DQ: Must video & audio be the same length?

JimMSG wrote on 12/18/2007, 7:40 AM
Working on a DVD project for a client. The editing is really finished, the client used Vegas Movie Studio or one of the other Vegas home versions with .vf files and .dar's I could load right into Vegas 8 and DVDA.

There are three sections to the project. The first two the client completed, but couldn't make the third section work. Section one is just under six minutes, section two is an hour forty, and the reason he couldn't get section three to work is it is 17 seconds short of six hours.

The client would like to get this all onto one DVD. I've heard it is possible to get nine hours onto a DVD-R, and outside of the first section, all of the video is scanned photos and picftures. He did a little pulling and closing with them but it really is more of a slide show than a video.

In addition, the six hour third section has only about three minutes of pictures in it. The rest of the six hours is audio only. I was thinking perhaps I could just render the video from the three minutes there is actual video for, that could save a lot of space on the DVD and could reduce the amount I would have to lower the VBR rates. But, can I render the entire audio as an AC3 file and have it play in its entirety from a DVD without having a video file the same length?

Of course, then the next question is going to be, if I can make it work this way, how do I calculate the VBR? Using just the overall running time of the video wouldn't account for the much longer than normal audio file accompanying it. By the same token, I want to keep the rate as high as possible to preserve as much of the original quality as I can. Some of the slides are old, yellowed, family documents.

Suggestions?

Jim

Comments

Chienworks wrote on 12/18/2007, 10:29 AM
I'm pretty sure that DVDA is going to use the length of the video to determine the length of that section.

I'd split that last section in two: a three minute section with audio and video, then the rest of the audio as the fourth section. Even still the fourth section is going to have video with it. If nothing else, DVDA will create an MPEG file with all black frames. Not sure how you can coax it into compressing nearly 6 hours of that down to fit.
nolonemo wrote on 12/18/2007, 11:29 AM
Well, if you're using Vegas 8, I'd try splitting that last section into the video+audio and audio only portion, and then rendering the audio only portion as separate video and audio files with a mimimal bitrate on the video file. You want to be importing fully rendered assets into DVDA so it isn't going to be doing any re-rendering.
Chienworks wrote on 12/18/2007, 1:06 PM
Vegas only allows a minimum bitrate of 400Kbps for MPEG2 video. So that means that even with just a solid black track, the video portion of the audio-only section is still gonna weigh in at about 1GB. That doesn't leave much room for everything else.
nolonemo wrote on 12/18/2007, 3:51 PM
Here's the way I calculate it. Project has 6 hours of audio and 2 hours of video+audio. The 6 hours of audio at 192kpbs stereo AC3 comes to about 500MB or .5GB. The black video for the 6 hours of audio-only comes to 1 GB, so you've got about 2.8GB left for the 2 hours of video + audio. You'd need to encode the video for that (assuming 192 for the audio) at around 3100kpbs. That's low, but it could be done...not sure how good it would look, the good news is that it sounds like you don't have movement in the video, which helps.

For bitrate calculations, I use Vcalc.exe, a free download at dvdrhelp.com and elsewhere. By padding the number in the "space for extra files" box you can figure out the bitrate for each segment.
Chienworks wrote on 12/18/2007, 6:45 PM
If it's any compensation, that 6 hours of black ought to render *very* fast!
JimMSG wrote on 12/25/2007, 4:51 PM
Got it all done in time and on one disc. Splitting the big file between video and non-video segments made the difference. Found out a couple of interesting things in the process. For example, I did a couple of short five minute test renders. For one I put in a constant bit rate of 192K, lowest allowed in the "Custom" render dialog, and for the other I did a VBR with 192K for max, min, and average bit rates. I was expecting the size of the files generated to be the same, but the VBR was significantly smaller than the CBR file even though the bit rate was the same throughout.

Another thing I noticed is if you split a file like this using "loops" and rendering the loops, the remember project markers doesn't work. I don't know if it was because I was rendering a loop only, or if it was because the first marker in the loop was number 2 not number 1. Had to have chapter marks though, so I put them in by hand and learned another interesting tidbit.

The timelines in V8 and DVDA don't match. The length of the track in V8 is 5:54:07.24 and in DVDA it is 5:53:46.17. I don't know if this is a function of the two programs or the rendering (I do all of my rendering in V8 using Pro AC-3 for audio, haven't a clue what the difference is between the two AC-3 formats, but Pro has that "must be better sound to it and mpeg2 for video) but it made locating all the chapter points a little more exciting. I had expected to locate them by going to the same time on the DVDA timeline as the marker on the V8 timeline. Doesn't work that way though. Not sure if this is an issue that needs to be fixed or not.

Regardless, thanks for the assistance and I hope you and your family had a truly Merry Christmas!

Jim