Bitrates, Quality, and Whatnot ...

MUTTLEY wrote on 5/19/2004, 8:21 AM
The vid I'm burning is only 15 mins long so its not going to take up much space on the DVD between the vid, ac3, and menus. My question as I'm a newb at DVD burning, is what settings specifically could or should I change to increase the quality of the video on the DVD to maximize the wasted space. Doesn't seem worth compressing as much if I don't have to " squeeze " it onto a 80 min DVD.

Keep in mind this aspect of production is new to me, so please be specific. I'm clueless.

- Ray

www.undergroundplanet.com


Comments

johnmeyer wrote on 5/19/2004, 8:51 AM
If you have DVDA 2.0, use PCM for audio, and set the bitrate for your video to 8 Mbs, constant bitrate (CBR). That will give you the best quality available with the DVD standard.

There have been occasional reports that a few players cannot play DVD recordable disks recorded at high bitrates, even though the DVD standard (mpeg.org) specifies that they must be able to handle sustained bitrates of 9.8 Mbit/sec(if you use PCM for audio, then the total bitrate of audio plus video will be pretty close to this). I have not seen one scientific study or test that bears this out, but there are enough anecdotal stories that if you are concerned, you should burn one disk at this rate and then make sure that it plays all the way through on your target set-top player.
bStro wrote on 5/19/2004, 8:58 AM
I keep reading that sometimes VBR can give you even better quality than a high CBR. But I suppose there will never be a definitive answer on that. ?

Rob
MUTTLEY wrote on 5/19/2004, 9:43 AM
When you say " set the bitrate for your video to 8 Mbs " under my mpeg 2 settings constant bitrate is listed by " bps ", by looking at the numbers in the drop down should I set it to 8,000,000 ?

Thanks ;

- Ray

www.undergroundplanet.com

Avanti wrote on 5/19/2004, 10:37 AM
Yes. Go for it!
johnmeyer wrote on 5/19/2004, 1:51 PM
I keep reading that sometimes VBR can give you even better quality than a high CBR. But I suppose there will never be a definitive answer on that. ?

Variable Bitrate (VBR) inreases the bitrate during fast motion scenes and decreases it during slow scenes. Constant Bitrate (CBR) keeps the bitrate the same all the time. Higher bitrates provide better quality for any scene, but especially when there is lots of motion.

The DVD specification permits bitrates up to 9.8 megabits per second (i.e., 9,800,000 bits per second). This includes audio and video. When you subtract out the bits for audio, the maximum for video comes to about 8 megabits per second. If you encode at this maximum using CBR, you will get the best possible quality.

Variable Bitrate will not provide any increase in quality whatsoever compared to CBR, if CBR is done at the maximum bitrate (8 Mbs) permitted by the spec. The place where VBR helps is when you want to fit more video on a single DVD than the approximately one hour that you can get if you encode at the maximum bitrate. In order to get more than this one hour, you have to lower the bitrate. If you set the bitrate to half the maximum, you can get twice the amount of video (two hours) on the disc. Unfortunately, the quality suffers. What variable bitrate does is recognize that if there is absolutely no movement (e.g., a still photo), then you can encode at almost zero bits per second, and the video will still look great. The bits are needed primarily to provide information on movement from one frame to the next. The more motion, the more bits are needed to keep the video from degrading. What a VBR encoder does is look at all the video and use fewer bits during slow moving scenes. It then uses more bits during fast moving scenes. This results in better overall quality, when measured across the entire duration of the two hour video.

Thus VBR only provides quality improvement when you use low bitrates, and only in video material that has some scenes with fast motion and some scenes with very little motion. If you have two hours of video that have almost the same motion in every scene, then you will see very little improvement by using VBR, even at low bitrates.

When you say " set the bitrate for your video to 8 Mbs " under my mpeg 2 settings constant bitrate is listed by " bps ", by looking at the numbers in the drop down should I set it to 8,000,000 ?

Yes. 8 mega-bits per second (8 Mbs) means eight million bits per second which is, of course, 8,000,000.
pb wrote on 5/21/2004, 10:28 PM
johnmeyer is becoming the SPOT of this forum. Thanks for all your insightful, helpful posts, old son.

BTW: what's your opinion of Encore 1.5? We ordered Premiere Pro 1.5 (the Bug fix version the greedy folks at Adobe are charging 99$ for) and I was thinking of getting Encore 1.5 as well. Your thoughts?

Peter
johnmeyer wrote on 5/22/2004, 12:15 AM
Thanks, but Spot is the Spot of this forum. He knows video (and video programs). I only know computers.