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

[Reimar Döffinger]

Hello,
On Sun, Sep 02, 2007 at 06:32:26PM +0100, M?ns Rullg?rd wrote:
> Andreas ?man <andreas at olebyn.nu> writes:
> > M?ns Rullg?rd wrote:
> >>
> >> I reckon the decoder will notice if the frame is damaged anyway, and
> >> see no reason to explicitly check the CRC.
> >
> > I must say i disagree here.
> >
> > I've uploaded a sample to incoming/ac3-seriously-damaged recorded
> > from a DVB broadcast. The recording has deliberately poisoned with
> > transport stream packet drops to make the issue more clear.
> > Normally you would not have this rate of errors of course.
> > But remember that DVB specifies that one error per hour is acceptable,
> > and having these type of clicks every now and than makes listening
> > to TV an unpleasant experience.
> >
> > Anyway, one can notice that all the clicks and blipps goes
> > away completely with the CRC check.
> 
> In that case I say the AC3 decoder needs to be improved to reject
> these damaged frames.

Especially since the CRC thing assumes the best solution to even a single
flipped bit (possibly even in the CRC itself!) is to just drop the whole
thing (at least unless someone implements something better in lav*).
Though, actually if there is a way to _disable_ error resilience it
might make sense to enable this check in that case...

Greetings,
Reimar D?ffinger