[FFmpeg-devel] [PATCH] AC3 decoder CRC check

Michael Niedermayer michaelni
Tue Sep 11 00:28:47 CEST 2007


On Mon, Sep 10, 2007 at 09:23:32PM +0200, Andreas ?man wrote:
> Hi
> Justin Ruggles wrote:
> > CRC checking aside, the AC-3 decoder can definitely be made better as 
> > far as error detection.  It will probably slow down decoding a bit 
> > though.  The AC-3 specification actually gives a list of error 
> > conditions that can be checked for.
> Did we reach any consensus whether or not adding an optional
> CRC-check would be a good idea?

IIRC the consensus was to add proper checks to detect bitstream
errors and do some error concealment on the damaged parts
if that doesnt work (=someone who knows AC3
explains with refering to the relevant papers or sections of the
ac3 spec why checking the crc and then doing error concealment is
better) then we surely could do that, but we dont need any flags
here its just do whats best and use the error_concealment / resilince
variables as appropriate

and note, papers explainging what is best come with PSNR or equivalent
values for the various tests they performed with damaged ac3 and various
different detection and concealment stratgies and they dont come in
form of a wikipedia page, .html faq or some "how to improve sound
quality on my broken binary ac3 decoder" discussion on some forum


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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