On Tue, Mar 21, 2017 at 10:03:48AM -0300, James Almer wrote:
> On 3/21/2017 9:52 AM, Michael Niedermayer wrote:
> > On Mon, Mar 20, 2017 at 11:03:23PM -0300, James Almer wrote:
> >> Should fix ticket #6252
> >>
> >> Signed-off-by: James Almer <jamr...@gmail.com>
> >> ---
> >> libavformat/apngdec.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/libavformat/apngdec.c b/libavformat/apngdec.c
> >> index 7a284e32c2..75dcf74a0c 100644
> >> --- a/libavformat/apngdec.c
> >> +++ b/libavformat/apngdec.c
> >> @@ -421,7 +421,7 @@ static const AVOption options[] = {
> >> { "ignore_loop", "ignore loop setting" ,
> >> offsetof(APNGDemuxContext, ignore_loop),
> >> AV_OPT_TYPE_BOOL, { .i64 = 1 } , 0, 1 ,
> >> AV_OPT_FLAG_DECODING_PARAM },
> >> { "max_fps" , "maximum framerate (0 is no limit)" ,
> >> offsetof(APNGDemuxContext, max_fps),
> >> - AV_OPT_TYPE_INT, { .i64 = DEFAULT_APNG_FPS }, 0, INT_MAX,
> >> AV_OPT_FLAG_DECODING_PARAM },
> >> + AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX,
> >> AV_OPT_FLAG_DECODING_PARAM },
> >> { "default_fps", "default framerate (0 is as fast as possible)",
> >> offsetof(APNGDemuxContext, default_fps),
> >> AV_OPT_TYPE_INT, { .i64 = DEFAULT_APNG_FPS }, 0, INT_MAX,
> >> AV_OPT_FLAG_DECODING_PARAM },
> >> { NULL },
> >
> > why was there a max fps set ?
> > are there files which have huge and incorrect fps ?
>
> I have no idea. The author of the decoder may know. But apng is far from
> a widespread format seeing it has been supported by only one browser until
> like a week ago, so the chances of bad files like it could happen with
> jpg or png is most likely low.
>
> > if so this may cause a regression and just increasing the default value for
> > max_fps could be better.
>
> I guess 60 would be a saner max value than 15 as it is now, but i still
> wonder why would we have a max fps set as default to begin with.
> > IMO, if the worry was about a broken/incorrect headers (fuzzing or such), > then checking the CRC field for correctness may be a better idea than > crippling decoding of valid files by default. why do you think this could be related to fuzzing ? i dont know why the check is there but i had suspected that it was a workaround for broken encoders. Possibly not apng encoders but a more widespread format like animated gif that is transcoded to apng we have a similar max check in gifdec.c if gif files need it, gif files converted to apng should need it too and i would suspect that animated gifs are a major source for apng files, but maybe iam wrong [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Asymptotically faster algorithms should always be preferred if you have asymptotical amounts of data
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