CBR variable quality?

[Premjit V.P.]

Hello guys!

I just wanted to know whether encoding in CBR gives variable quality. I understand that high action scenes require more bandwidth and quality gets reduced (and so it can be ignored for this question). I just wanted to know whether low action scenes wastes the excess bitrate for maintaining constant quality or uses all the available bitrate for giving out the maximum quality.

Thanks, Bye and have a happy celebration.

[bugster]

A particular scene will need a specific bitrate in order to achieve any particular 'quality' when encoded using an mpeg encoder. If you use CBR at a level higher than is needed, the encoder will pad the video stream to maintain the requested bitrate. This is wasted bitrate.

[monzie]

A particular scene will need a specific bitrate in order to achieve any particular 'quality' when encoded using an mpeg encoder. If you use CBR at a level higher than is needed, the encoder will pad the video stream to maintain the requested bitrate. This is wasted bitrate.

That is true, but by the same reasoning setting a midrange ave (say 4500) with a vey low min and a very high max is EVEN worse......ie what are you achieving.....do you know? If you want to go vbr then these settings are a good guide....1500min, 4500 ave and 6000max....note their is little point EVER going above 6000max.

Dont mix up (a common mistake) Hi MOTION with Hi ACTION (they are NOT the same!!!!!)...ones about camera movement (motion....does the camera ITSELF move or shake) and ones about the captured focal point(action)...action takes far less bitrate to encode than MOTION (most commercial movies have ACTION and not (camera) MOTION..as the cameras are on dollies/tracks and are not free hand so devoid of fast MOTION).

[bugster]

note their is little point EVER going above 6000max.

Everything you say is a valid contribution to the discussion with one exception, and that is quoted above. Where on earth did you get that idea from. Why does the DVD-video spec allow a max video bitrate of 9800 if it is not needed. How much bitrate is need to encode a 'low motion' scene (using your definition) where there are lots of flsahing lights such as a nightclub scene or rock concert. I think you need to revise your figures a little in those circumstances.

[rhegedus]

This post explains optimal CBR/VBR bitrates quite well:

CBR or VBR for MPEG2 master backups?

So for Full D1 8000 kbps CB will give us the maximum quality possible and about 6500kbps will put us to the middle of Good range, which is still fine.