Bitrate Calculators and Min/Avg/Max Bitrates

rcartaino wrote on 4/20/2009, 12:25 PM
I am using a video bitrate calculator to determine the bitrates (two-pass, variable bitrate) to get the best quality on a single-layer DVD. I have a few quick questions:

1. Shorter videos - If my video fits easily on a DVD (say, 20 minutes or so), is it better to switch to a constant bitrate and set it for maximum quality for the entire length? Or, is there some advantage to sticking with VBRs, regardless?

2. Max bitrates - But my bitrate calculator (as well as Sony Vegas Pro 8) typically suggests “max” settings in the 9,500 to 9,800 Kb/s range. Most forums suggest that video bitrates should not exceed 8,000 Kb/s to avoid “stuttering” on some DVD players. If I change the max bitrate (should I?), how would I re-calculate the minimum bitrate to compensate? (I’m assuming the “Average Bitrate” should always be the same as the equivalent constant bitrate (CBR) calculation).

Thank you.

Comments

John_Cline wrote on 4/20/2009, 2:48 PM
1) If you're using a single-sided DVD and your video is under about 72 minutes, then CBR at 8 Mbps is fine. There is no advantage to VBR over CBR when the video will fit at 8 Mbps.

2) Recalculating the minimum bitrate isn't really necessary. Just go ahead and reduce the maximum to a "comfortable" level, leaving the "Minimum" and "Average" bitrate alone.
craftech wrote on 4/20/2009, 3:18 PM
For videos an hour or under use John's CBR recommendation of 8000.

For videos over an hour and up to around an hour and 20 minutes I use:
a 2-pass VBR
Average 6750
Maximum 7500
Minimum 2700

Looks good with either Vegas or Procoder 3.

John
rs170a wrote on 4/20/2009, 4:39 PM
John (craftech), I think your numbers are on the conservative side.
The bitrate calculator I use (note: the link is to a zipped file - thanks to John Cline for hosting it) gives me the following settings for an 80 min. video:
Max: 7848
Avg: 7136
Min: 3568

Mike
craftech wrote on 4/20/2009, 5:04 PM
John (craftech), I think your numbers are on the conservative side.
The bitrate calculator I use (note: the link is to a zipped file - thanks to John Cline for hosting it) gives me the following settings for an 80 min. video:
Max: 7848
Avg: 7136
Min: 3568

Mike
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With menus? The bitrate calculators seem to cram a lot onto the discs I have found, but I don't think those settings you posted would result in a much different looking video. Maybe?

John
rs170a wrote on 4/20/2009, 5:11 PM
Yes, with menus.
I set Fixed menus to 20 and Menu Transitions to 10 and still got the same numbers.
Your Avg. bitrate (the one that matters) was 6750 compared to mine at 7136.
IMO, this should result in a better looking video.
I'll leave it to experts like John Cline to confirm this.

Mike
John_Cline wrote on 4/20/2009, 8:36 PM
I'm posting this on my phone, so I can't check the numbers. Programs like Vegas deal with bitrate in bits per second. Programs, like Procoder, deal with bitrate in kilobits/second. The bitrate calculator hosted on my web site will do either. 8,000,000 bits/sec in Vegas = 7812.5 kilobits/sec in Procoder.