[Flac-dev] Re: multiple core support

[Scot Thompson]

No, streams should stay.  Audio is NOT a file based process -- it's a
stream.  You can't listen to an entire song simultaneously.  You organize it
into files for later use, but you listen and record from a stream.
Stream-based storage is practically REQUIRED for an audio codec.  It's not
random access, it's sequential.  You can put wrappers around it to make it
convenient for file storage and conversions, but the codec itself must be
streams.
 
Multi-core support may not be practical for a variable-length encoding.  How
would you know where to write the next block when you don't know what size
the first block is going to be?  The functionality for that is not trivial
and is not currently implemented in the API.
 
Maybe somebody will write a multi-core file-based wrapper for you, or maybe
you could try writing one yourself.  Or if you disagree with Josh about the
direction of FLAC you can write your own codec.  But your nattering on and
on about how you think the API isn't right doesn't help at all and is very
annoying.

  _____  

From: flac-dev-bounces at xiph.org [mailto:flac-dev-bounces at xiph.org] On Behalf
Of Harry Sack
Sent: Saturday, September 08, 2007 6:06 AM
To: Brian Willoughby
Cc: flac-dev at xiph.org
Subject: Re: [Flac-dev] Re: multiple core support




2007/9/8, Brian Willoughby <brianw at sounds.wa.com>: 

Ralph,

The problem is that there is no clear advantage, at least in terms of
multiple cores, to the approach you're asking about.  In order to
allow each stage of the codec to overlap, you need smart buffering 
between each stage.  That adds code and complexity which isn't there
currently.  So you end up making the system do more work in the hopes
that there will be some overlap.  Basically, later stages get blocked 
waiting for their input buffer to fill, which means that you're not
really getting very much overlap at all, but plenty of multi-
threading overhead.  At least that's the predicted result - I admit
that nobody has tried this, to my knowledge. 



this is because of the limitations/design problem of FLAC API in particular.
When the developers had made a smart decision and based everything on file
based I/O you would get a HUGE performance boos when using multiple threads
divided between multiple cores, because they only thing to do was to split
the file output in different threads. 
But it's not clear to me why everything was based on streams...

Harry



Brian Willoughby
Sound Consulting


On Sep 7, 2007, at 18:25, Ralph Giles wrote:

On Fri, Sep 07, 2007 at 04:59:50PM -0700, Josh Coalson wrote:

> it actually is complicated.  the libFLAC api is not suited to a 
> multithreaded design because the i/o is stream-based, not file-
> based.  flac(.exe) is the file-based wrapper around libFLAC that
> allows it to work on files.  the way libFLAC buffers data is also
> impossible to parallelize without significantly changing the api.

It seems like buffering (especially compressed) blocks and writing them
to the stream in sequence wouldn't be a problem. Is there something in 
the way the blocking decisions are made that makes it hard to divide the
input audio this way?

  -r

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