[x264-devel] Re: [x264-devel]the size of vbv buffer

[Loren Merritt]

On Mon, 26 Mar 2007, jogging song wrote:

> In X264, I set a small value for vbv_bufsize and get a message "The VBV
> buffer size  to samll, and
> using xxx kbit". In the code, I find its default value is three times
> average frame size.
>   h->param.rc.i_vbv_buffer_size = 3 * h->param.rc.i_vbv_max_bitrate /
> rc->fps;
> can anyone suggest how to set the value for vbv_bufsize. I think the buffer
> at least should be able to cantain the
> biggest frame that the encoder generates.
>
> The default vaue for vbv_buffer_init is 0.9. When I set vbv_buffer_init to
> 0, I find that the first I frame
> gets a bigger QP than 0.9. In my opinion, when the vbv buffer contains less
> bits, Rate Control should give out
> a small QP to fill the buffer.
>
>  In Rate Control, vbv buffer is filled by
> rct->buffer_fill_final += rct->buffer_rate - bits;
>  The bits exceeding the average frame size will accumulate in the VBV
> buffer. In video coding, I find the value is
> near the size of vbv buffer. VBV buffer is the input buffer of decoders. In
> anytime of video decoding, bitstream for
> next frame should be feeded in input buffer, then decoders begin to decode
> the bitstream. If accumulating bits in vbv
> buffer is near its size, decoders can't put more bits in the input buffer.
> Am I right?

Either you don't understand VBV, or I don't understand you. Either way, I 
can't answer your questions.

--Loren Merritt

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