Constant Quality & HT profile

[o770]

How do I predict the lowest Quantizer value to achieve constant quality and remain under the HT profile?
The goal is constant quality and Certified Devices playback.
Thanks!

[DigitAl56K]

Mark in a representative sample of the source video and encode it in target quantizer mode with the feedback window enabled. Set the graph to show the frame quantizer and then slowly adjust the quantizer using the sliders at the bottom of the feedback window until you reach the point where lowering it any further tends to cause fluctuations in the typical frame quantizer. Note that the frame quantizer for I/P and B frames is different - this is normal. Also, if you use non-integer target quantizers then in effect you're setting a target mean for the quantizer distribtuion of I/P frames, i.e. if you set target quant = 4.5 it would be normal to see I/P frames at both Q4 and Q5.

It's unlikely you'll get constant quantizer over the course of a length clip unless you use higher quantizers, so in my opinion this excersise is impractical and also unnecessary - perceptual coding is not about lossless compression in any case. Does it matter if the quantizer is raised slightly for a handful of frames throughout the movie? Would you notice when you're watching it at 24fps?

What I do find useful is encoding short representative samples with the feedback window on in order to choose the target quantizer and estimate bitrate.

Remember that the encoded frame displayed in the feedback window has no post-processing (deblocking, deringing).

Hope that helps!