[x264-devel] Re: Multipass encoding with CBR

[Loren Merritt]

On Tue, 21 Feb 2006, Måns Rullgård wrote:
> "Patrick Lefevre" <pat at wischip.com> writes:
>
>> In the DVD<->Mpeg-2 days, we were forced to do MB level BRC,
>> otherwise with frame level quantization it's hard to raise the BR
>> without under-flowing the vbv_buffer (from quite to super-busy
>> scenes).
>> Do the experts agree? Will this be a consideration in x264 as well?
>
> There used to be MB-level RC in x264, but it didn't work very well and
> was removed.  Loren should be able to elaborate on this.

The original MB-level RC reacted way too strongly to varying complexity, 
thus introducing more QP variation than was needed. And still didn't 
always prevent buffer underflows. I replaced it because a constant QP per 
frame with underestimated bitrate constraints gave better quality for 
similar vbv strictness.
Expect to see a better version of MB RC Real Soon Now (tm).

--Loren Merritt