What is the bias settings in CCE

[baker]

I hjave been missing from the video scene for quite a while as my computer was broken and have seen that a lot of ppl are using this newly found bias setting in the ecl file.

Can somebody point out what this settings is and what it does please?

Also what is the default setting

Baker

[Lord_Asswipe]

That is my question too!
I know that if you decrease the bias, the q-factor goes up, so why does the DVD-9 to DVD-5 say: set the bias to 0?!

[Lord_Asswipe]

Nobody can help us out?

[baker]

if your doing dvd keep it up to 30

Baker

[jdobbs]

When you do your first pass the bit allocation per frame/gop is set based on a constant quality. The bias determines how much weight is given toward keeping that allocation. Setting it higher prevents wild swings in bit allocation between frames/gops. Setting it lower makes the encoder allocate more bits to high demand areas as needed and less to low demand.

My experience is that setting this to a low values (like "0") gives a higher quality picture when you are limited on size. I've heard there is a possiblity you could cause a variation that is too large for buffering... although it has never happened to me.

The higher you set this value, the closer you get to CBR rather than VBR.

[DVD__GR]

I tottally agree.Reading the cce pdf will explain to you detailed how bitrate is changing in graphs according to bias setting.YES 0 setting IS BEST..ALTHOUGHT i had slight problems in playback like mentioned when average bitrate goes about 2200 with min 0 and max 8500.SO i SET IT TO 5 and NO PROBLEMS!!

[Richard Iredale]

As the manual states, a Bias of 0 means most bits are allocated to complicated scenes, at the expense of simple scenes. A Bias of 100 means equal allocation, or effectively a CBR.

I experimented on a static (camera not moving) shot of river rapids. The shot begins with a slow fade-in from black. With Bias set to 0, the blue sky showed horrible shifting banding artifacts as the scene brightened. With Bias at 30 (the default), there was no banding visible.

Based on this, I'd have to say that a Bias of 30 is more artifact-free.

[jdobbs]

@Richard Ireland

Good point. I think the important thing to remember is to watch where the Q is positioned on the scale in the advanced settings dialog. In your case I would have to assume that setting the value to "0" would have caused the simpler scenes to rise above an acceptable level on the Q scale.

Since I use the Robshot method, I set the bias to "0" first and then set the bitrate to a point that brings the Q down below 10 (I usually aim for 5). If I don't have enough room with the bitrate I choose, then I'd have to get creative and decide whether I'd want to give more bandwidth to the simpler scenes (there are normally a lot more of those).

The reason I like setting it to "0" is that more often than not the Q spikes are associated with complex/high action scenes.

I think it all depends on the application.