MPEG2 Rendering questions

braze wrote on 11/16/2006, 7:00 AM
Please excuse the multiple questions in a single post, but they all seem
related somewhat. I'm switching over from Roxio and trying to grasp my
MPEG2 encoding options.

I have a 13GB (1hour) captured DV (.avi) file, I have done two experiments with,
one was to render it in VMS and use DVDA to build the dvd knowing that it
will not have to re-render it, and the other was to have DVDA do all the rendering.
The results in terms of size of data and CPU time to do the work were very
different.

VMS produced at 2.7GB .mpg file (plus 85MB .ac3), which when built into
a DVD using DVDA yielded a DVD of approx the same amount of data - 2.7GB.
This took 2 hours and 47 minutes on my 1.66ghz computer.

DVDA when rendering the .avi directly, yielded a DVD with much more data,
3.39GB (in this case). I used max of 8mbits for the mpeg2 settings.
This took 3 Hours and 55 minutes, yes over 1 hour longer on same
computer and 700MB larger data.

So my questions..(finally)...

Is size of mpeg files representive of the quality? As with this case, is
the one rendered by DVDA of better quality because it is much larger?
Did I sacrafice quality by using VMS to do the rendering?

Do VMS and DVDA use the same MPEG2 rendering (encoding) engine?

Is there any way to control the VMS MPEG2 options? It is grayed out.
Do I have to upgrade to professional version to get that capability?
(my software link shows that would cost me $425 - ouch - that is alot
for something all the other entry level video editing software packages
have).

Does anybody know what the compiled in settings are for the VMS
main concept MPEG2 encoder are? eg. max bit rate it uses?

Clearly VMS was much faster at rendering this 1 hour example, but
I'm concerned I have sacrificed quality and not sure how I can make
VMS use a higher quality setting if that is desired.

Thanks for any info.

-Braze



Comments

IanG wrote on 11/16/2006, 9:47 AM
>Is size of mpeg files representive of the quality?
Yes, ish! The size is related to the bit rate, and higher bit rates should mean higher quality. However, if you can't tell the difference, then there's no real qualitative improvement. A lot depends on your source material - if you've got lots of movement and lots of detail you need the high bit rates.

>Do VMS and DVDA use the same MPEG2 rendering (encoding) engine?
I believe so.

>Is there any way to control the VMS MPEG2 options?
Not in VMS, no.

>Does anybody know what the compiled in settings are for the VMS main concept MPEG2 encoder are?
Probably, but it's not me, and I don't have VMS installed on this PC. From memory, I think VMS is using a fixed bitrate, but I can't remember what it is. There are apps which will analyse a MPEG and give you the max and min bitrates used if you can't get a definitive answer.

Ian G.

davdee wrote on 11/16/2006, 5:05 PM
While I have not personally tried it, I was told that Vegas should always do the renders to MPEG from AVI rather than let DVDA do it. The former has a better codec than the later.

Whenever I use DVDA, I use VOB/whatever file previously rendered from VMS, so all DVDA has to do is worry about the menus/etc and the final burn.