max bitrate & HRD

[ranchu]

Hello,

I would like to ask if max bitrate is determined according to hrd buffersize, i.e. what is the connection between these 2 parameters in encoder.

Best regards,
Ran

[sneaker_ger]

The maxrate is the maximum bitrate with which the buffer will be filled. (leaky bucket model/vbv)

[ranchu]

when using VBR, it change the bitrate above and below the target bit rate. Is hrd buffer size equal to max bitrate allowed in VBR rate control ?
Regards, Ran

[sneaker_ger]

?
a buffer is a buffer, it can hold a number of bits
a rate is a rate, it means a number of bits per time unit
They are not the same.

[ranchu]

Hi Sneager,

In VBR, bitrate changes around average bit rate. In some of the VBR algorithm we can determine the maximum bit rate. I am trying to understand if this max bitrate is related or determined according to buffer size, or if it is totally different parameter/concept.

Regards,
Ran

[Asmodian]

The true instantaneous max-bitrate observed in the file does depend on buffer size to some degree, it is a quite complex relationship when thinking about it from the outside though.

With the buffer full VBV could theoretically let you empty it all for one frame, as long as the next frame could be covered by its share of --vbv-maxrate. This would probably never happen in a real file though.