optimize disc default bit rate

Gabonviper wrote on 10/3/2012, 1:58 AM
Hi,
I tried to find the answer to the following in the DVDA manual, but still a little baffled, so...

I am now about to finalize my blu-ray disc (rendered in Vegas Pro 11 using the 1440 60i 25 kbs template (changed the max-ave- min bit rates to 40 25 25), and was wondering if the default bitrate setting 18,000 in Optimize Disc in DVDA only affects recompress situations. DVDA seems to accept the modifications I made in the max-min bitrates in Pro 11, so there shouldn't be any recompression. In the project propertiesin DVDA the bit rate is 18,000 (the default), while in Optimize Disc the max bit rate for the rendered video file is 48,000.

Should I raise the default bit rate in project properties/optimize disc?

Comments

Steve Grisetti wrote on 10/3/2012, 7:48 AM
The optimal bit rate for video on a BluRay is 18000. Manually adjusting the slider beyond that will increase the file size on the disc but with no improvement in quality.

That 48000 rate sounds more like the sampling rate for the audio.
musicvid10 wrote on 10/3/2012, 8:42 AM
You don't want to recompress your files in DVD Architect, period. It wastes time and degrades quality.

Use a bitrate calculator. Use an average bitrate in Vegas that will fit your disc, the first time.
Your bitrates are nonsensical. Setting the average and minimum bitrates the same is the same as Constant Bit Rate (if it can't go lower than 25, it can't go higher, can it?).
Gabonviper wrote on 10/3/2012, 10:04 AM
Musicvid:

I am puzzled by the variable bit rates in Vegas:

The default render settings in Vegas pro 11 and 12 offer the variable bit rates max 30,000 average 25,000 and min 20,000 kbs, saying:
"Constant bit rate
Select this radio button and choose a setting from the drop-down list if you want to encode your file using a single bit rate.

Variable bit rate
Select this radio button if you want the encoder to vary your file’s bit rate to accommodate high- and low-motion changes in video. Variable bit rate files can produce higher picture quality and smaller file sizes than constant bit rate files."

I am using a 50 gb bluray disc for 3:02 hrs of video, and it should fit fine. DVDA also seems to accept the settings (even if I change the max to 40 from 30,000) as there is a green tick next to the file in the optimize disc section and "recompress: No" (the same with the default variable bit rates).
Doesn't this then mean DVDA will not recompress or rerender the file?

I have noticed that if I use lower bitrates image quality will not be as good as the default variable bit rates offered by Vegas in the template. So should I just set the minimum to 20,000?
musicvid10 wrote on 10/3/2012, 2:02 PM
Again, your average bitrate must be such that your file will fit on your disc.

Bitrate x Time = File Size

Nothing magic here, it's basic math.

Variable bitrate is much more efficient than Constant, because it lowers the bitrate when it doesn't need it, and raises it when it does. So in order to work, the average bitrate must be between the minimum and maximum. Just "what" any of those values should be, I have absolutely no idea, because I don't know anything about your source video. Use a bitrate calculator, experiment, and good luck.

If you need more information about variable and fixed bitrates, Wikipedia is your friend.