files, and why we infinitely prefer to work in uncompressed files in the edit process, which in turn explains our reluctance to re-use camera-tapes. If a production has to be extended, shortened or re-edited, it is by far the best option to have the original camera-tapes and go back to them. They are the best it is ever going to look, and everything after that is a slow trip downhill.

Speaking of "how good it looks", even the best digital handicam of today won't shoot piccies that look any better than those shot on ten-year old broadcast camera. Even an old analogue broadcast camera will have a magnificent Fujinon or Canon lens, built with something between 14 and 18 elements, designed to be superb in resolving-power, tack-sharp, free of distortion and costing probably five times what a digital handicam does anyway. Right at the back of the lens is the best the pix ever look, and a good lens is the greatest ally a cameraman has to get decent pictures - and always will be. I still shoot on Betacam SP (an old analogue broadcast format) which is playable in any digital Betacam deck. Once the pix are on a hard-drive, what tape format they were shot in is immaterial. How good the lens was is still important because that basically determines how sharp the pix will be and that doesn't alter much afterwards until you get to very low bit-rates - far to low to be useable.

Another issue with DVD files is the actualy playable files (Video Objects or VOB files) are seamless, that is one ends precisely where the next begins as far as playback is concerned, so it is essentially seamless when menu-driven DVDs are played. (Each separate menu-item requires a separate VOB file).

Altering the length of any one VOB file within a group will require complete re-writing of all the subsequent VOBs as well. Again, I don't know of any software that does this at the editing stage because VOBs are not editable as such. They are the result of DVD authoring software chopping up an MPEG2 file into chunks to suit the playback requirements of the DVD player. (The largest a VOB can be is 1Gb, so a DVD of any length will have several VOBs.)

Basically, play your DVD back into your PC via your video capture card, add your new material into it, then re-render and burn a new DVD. That's what I would do, if I didn't have original camera-tapes to work with. If I did, then I'd always go straight back to them and start again.

Apologies for a long and technical post, but if a little knowledge is a dangeourous thing, a lot can be positively addictive!

[spannersatcx]

I have a feeling you can in ulead dvd studio. Have a look at their website to check though.

I'm pretty sure I've done it when Pinnacle was unable to. In fact after a recent holiday I captured my DV tape and added in the footage from another dvd that was made of the Mrs and Daughter on a Camel trek by the camel man! Just combined the tape and video files from the DVD. Worked OK.

[criticalmass]

Tosh McCaber,

Have a look in the "edit" section of www.videohelp.com website. There are a wealth of articles and one or more may well have all the information you are looking for. A very informative website.

[Tosh McCaber]

I've been away.

Thanks to all for your helpful replies.

Tosh