[FFmpeg-devel] Behaviour of liba52 decoder

Baptiste Coudurier baptiste.coudurier
Fri Jan 11 10:59:39 CET 2008

Hi Justin,

Justin Ruggles wrote:
> Michael Niedermayer wrote:
>> On Thu, Jan 10, 2008 at 06:54:13PM +0000, M?ns Rullg?rd wrote:
>>>>> On Thu, Jan 10, 2008 at 06:28:52PM +0000, M?ns Rullg?rd wrote:
>>>>>> I'm surprised nobody has mentioned the fact that we now have a native
>>>>>> AC3 decoder, so there is no longer any need for the liba52 wrapper.
>>>>>> Is there some reason I'm missing why it's still there?
>>>>> Good question. I'd be happy to see it removed.
>>>> if ours is faster sure remove liba52 support ...
>>> Is speed the only deciding factor here?  I suppose I could benchmark
>>> decoding a DVD or two.
>> The question is probably if we have volunteers to do more complete testing
>> that is
>> * .o size
> object sizes (--strip-debug):
> aac_ac3_parser.o     1136
> ac3dec.o            15784
> ac3.o                4688
> ac3_parser.o         2164
> ac3tab.o             2873
> fft.o                2872
> mdct.o               2348
> -------------------------
>                     31865
> for apples-to-apples:
> ar rc ffac3.a {files above}.o  33170
> /usr/lib/liba52.a              42914
> It will grow with the addition of E-AC3, but also keep in mind that 6/7
> of those files are shared with other codecs.
>> * memory requirement
> I'm not really sure about the best way to test memory
> requirements...valgrind?
>> * quality (are there specific tests mandated by the ac3 spec?)
> Sadly, no.  The only tests I know of come from Dolby, and they only give
> them out to companies who apply to license "Dolby Digital Technology"
> for commercial use.  I would love to get my hands on a conformance test,
> but after searching around it seems unlikely.  The closest I could find
> is a list of the contents of the CD's Dolby gives out for the licensing
> process, and all the testing samples and documents are flagged as
> confidential information.
>> * feature completeness (i assume we are better especially with EAC3 around
>>   the corner and liba52 being not very actively developed lately AFAIK)
> Yeah, features are pretty much complete for AC3 except for some of the
> metadata and more complete downmixing (needs LtRt and everything else
> except mono and stereo).  So yeah, 99% feature complete.  And same as
> liba52 decoder as-is.
>> * error concealment (being mandatory for EAC3 we should be as good or better
>>   here as well eventually)
> I'll go ahead and work on error concealment on the E-AC3 side of things,
> and if everything works okay I can add it to AC3 even if E-AC3 isn't
> quite ready for inclusion into FFmpeg SVN. (on that note, I do think
> it's getting pretty close)
>> Anyway speed tests alone would already be very interresting
>> C and SSE of course for both
> I'm quite surprised with Mans' speed test results and will try to
> duplicate them.  A few months back ffac3 was slower for me than liba52
> for 5.1 decoding, but slightly faster for stereo.

Btw, what's still left to change license to LGPL ?

Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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