[vorbis-dev] Re: Re: Re: "wrong" total time from ov_time_total

[Rodrigo Gómez]

Thanks for the explanation!

At the end, this can change the lenght of the audio? If the packets are
overlapped, then it will be logical to think that the audio will be a little
bit less, isn't? Or are the packets "larger" than the original, to contain
the overlapped sections? In either case, I guess that the ov_time_total and
so on already take this in consideration, no?

Using a better quality will have less overlaping? I have tryed with this,
and IIRC, it didn't helped. But I don't have the numbers here.

Thanks!

Rodrigo Gómez

"Mike S" <wickedchicken at plasticpenguins.com> escribió en el mensaje
news:3F666013.2010302 at plasticpenguins.com...
Rodrigo Gómez wrote:

<p>>
> I don't understand that vorbis packets overlap. What is that? Or how would
I
> deal with it?

Vorbis uses the modified discrete cosine algorithm to encode audio. One
of the reasons for using this is that the eventual representation in
each packet is scaled down at each end. If the packets were simply
concatenated without this scaling, every time audio spanned a packet
boundary there would be a jump from one packet to another. This will be
audible, and add to the intrablock noise. This can most easily be
demonstrated by watching an MPEG video or JPEG picture at a low bitrate
- the blocks (8x8 squares in those cases) will be very noticable. By
scaling down the edges of the packet, and then overlapping the scaled
edges with the next packet, a smooth transition can be achieved. I
forget where but there is a document about Vorbis explaining this with
diagrams and curves.


-- 

~Mike
wickedchicken at plasticpenguins.com

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