Does Re-Rendering Loose Quality ?

pmc181 wrote on 12/27/2002, 8:50 AM
I just got a HP 200E DVD writer and wanted to see the difference between the quality of SVCD'S that I've been making and DVD'S. However, I didn't have the avi or veg file from my last SVCD project. All I had was the mpeg2 I made. I brought it back into Vegas and used the default DVD template and then burned my DVD movie in Sonic MyDVD program. Everything works including menus, but the quality looks the same.

Is it okay to re-render an mpeg2 or do you loose quality, or should I have tweeked something in the template ?

Thanks All
Paul/Magnum Blues

Comments

SonyEPM wrote on 12/27/2002, 9:23 AM
Re-rendering MPEG source files will always result in degraded quality, no way around it. Your best bet, for the smallest possible quality hit, is to open the MPEG in vegas, render to (ideally) uncompressed avi, do your edits, titles etc, then render back to MPEG.
Chienworks wrote on 12/27/2002, 9:24 AM
Since you were re-using the MPEG that you made for the SVCD, you in effect were putting SVCD quality onto the DVD disc. Once quality is lost you can't get it back. To get the good DVD quality, you'd have to start with the original material again.
JohnnyRoy wrote on 12/27/2002, 9:32 AM
To answer your question: re-rendering will loose some quality when using a “lossy” codec. Since MPEG is lossy, re-rendering an MPEG will degrade the quality. If you use a “loss-less” codec or use “uncompressed” video (i.e., no codec at all) then re-rendering will not loose quality.

The reason you did not see improved quality is because re-rendering cannot create quality that wasn’t there in the first place. Your target will never have better quality than your source (hence the old adage, “garbage in, garbage out”). This, of course, assumes you are not filtering the source to improve it by removing noise, etc.

You won’t see a difference until you start with a new AVI source and you’ll definitely notice that the DVD looks just like the source while the SVCD will show some compression artifacts due to the lower bitrate.

It might be a good idea to back up your master videos to DV tape as well as DVD. This way if something happens to the DVD (i.e., left in the sun, sat on and cracked, lost, etc.) you could just recapture the DV AVI and re-burn. Had you done this with your SVCD’s you could have made high quality DVD’s from the master tapes. Doesn’t help you now, but its something to think about going forward.

~jr
pmc181 wrote on 12/27/2002, 10:57 AM
Thanks Johnny and all of you.
Question for you Johnny since you mentioned DV tape. What is it? I have a Audio hard disk recording studio that started out using the Alesis Adat system. I've read a lot of posts where people mention about going to or from tape.

Is it cheaper/easier to store on some type of tape sytem because of how large AVI files are, or are they talking about storing it back on the tape in the camcorders ?

Thanks,
Paul
seeker wrote on 12/27/2002, 3:43 PM
Paul,

"Is it cheaper/easier to store on some type of tape sytem because of how large AVI files are, or are they talking about storing it back on the tape in the camcorders ?"

DV tape is indeed the tape that is used in the digital camcorder, if your camcorder uses the DV digital format (either MiniDV or Digital8). It wasn't clear from your message what your original video source was. Be aware that the DV format has already done a 5-to-1 compression, and that losses have already occurred in the camera itself in order to compress 4:4:4 information into the 4:1:1 DV format.

But Vegas in its present form is essentially a DV editor. There have been requests to expand the scope of Vegas' editable video formats in the future, primarily with an eye toward HDTV editing. But for the time being we can consider DV video as "pristine" and a good lossless way of storing DV video is back to DV tape.

It is debatable whether DV tapes are more secure than DVD discs. The tapes are subject to stretching, polymerization hardening, oxidation, oxide shedding, and mechanical wear, while the discs are subject to delamination, scratches, and dye fading. I think it is quite debatable that there is or has ever been any archival form for video.

Another thing to consider is the sheer size of DV files. Even with the 5-to-1 compression, they are still very big in that 4.5 minutes of DV video require a gigabyte of storage. Since a regular DVD-R holds only 4.7GB you will get a little less than 22 minutes of DV on a DVD-R, while a DV tape will get a little over 60 minutes without resorting to the high-capacity DV tapes. The relatively higher capacity of the DV tapes is an obvious advantage.

I think the coming blue laser technology discs, with capacities of maybe 100GB or more, may shift the size advantage to discs. But that technology is a few years down the road. Hopefully it won't be too long in coming, because the capacity demands of HDTV editing will certainly need them. And hopefully Vegas 5 will be fully HDTV capable by the time HDTV camcorders come down into the prosumer/consumer range.

-- seeker --
pmc181 wrote on 12/27/2002, 6:37 PM
Excellent post Seeker. Actually, we have only a Sony Handycam analog 8mm camcorder. But we want to buy our first digital camcorder and I'm leaning towards a D8 model to be able to use all of our old analog 8mm tapes also. Although,we could go either way, D8 or minidv. I want to make a smart informed decision though on a camcorder that will give us the quality we want and still in our price range. As we keep learning, we want to do high quality DVD'S and 5.1 surround sound.

Any suggestions for the minimum specs for a digital camcorder that would give us excellent resolution ?

Thanks,
Paul/Pat Magnum Blues
Tyler.Durden wrote on 12/27/2002, 8:14 PM
Hi Paul,

FWIW, I have a D-8 handycam, specifically to have the backward-compatibility with 8mm and Hi-8 while also being able to shoot and edit in the same codec as DV.

The D-8 handycam works great with Vegas and has all the features of DV except the LP mode, so 60min is the longest load I can run. It also serves as the convertor from analog to DV and vice-versa.

On the subject of archiving, D-8 and DV tape should be stable enough for the time it will take to develop a storage-medium that truly lasts... At least with digital you can always dub to newer stock with no loss, provided you do it before the medium falls apart.


HTH, MPH
JohnnyRoy wrote on 12/28/2002, 10:56 AM
Paul,

Seeker beat me to it, but yes, I was referring to miniDV or Digital8 tape (sorry) and I made an assumption you had a DV camera as your source, which you don’t.

As for a recommendation on a camera, since you already have Hi8 I think Digital8 is probably a logical upgrade. I came from VHS-C so I selected miniDV. Digital8 cameras are cheaper than miniDV so you’re in luck. I don’t think quality will be an issue as the cheaper digital cameras within a given manufacturer usually have the same quality as the more expensive ones (assuming a single CCD and the same optics) and it’s the extra features that determine the price in a product line.

For example: I bought a Panasonic DV-601 which had the same CCD and optics as the DV-201 and DV-401 but was a few hundred dollars more because of the extra features I wanted. For me, having analog inputs and a manual focus ring was key. Be careful that the manual focus is not buried in a menu somewhere where you can’t get at it when you need it. (‘cuz you know you need it when someone walks in into your field of view and you need to quickly switch it on and adjust back to what you were shooting)

My biggest advice is to think about the features you can’t live without and make sure the ones you need to access quickly are buttons on the outside of the camera and not buried in the menus where they are useless. Don’t assume that because a camera lists manual white balance or iris on its specs sheet, and your analog had it as a switch on the outside that a digital camera will too. That’s where the manufacturers cut corners and burry features in the menus. Menu features are for things you use infrequently or can set up before a shoot. Be careful and make no assumptions.

Marty mentioned, “...It also serves as the converter from analog to DV and vice-versa.” Don’t overlook this. Try and get a camera that has an analog input. (I think they all have analog outputs). This will let you capture VHS tapes through your camera to your PC. You never know when you might want to edit a VHS tape or two. Of course, if you get a miniDV camera with an analog input, you could also capture your Hi8 tapes through it so don’t think that Digital8 is your only option.

~jr