[vorbis-dev] ogg multithread encoding

[Rob D]

I dont see the benefit of a multi-threaded encoder on a single CPU. The CPU
usage would actually be worse than a single threaded app when you have
several threads fighting for access to different pieces of the same source
files and wouldnt be any faster.

On the other hand, coordinating several CPUs to decode a single file would
help, as the extra overhead of the encoders figthing over the disk for
source and output files would be offset by the extra available CPU power.

Unless all the CPUs are of comparative speed, some threads will finish
first, and have to wait, wasting CPU time.

I converted over 20000 mp3s into oggs, and with 14 computers at home, it is
much easier (and faster), to have the different speed computers just encode
separate files. It took less than a week.

Rob D

-----Original Message-----
From: owner-vorbis-dev at xiph.org [mailto:owner-vorbis-dev at xiph.org]On Behalf
Of Michael Smith
Sent: Wednesday, June 18, 2003 5:55 PM
To: vorbis-dev at xiph.org
Subject: Re: [vorbis-dev] ogg multithread encoding

<p>On Thursday 19 June 2003 01:28, torque wrote:
> >Ehm, simply concatenate them together? Ofcourse you have some
> >overhead with the headers being repeated, but it will yield a valid
> >Ogg file...
>
> OK, it works:) Actually, it seems to be a vaild .ogg file. But what about
> those headers? In XMMS, Winamp etc. the time is not properly displayed. I
> think, that maybe I could leave only the first header (but I don't know
> exactly how many bytes is it) and update certain values in it somehow.
What
> do you think about it?

You _could_ do this, but it's difficult. There are quite a few special cases
you'd need to get right. You should read the spec (ogg spec, and the
relevant
bits on embedding into ogg and the headers of the vorbis spec) if you want
to
do this.

You could also come to the realisation (as have other people who have looked
into doing this) that a parallel vorbis encoder really isn't that useful,
given the encoder speed relative to current (or even somewhat old) cpu
speeds.

Mike

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