Re: variable bit rate decoding?

On Thu, 2003-11-27 at 09:59, Mandar Mitra wrote:
> Can XMMS play variable bit-rate encoded mp3 files?
> 
> When I play certain mp3 files using xmms, the duration
> displayed in the playlist keeps fluctuating, sometimes
> quite drastically. Could this be because the file is
> encoded using VBR?

xmms can play them, although the behavior will be a bit erratic (as
you've seen) unless the mp3s have a header written at the start in the
style the Xing mp3 encoder writes (LAME also writes these headers.)  The
Xing header contains the number of mp3 frames, the total file size, and
a table of seek points (so that an approximate point within the mp3 file
can be found without searching through the whole thing.)

When the Xing header is not present, xmms will estimate the song length
based on the file size and the size the current frame (which will vary,
sometimes drastically, in a VBR mp3.)  This is the behavior you're
describing.  A little experimentation with Xine shows that it seems to
have some trouble as well, but it looks as though it's trying to smooth
out the transitions a bit (possibly using the average bitrate from the
last X seconds.)

Hope that provides some insight,
-- 
Ben Winslow <[email protected]>

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