Avoiding recompression

Jack S wrote on 3/4/2011, 12:39 PM

I read in a previous thread that to avoid the possibility of DVDAS having to recompress a project after it had been rendered by VMS I had to use the Make Movie wizard instead of 'Render as'. I've just used the wizard to render a 1hr 56m project consisting of some PAL AVI clips but mostly NTSC MPEG clips using the DVD option. When I passed it on to DVDAS the size was about 5.2Gb. I must have done something wrong but I can't think what.
I've just realised that the project properties are PAL DV. Could this be the problem?

Comments

Chienworks wrote on 3/4/2011, 12:56 PM

I would say that the 'make movie' wizard is probably one of the worst choices you can make. There's absolutely nothing that does that you can't do, and do better, with advanced render.

DVD Architect wants the video as MPEG2 with AC3 audio in a separate file. Using Advanced render you can create these and tweak various settings to get the size just right (Version 10 only, version 9 and previous didn't allow setting bitrates).

Note that the only thing you did wrong when getting a 5.2GB file was to use too high a bitrate for the video. You have no option to change that with 'make movie', so that's one of the reasons why it's a poor choice. To fit 116 minutes on a standard DVD the video bitrate should average about 4,970,000. 'Make movie' defaults to 6,000,000.

Jack S wrote on 3/4/2011, 2:41 PM

Thanks Chienworks. That's solved the problem.
One more thing. How did you come up with the bitrate figure for 116 minutes. Is there a simple calculation I can do in future so I don't have to spend hours of render time experimenting with bitrate settings.

Thanks in advance.

Chienworks wrote on 3/4/2011, 2:49 PM

There's a very super-simple one that's quick and easy and close enough to be useful pretty much all the time.

Divide 600 by the length in minutes to get the combined audio & video Mbps value.

600 / 116 = 5.172414

subtract about 0.2 for the .AC3 file, assuming you're using 192Kbps.

5.172414 - 0.2 = 4.972414

Multiply that by 1,000,000 to fill in the blank in the MPEG2 custom settings window.

This usually gives me a result that fills 98% of the disc, leaving just a nice amount of room for a title screen and menus.

Jack S wrote on 3/4/2011, 3:37 PM

Thanks Chienworks. That's great. You're a star.

Thanks also for your prompt response to my first post.

OhMyGosh wrote on 3/4/2011, 9:17 PM

Thank you too Kelly for the magic formula :) I had it put away somewhere on my old computer, but long gone now..... Very few of my projects are longer than 15 minutes, could the bit rate ever be too high, or just always go for max if it will fit? Thanks. Cin

MSmart wrote on 3/4/2011, 10:19 PM

Cin, the max bitrate you can do in DVDAS is 8Mbps so just leave it at max and don't have to worry. Only when they approach 1hr do you even have to think about it.

Kelly, let me ask you, which MPEG encoder is better, the one in VMS or DVDAS?

As you may know, I use DV-AVI video and always render to DV-AVI then use the Fit To Disc feature in DVDAS to use the needed bitrate to make the project fit on the DVD. It's easy but should I rethink my work flow? I've always been happy with the results so I think not but will reconsider if your reply is compelling.

Chienworks wrote on 3/5/2011, 4:44 PM

Both Vegas & DVDAS use the same encoder. The difference is that in Vegas (at least version 10) you have the ability to tweak all the custom encoder settings. DVDAS doesn't let you do this. So if you're trying to fit something rather long on a disc it's better to render MPEG2 in Vegas just so that you can choose the settings you want.

Minor point, but it can make a noticeable difference now and then. DV is 4:1:1 color and MPEG2: is 4:2:0. I won't go into a long discussion of what this means, but full color is 4:4:4 and anything less than that means that the encoder throws away color data to help with compression. So if you render to DV first, then to MPEG2 from that DV file then your result is 4:1:0. You lose some color resolution and data both ways and the result is cumulative. For original DV material it's not very important because it's already 4:1:1. However, if you've add photos or text or overlays or made heavy use of color effects then the extra conversion can be noticeable.

MSmart wrote on 3/5/2011, 5:59 PM

I'm fine then, thanks. I render my multi-cam DV video to DV in VMS, bring the DV into DVDAS and let it calculate the bitrate needed so the mpeg2 (vob) files fit the disc.

OhMyGosh wrote on 3/5/2011, 8:28 PM

Thanks MSmart. :) Cin