[vorbis] Slow stream opening (Was Re: Average Bitrate Calculation)

Monty xiphmont at xiph.org
Wed Oct 3 08:28:25 PDT 2001

On Wed, Oct 03, 2001 at 08:57:58AM -0000, Alen Ladavac wrote:
> > >  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.
> >
> > On average, Ogg seeks three-four times at open.
> While we're at it... On my testcase, it proved that opening an ogg stream
> using vorbisfile takes significantly (and I mean _really_ noticeably
> significantly) longer than opening an mp3 stream using amp11lib. It turns
> out that the problem is in the stream's seekability. If I don't provide the
> seeking callback, the thing works like a charm.

Vorbisfile will not try to parse stream structure in a non-seekable
stream.  Doing things this way is perfectly valid, and a good trick.
You just won't know total stream length or average bitrate.
Everything will still work.

> I guess it is impossible to fix that for a VBR stream, right?
> (It's not like I need seeking anyway, but maybe someone will.)

All streams are VBR, even when they aren't :-) Ogg/Vorbis is never
CBR, even if an encoder mostly fakes it.  Vorbisfile is slower at a
full open than a non-seekable open, but it shouldn't be absurd...
Could you send me the file presenting all the trouble?


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