CBR vs. VBR

[vcdhelppos]

as for the quality of the video, does VBR encoding produce better quality than CBR? or does VBR just give you smaller size files than CBR? or does VBR produces both, better quality and smaller size files?

also about cutting mpeg2 and raw AVI files. I know some people that cut mpeg2 files that are in the 4GB size or larger, sometimes have audio sync problem. what about cutting AVI files, do they normally have audio sync problem? basically, what are the common symptoms for both file types?

thanks.

[ZippyP.]

At lower bitrates VBR will give better quality than CBR and at high enough bitrates it does not matter. So VBR will preserve quality and allow smaller file sizes.

Mpeg is more of a finished product so sync problems are typical when you edit with it. Avi is much more forgiving and editing/cutting is usually done with it, then conversion to mpeg if that is the desired format.

[vcdhelppos]

zippy,

I'm converting my home video at 9200 bitrate using TMPGEnc Xpress 3.0. This is the default setting. Is this too high? I see that there is a maximun option checkbox to cap it at 8000 bitrate.

I converted a 31 mins video using the default 9200 bitrate and it made a mpg2 file of 2.1GB. so an hour of video would be about 4.2GB that would fit on a DVD-R media.

Does anybody know if there is much quality differences between 8000 vs 9200 bitrates? What is the standard bitrate for DVD movie that you buy at the store?

also zippy, what is the lower range of the bitrates for VBR that you mentioned to have better quality than CBR?

thanks


my system configuration:

DELL 8300 series ($860 after a $150 mail in rebate)
P4 3.0Ghz HT 800 FSB
1GB of Dual Channel ram 400Mhz PC3200
40GB IDE Hard drive 7200 RPM
Nvidia FX 5200 with 128DDR
8X DVD burner

[disturbed1]

Does anybody know if there is much quality differences between 8000 vs 9200 bitrates? What is the standard bitrate for DVD movie that you buy at the store?

Doubtfull you will see a difference between 6000 and 10000 if you are using footage from a consumer device. Most Retail DVDs tend to use an average between 4000-just under 6000. Carefull going above 8000kb/s, some DVD players could have issues decoding that high of a bitrage coming from a DVD R(W) disc.


Depending on the footage is what will make VBR vs. CBR better or worse. If you have mainly still pictures with slow pans and little to no action, CBR can yield the better quality.

If your footage contains both no action, and high action, VBR is better. This allows high bitrate to be allocated to the action scenes and using lower bitrate for the stale scenes. VBR is most effective when space is a priority.

Since you seem to have more than enough space, see which looks better to your eyes. CBR should be more than adequate in your situation.

VBR and CBR at the same average bitrate will yield the exact same file size. The encoder is going to maintain an average you set. CBR at 5000 will give you about 2hours on a DVD, same as VBR with an average of 5000.

A downfall to VBR, is that the worse case scene will always look worse when compared to CBR. With VBR, that scene is given a lower than average bitrate to preserve bitrate for the action scenes. Likewise, the heaviest action scene will look better with VBR when compared to CBR, because with a VBR encode, those scenes are given higher than the average bitrate.

VBR can be considered to be constant quality. The encoder attempts maintain the same quality across all scenes. CBR can be considered to be variable quality.

[ZippyP.]

I think disturbed1 pretty much covered it. If you want to go below 5,000 then you would probably see a difference with VBR. If not, then don't bother with it.

Also, what resolution are you using for your DVD? Since you're converting from home footage, 352x480/576 (1/2 DVD) should be fine.

[DivXExpert]

Here is the deal, they are the same quality for the bitrate. But VBR does not use bitrate it does not need, so it can use more bitrate for the parts that need it. So VBR saves space, but it uses that space it saves on parts that need more. So the end quality is higher on VBR.

[thor300]

I find its a noticeable difference for DV footage encoded at CBR 6000 compared to VBR with avg 6000, max 9000. If i have to convert DV to DVD really fast i use CBR 8000, as 6000 will give artifacting on pans.

[DVD_Ripper]

Also, what resolution are you using for your DVD? Since you're converting from home footage, 352x480/576 (1/2 DVD) should be fine.

If you are encoding at 1/2D1 then your encoding rate can be decrease as the resolution is 'cut in half'

I've been happy (little artifacts) when capturing at 1/2D1 at 4000VBR (in essence close to 7-8k "rate" for full DVD capture).... and I've read that 3kVBR 1/2D1 provides decent results.

Let us know how you make out.

[vcdhelppos]

I am using the DVD NTSC setting. it shows MPEG-2 video, 720x480, 29.97 fps, CBR at 8000 bitrate.

Now, re-encoding my 31 mins AVI at 8000 bitrate. size is now 1.8GB. time to encode shows about 48 mins. so for a 4.3GB DVD-R, I can fit about 1 hour and 15 mins of video.