[vorbis-dev] Length of song calculation

[Ross Levis]

Thanks Michael I'll have a go.  Sounds like a little less work & more efficient
than MP3's with ID3v2 tags.

Cheers,
Ross.

Michael Smith wrote:

> At 05:40 PM 7/23/01 +1200, you wrote:
> >Hello Developers
> >
> >I'm writing a playlist creator app for radio stations (in Delphi) which
> >supports WAV & MP3 files & I would like to add OGG support.  All I need is
> >the ability to read the length of the track from the file header.  The
> >documentation on the website is beyond me.  I would rather not include a
> >bulky library that does everything else.  Does anyone have any Delphi code
> >or can point in the right direction?
>
> As with mp3, the length of the track isn't available just from the start of
> the file. Examining the header is insufficient.
>
> If you don't want to use libvorbis/libvorbisfile, then this isn't trivial,
> but it isn't that hard (though it gets moderately complex when you add
> chaining support.). However, it's made much easier if you use libogg (this
> is a very small library, not a bulky one).
>
> Basically, you want to find the final page of each logical stream. For the
> simple case of a non-chained stream, this just means finding the final page
> in the file, which is pretty simple. From that, get the 'granulepos' value.
> That's the number of samples in the stream. You can then get the length by
> dividing by the sample rate. Sample rate is given in the primary header
> (the first packet) - libvorbis does this, but it's easy to find without
> libvorbis. It's at offset 12 in the first packet, 4 bytes (little endian)
> giving the sample rate. See vorbis/lib/info.c, around line 193, for the
> code which reads this in libvorbis.
>
> Michael
>
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