[vorbis] Multiple tracks per file, or continuous audio support

[Michael Smith]

>This doesn't work with MP3s.  MP3s use frames in the
>frequency domain with overlapping time spans...the
>result being that at least a half-frame of silence is
>appended to the end of a track.  So you have a choice:
>record the spanning tracks separately and hear a
>distracting "pop" as the player switches between them,
>or encode all the continous tracks together and
>discard their identities, with the side effect of
>creating a potentially huge file.
>
>I saw a post on MP3.com (somewhere under the Rio Volt
>SP250 or that JVC thing) that said the Vorbis will
>conquer this problem.
>
>My question is:  how?  Vorbis records in the frequency
>domain too, right?

Vorbis has the same problem, BUT has a technique to deal with it correctly.
In the bitstream, there's sufficient information that the decoder knows
(this has worked since beta1, and even earlier) which bits to discard from
the start and end - the output is, as a result, exactly the same length (in
samples) as the original input.

>
>I want my cake and I want to eat it too.  I either
>want fully continuous-capable individual tracks with
>no discontinuities, or I want a way to mark a single
>large file with several embedded tracks, AND be able
>to navigate into them randomly, AND be able to split
>them into little files later in case I'm making a
>compilation.

Vorbis actually gives you BOTH of these - as I described above, the
individual tracks work fine. Also, vorbis lets you have multiple streams in
a single file, following each other - so you could have one file with a
seperate stream for each track, which gives you everything you wanted
(although player UI typically makes this hard to take full advantage of -
write your own player if that's a problem :-)

Michael

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