Quantizer per frame?

[a uio]

Just an informational question...

In Mpeg video encoding, does each frame get its own quantizer, or does each block inside a frame get its own quantizer? Or perhaps something else?

Cheers,
A

[foxyshadis]

Per-frame is the most common. Per-block is generally not default, but it's known as adaptive quantization, or psychovisual enhancement, in a lot of codecs. (Although nero/ateme's psycho includes certain other minor effects.) I believe when a macroblock matches the frame's default quantizer it can skip coding it, and same when the frame matches the entire clip's default quant.