copying DVD,s

[Roy1]

Just a matter of interest. What, if any, is the advantage of using ISO files to burn a DVD when a copy is required, as against using a copy programme like nero or other to copy an existing DVD.

[Mike Shaw]

I think that when you do a copy - with Nero for example - or create a DVD from scratch, it creates ISO files 'behind the scenes' as it were - so when you burn a DVD direct from ISO files stored on the computer, all you're doing is just cutting out the process of saving the files ready to be burned.

Now I'm going to be told, "it's nothing like that at all Mike..."

[Roy1]

MIKE. Interesting theory. However I was wondering that when Nero for instance takes info from a DVD and stores it on the hard drive for copying to another DVD blank, it loses some resolution?. Wheras when creating an ISO from the timeline and then burning to a DVD blank, you are cutting out one generation of copying. I am only surmising of course and most likely am completely wrong in my reasoning. It will be interesting to hear some facts about it from people who know.

[Michael Slowe]

No Mike, I think that you're spot on. When I make a DVD, just prior to the actual burn I end up with a .img file. I then merely drag that file into Toast and burn it to a disc. If I keep that file on the computer I can repeat the process. If however I've deleted that .img and I need a copy of the DVD, I have to insert the DVD into the drive and Toast 'extracts' the file before burning the disc. So, if you still have the .img one stage of the process can be dispensed with. I'm presuming that the ISO files referred to are similar to my .img files. Actually I don't keep my .img files for long as I clear my computer completely between projects. Slightly off thread, I would explain that I save all my films now as ProRes files on separate drives so if I need DVD copies and I don't have a disc available I have to import the file into my edit system and go through the whole process of encoding and making a DVD. That's a pain so I always try and keep a DVD. Same with Blu-Ray but I can't use the .img as that's standard definition. I have to go back to the HD QT .Mov, or copy a BD or, in extremis, go back to the archived ProRes file.

[Mike Shaw]

Thanks for confirming my 'beliefs' Michael! I think that 'img' and ISO files are pretty much the same sort of thing. I'm pretty sure there isn't any degradation in simply copying files - the degradation (if any) comes when transposing from one format to another. When copying DVD's, that is simply file/data copying - no conversion process is involved. When making a dvd from a video file - avi or mov for example - then it is converted (from an AVI to mpg/vob type files for example) and that's where degradation is likely to occur.

It isn't like copying the old VHS videos at all - with serious degradation of quality each time - and the reason is they used analogue techniques. Digital is very precise - a 1 is always a 1 and a 0 is always a 0 (binary wise), whereas with analogue a level of 3.246 for example could be read as 3.2 in an analogue transfer.

If you think about it, a miniDV tape giving an hour of video is actually storing something like 16-17 gigabytes of data in AVI form perhaps. On a DVD, one hour is packed into about 4.7 gigabytes of data altogether - perhaps 4 of those being actual video. In other words, the video is reduced space-wise to about 25% of its original size. Does that mean you get only 25% of the quality of the original? No way!! The space is saved by very subtle means - for example areas of the same colour are 'block saved' over several frames, and so on. The compression algorithms - using digital rather than analogue techniques - are extremely clever these days (the 'codecs) and result in hardly any loss at all. However - if you were to try to squeeze 2 or 3 one hour DVDs onto a single 4.7GB DVD, then you'd see a noticeable reduction in quality. Because the compression needed means real data has to be lost.

Leastways, that's how I see it!

[col lamb]

You guys are right, the process of burning either a DVD or Bluray requires the authoring software to conform the project to fit the standards in place within the software settings, so in reality the software creates all the necessary files in a temp directory and then uses them to burn a disc.

I have just made a short movie and in the hard drive the file is stored in MP4 format at a high data rate which results in a file size of 1.5Gb, now the ISO file for the Bluray complete with menu system is 1Gb

Depending on what my movie content is I tend to store multiple copies, if my movie is to have commentary then I will store a version of the movie without the commentary just in case I want to change the commentary in the future, this way I will still have the background sound set at the correct levels. I then store the finished movie complete with commentary

It is always a good idea to keep a copy of the Image file either the IMG or ISO whatever has been created for future use.

If you want to clear the hard drive then you could always copy the image file to a disc.

In Encore you can add ROM data to a disc and this is what I tended to do in the past before hard drives became so cheap now a large external drive stores all that you do not want on the PC/MAC and is readily accessible..............so now you know what to ask Santa for!

As Mike Shaw indicates digital compressions can be very effective, now a couple of years ago I got fed up with members at my club making movies and putting them on DVD at very low data rates, the end result was avery blocky image during panning or fast movement

I still cannot get my head around why so many take so much time videoing and editing only to produce a visually compromised output all for the sake of decent software. In an attempt to educate I set up a 30sec series of fast moving clips and then produced a series of MPG files with CBR set at 1, then 2 then 3 etc up to 8 and showed them all on one of my techie nights, this is something you may like to try yourselves

[Mike Shaw]

Col - Do you use cbr as a matter of course? I tend to select vbr whenever possible, and I've often wondered, does that yield the best results, really. Also, can vbr be the cause of play-back problems? Never known the answer to that one.

(CBR/VBR = contant/variable bit rate)

Higher bit rates mean more data per picture, which in turn (should) mean better definition/quality.

[Michael Slowe]

Col and Mike. I'll answer this one before our friend Tom jumps in because he and I disagree on this. I use the software BitVice for encoding my DVD;s and they give a choice of VBR or CBR. I always choose VBR which employs a two pass review and in this mode I have to set an average bit rate figure - usually around 6.5 or possibly 7 if the film is quite short. In the CBR setting there is only one pass and you set a definite bit rate. Tom insists that CBR gives the best result but I've been assured by the inventor and owner of Innobits (the Swedish parent of BitVice) that the setting to always use is VBR. My DVD's on the latest version of BitVice are really super so I see no reason to argue about it.

