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

[Mike S]

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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