[vorbis-dev] ogg multithread encoding

[Santosh Chandwani]

I am new to Vorbis and not very familiar with its encoder yet. However,
based on my previous experience with other codecs including MP3 and
MPEG-4, there are two ways you can resolve this problem.

The first method would be suitable for a workstation environment where
you don't have to manage the system resources and have a mature kernel
with multi-threading and sync support. The input data (in this case the
wav file) should not be split into separate wav files with different
headers as you have done. You create a master thread which manages the
encoding and this has the responsibility to read the wav header and
manage the encoding parameters. The master thread parses the wav file
and feeds chunks of it to each of the other threads. The chunk size
should ideally equal the number of samples in a Vorbis frame or the size
of the analysis window. Each of the slave threads then encodes the input
frame data and returns the output data to the master thread. This of
course requires that you have a separate API for encoding just a single
frame. Given that this is an open-source venture you can just extract
the functionality you want from the main encode loop to create a
suitable API.

If you are doing this for an embedded platform with multiple processors
where you have to manage the memory and code layout, etc, it makes sense
to split a codec functionally and have each thread or processor do a
part of the encoding and hand-off to the next thread in the chain for
processing.

Santosh

<p>-----Original Message-----
From: Michael Smith [mailto:msmith at xiph.org] 
Sent: Thursday, June 19, 2003 5:25 AM
To: vorbis-dev at xiph.org
Subject: Re: [vorbis-dev] ogg multithread encoding

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

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to
'vorbis-dev-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is
needed.
Unsubscribe messages sent to the list will be ignored/filtered.
--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-dev-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.