[mpeg2] Re: question about the mpex and vbv buffer and vbv delay

[Luca Abeni <labeni@mbigroup.it>]

Hi Samuel,

> > Finally, I am (obviously) encoding CBR video, but a TS analyzer that I
> > am using shows that the video bit rate is not that constant (it is
> > almost constant, but there are periodic spikes). Maybe this can be the
> > cause of the problem that I am seeing? If yes, does anyone know how to
> > obtain a "more constant" bitrate (maybe some of the encoding parameters
> > are not set in an optimal way for CBR encoding)?
> 
>   Do you know how does your tool analyse the bit rate?
I don't know: I did not write that program, and it is a closed-source :(

> I wrote a little
> program which simply looks for the PCRs and works the bit rate out
> dividing the amount of bytes between each pair of consecutive PCRs by
> the subtraction of those PCRs and it yields exactly 6000000 bits/seg
> for all pairs of PCRs.
I did something similar in the past, to verify that the TS bitrate is
constant (and in fact, it is ;-). But I did not look at the video
bitrate (I am just trusting the TS analyzer)... I'll try to have a look.

>   I have other tool that says there is a small PCR jitter, but I don't
> have the source and I have no idea about why is it saying that :(
I suspect it is referring to the fact that the difference between two
consecutive PCR values is not constant, but oscillates between 40.35ms
and 41.36ms. Anyway, the PCR does not have to be periodic, hence this is
not a problem (I think).

				Thanks,
					Luca
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