peak bit rate for net

zoobie · Post by **zoobie** » Wed Jan 16, 2008 8:54 pm

Rather than hit or miss...I'll just ask

I'm making small wmv clips for the net using VBR 422kbps with a peak rate of 634kbps (48kbps for audio). This is 12.9mb total.

Now, if I reduce the peak bit rate to 630kbps keeping everything the same as above, the file size is now 13.1mb total.

What is the relationship between the video bitrate and the peak bitrate?

It's coming out beautiful, clearer, and 25-40% smaller using VBR vs CBR, btw.

Thx

troppo · Post by **troppo** » Thu Jan 17, 2008 1:15 am

the peak bit rate is as high as it will go. The encoder attempts to average it out at the bit rate you set, but goes up to the peak rate for scenes with alot of movement and colour.

zoobie · Post by **zoobie** » Thu Jan 17, 2008 9:20 am

and transitions

but there's also a some sort of formula being used...
suddenly, the images are much clearer by actually limiting the peak to 630kbps in the above case
I've gone all the way to 2000kbps peak and it was blurring

troppo · Post by **troppo** » Fri Jan 18, 2008 8:58 am

perhaps the higher the peak rate is, the lower the actual rate has to be in order to keep the average rate at whatever you set. For instance, if the peak rate is 2000 and it hits it a couple of times in the encoding, the rest of the file has to be much lower than the nominal rate in order for the average to come out around where you set.