[FFmpeg-devel] Float vs. fixed-point audio codecs

Vitor Sessak vitor1001
Fri May 14 17:28:42 CEST 2010

M?ns Rullg?rd wrote:
> With the addition of Michael's floating-point MPEG audio decoder this
> week, we have, for the first time, both float and fixed-point
> implementations of a codec.  Having both is a good thing, since which
> one is faster depends on the CPU.  This presents us with several new
> problems to solve and decisions to make.
> Please add your thoughts on this, particularly if there's something
> important I've overlooked.  If we can agree on an approach, I'll try
> to put some patches together as soon as possible.
> Choice of codec
> ---------------
> With two implementations available, we must provide a good way of
> choosing which one to use.


I don't have much opinion about this, my only suggestion is to not have 
two redundant decoders compiled when configured with --enable-small .

> Testing
> -------
> Regression tests currently depend on decoder output being bitexact
> across all supported targets.  Unfortunately, this is not the case for
> the floating point MP3 decoder, so until a scheme is devised allowing
> testing of inexact decoders, we will have no choice but to test only
> the fixed-point version.  This of course means it will have to be
> enabled for testing to be possible.

For "make test", testing if stddev between fixed-point and float is 
really small should at least avoid major breakages. For FATE, I'm still 
waiting Mike's 1-off method [1]...


[1] http://multimedia.cx/eggs/revised-fate-test-types/

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