XDCAM HD: VBV bufsize parameter

[m.hub...@gmail.com]

Hi all

I have a question about the "VBV bufsize"-parameter :

-In "ffmbc.c" in opt_target() one can find the following lines for the
"XDCAM HD422"-target:
opt_default("bufsize", "17825792");
opt_default("rc_init_occupancy", "17825792");


-On http://www.itbroadcastanddigitalcinema.com/ffmpeg_howto.html
there's another XDCAM-example:

ffmpeg -i <input_file> -pix_fmt yuv422p -vcodec mpeg2video -flags
+ildct+ilme -top 1 -dc 10 -flags2 +ivlc+non_linear_q -qmin 1 -lmin
'1*QP2LAMBDA' -vtag xd5c -rc_max_vbv_use 1 -rc_min_vbv_use 1 -b 50000k
-minrate 50000k -maxrate 50000k -bufsize 36408333 -bf 2 -aspect 16:9 -
acodec pcm_s16be -f mov output.mov -newaudio

My questions are:
1.) Which of the two "bufsize" values is "correct"... and WHY?
2.) Is there a "formula" or a "rule of thumb" that has been used to
set the param in ffmbc?

3.) Does anybody know about a good text/description about the "VBV
buffer size"-parameter for MPEG2.

4.) In ISO/IEC 13818-2 all "vbv buffer size"-MAXIMUM values seem to be
smaller than the ones used in the examples above.

Thanks for your help.

Regards,
Michael

[Baptiste Coudurier]

Hi,

On 10/9/11 7:42 AM, m.hub...@gmail.com wrote:
> Hi all
>
> I have a question about the "VBV bufsize"-parameter :
>
> -In "ffmbc.c" in opt_target() one can find the following lines for the
> "XDCAM HD422"-target:
> opt_default("bufsize", "17825792");
> opt_default("rc_init_occupancy", "17825792");
>
>
> -On http://www.itbroadcastanddigitalcinema.com/ffmpeg_howto.html
> there's another XDCAM-example:
>
> ffmpeg -i<input_file> -pix_fmt yuv422p -vcodec mpeg2video -flags
> +ildct+ilme -top 1 -dc 10 -flags2 +ivlc+non_linear_q -qmin 1 -lmin
> '1*QP2LAMBDA' -vtag xd5c -rc_max_vbv_use 1 -rc_min_vbv_use 1 -b 50000k
> -minrate 50000k -maxrate 50000k -bufsize 36408333 -bf 2 -aspect 16:9 -
> acodec pcm_s16be -f mov output.mov -newaudio
>
> My questions are:
> 1.) Which of the two "bufsize" values is "correct"... and WHY?

Any buffer size that is within the specs is correct.
I wrote the one on that blog.
The XDCAM specs itself specify a smaller bufsize because of the memory
requirement that would impose on equipment.
FFmbc uses the one written in the specs.

If you don't specify any bufsize, ffmbc will compute the maximum possible.

> 2.) Is there a "formula" or a "rule of thumb" that has been used to
> set the param in ffmbc?

The values used by FFmbc are from the specs.

> 3.) Does anybody know about a good text/description about the "VBV
> buffer size"-parameter for MPEG2.

See ISO 13818-2.

> 4.) In ISO/IEC 13818-2 all "vbv buffer size"-MAXIMUM values seem to be
> smaller than the ones used in the examples above.

Huh ? The maximum buffer size in 422P@High is 47185920 (~47mbits)

--
Baptiste COUDURIER
Key fingerprint 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
FFmpeg maintainer http://www.ffmpeg.org

[m.hub...@gmail.com]

Hi Baptiste

Thanks for your reply.

1.) SORRY about my wrong statement about 13818-2.
It seems that I have to organize the latest revision of the spec.

2.) You said: "The XDCAM specs itself... "
Where can I download/buy the spec-document (from Sony?) that contains
the vbv - information?

Many thanks for ffmbc.. !

Best regards,
Michael






On Oct 9, 9:53 pm, Baptiste Coudurier <baptiste.coudur...@gmail.com>
wrote:
> Hi,

>
> On 10/9/11 7:42 AM, m.huber....@gmail.com wrote:
>
>
>
>
>
>
>
>
>
> > Hi all
>
> > I have a question about the "VBV bufsize"-parameter :
>
> > -In "ffmbc.c" in opt_target() one can find the following lines for the
> > "XDCAM HD422"-target:
> >          opt_default("bufsize", "17825792");
> >          opt_default("rc_init_occupancy", "17825792");
>

> > -Onhttp://www.itbroadcastanddigitalcinema.com/ffmpeg_howto.html