[vorbis] Average Bitrate Calculation

Michael Smith msmith at labyrinth.net.au
Tue Oct 2 03:40:09 PDT 2001

>I'm certainly no expert on audio formats but it seems that they all
>suffer from lack of basic information at the start of the file.  It is very
>inefficient to be jumping around thousands of files to obtain the length
>(duration) of a playlist when the length of a song could simply be placed
>at the beginning of the file after encoding.  Similarly with an average 
>bitrate.  Only the Xing header for MP3 comes to mind as being efficient.

Ogg (and vorbis) are designed to make streaming sensible and possible.
Information about things like length simply isn't possible at the start of
the file in the sense that you mean. Since it's pretty simple to find the
length of the stream anyway it's not that big a deal. 

>On a similar subject, is there an easy way of determining the number of bits
>per second of the original PCM source.

You know the number of samples per second (vorbis_info->rate), but you don't
know the sample size in the original, since the concept is irrelevent to the
way vorbis works. There IS no 'sample size' in vorbis.


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