[Mike Shaw]

Must admit way back in the early days of DVD I was 'told' that VBR was the way to go as it tailored bitrate to need - as determined I presume by the first of the the two-pass process. CBR (they said) is a compromise - between overcooking or undercooking at the extremes. (I'm sure that means something to someone! ...). Anyway, as a result of that, I've always selected vbr if I could.

[Dave Watterson]

Just to stick my nose in ... I reckon VBR (Variable Bit Rate) was devised for use with commercial movies that needed to squeeze films of 2 hours and more onto a DVD. Anything which saved storage space was welcome and hence the idea of reducing the bit-rate in scenes where the picture does not change much. The devil, as usual, is in the details. How well does the software process the film to decide where it can reduce the bitrate without harming perceived quality? VBR requires more work from the software creating the file and, presumably also requires extra work from the DVD player.

Since most amateur films are around 11 minutes and darned few of us make movies more than one hour long, it should not be necessary for us to worry about space saving. That's why I reckon it makes sense to use a high CBR (Constant Bit Rate) for our films. I seem to recall Tom suggesting that most domestic DVD players had trouble with CBR higher that 8. That may have changed now.

But as always ... experience is the final decider. Michael's approach produces beautful results on DVD and as a viewer I don't care what my player reports about bit-rates.

And back to Roy's original point ... DVDs can get damaged. Home burned DVDs are more vulnerable that commercial ones. What happens if you need a copy and the only DVD you have is damaged? In that case having an ISO stored away can save the day. On a practical level it also saves a little time ... you can pop in a blank disc and burn from an ISO immediately. Otherwise you waste time reading in from one DVD before burning it to the new one. So ISO is useful.

If you are copying ... make sure you are just copying and not ripping a DVD. Ripping means extracting the files - for example so that you can edit them ... and then when you want to put those files onto a new DVD you have to re-convert the films to the DVD file format which employs compression and does drop the quality. Copying, on the other hand, just makes an exact copy of the files on one disc and burns it onto the new one. No quality is lost.

Dave

[Roy1]

DAVE. Thanks for actually answering my question. You have confirmed my reasoning that there is an advantage to burning an ISO with Encore rather than burning a DVD with the same programme. It's a pity Encore won't burn both at the same time. Still you can't have everything. I know Encore saves a file as an Encore project and a file folder at the same time but I don't know if you can burn a DVD/Blu-ray disc from these. Not that it matters as I am happy to burn the saved ISO made by Encore to a Disc burnt by IMGBURN. I think that to obtain the best quality that some people are obsessed with requires a good quality camera, a good editing programme and a good playback unit. It was the same in the GOOD(?) old days of super 8 film. Some people bought the latest expensive camera and then showed the result on the nastiest cheap projector. It also happened in reverse Cheapest camera, most expensive projector. I'm sure that doesn't happen today though. Sorry to harp back to the dark ages of film but I firmly believe that in those days the result on the screen was really your own work.

[tom hardwick]

I only recommend CBR when the film can fit onto a 4.35 gb DVD-R using 8 mbps. If the film is longer than an hour (say) then a VBR will squeeze and push to make the most of the space available. But get this: if your VBR drops below 8mbps for any reason, then you'll get a reduction in the quality of the picture. So, using a single pass, you'll get the best quality at 8 mbps.

[Michael Slowe]

Tom, that's not what the geek at Innobits tells me. I quoted you on this but he still insists that two passes with VBR is the best way for the highest quality. As you know, the really expensive encoders do hundreds of passes to produce the DVD's that we see of the feature films. Mind you, I've never seen any Tom DVD that's other than perfect, so following his advice can't be all that wrong.

[col lamb]

When I posted about using CBR it was just to make a point about how the bit rate affects the quality and CBR will show up the differences much better.

A DVD has a maximum data rate of just over 9mbps but in reality you will not notice much difference between that data rate and say 7-8mbps in most cases

As Tom says 8mps at CBR will produce a video of great image quality (as long as the source quality is OK), that said VBR (especially 2 pass) will produce a better quality video if the correct settings are used, but a CBR of 8mbps will be hard to fault on all but very, very fast action clips.

The off the shelf Premiere settings are too low and need to be modified to suit, see my VIMEO tutorial on encoding.

When using VBR if the changes from one frame to the next etc are not great the data rate will reduce as the information being recorded reduces, the output quality will not reduce on the completed disc.

If you are making feature films then getting the optimum data rate to enable the disc to be filled is another matter but for most of us making a movie of up to 1/2 and hour optimum data rates go out the window and you encode for maximum quality.

Roy, having a good editing and authoring program makes a considerable difference to the visual quality of the completed movie, I have seen many badly encoded movies that have been made using software where output parameters are fixed. Some people have spent vast sums on camcorders and PC's yet will not spend £160 on decent editing software

Try encoding a few fast paced clips at different data rates and see the resultant effect.

[tom hardwick]

To Michael: two passes with VBR is indeed the best way for the highest quality, but note that I said, 'using a single pass, you'll get the best quality at 8 mbps.'

So yes, single pass is Good
two passes is Very Good
multi-passes is the Best.

But I say that if you have a film that is an hour or less, then an 8mbps single pass gives outstanding quality. Multi passes were designed for commercial releases of long films where 4 mbps is the norm. Play a Hollywood movie with your bit-rate readout in play and be amazed, as I was.

tom.