[FFmpeg-devel] [PATCH] tools/target_dec_fuzzer: Limit error concealment to max_pixels

Michael Niedermayer michael at niedermayer.cc
Mon Nov 20 21:33:09 EET 2017

On Mon, Nov 20, 2017 at 06:30:28PM +0000, Kieran Kunhya wrote:
> >
> > On Mon, 20 Nov 2017 at 17:26 Michael Niedermayer <michael at niedermayer.cc>
> > wrote:
> > Error concealment is time consuming, limiting it in a pixel dependant way
> > allows
> > the decoder to be fuzzed with more frames quicker
> >
> How is this a reasonable fix considering you have submitted numerous
> patches to fix "long-running" loops?

Iam not sure i understand, i think we misundestand each other here

the fuzzer tests many random pieces of data, and if on average one
takes 10 secs it tests half as many as if one takes 5sec on average

So making te fuzzer spend less time on the most timeconsuming part
of the code means more fuzzing per same cpu time.

Or said differently if decoding takes an average of lets say 10 ms
per frame and error concealment of a frame takes 100ms on average
if we cut down the amount of cases that do concealment we increase
the number of frames we can fuzz by more than we reduce the number of
error concealment cases.
At least that is the idea

> Surely it's a bug that people can craft streams that cause error resilience
> to lock up the machine.

yes, absolutely

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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