[FFmpeg-devel] [PATCH 2/2] avformat/apng: set max_fps to no limit by default

[James Almer]

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 <jamrial at 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.

> 
> If no such files exist then this LGTM
> 
> wither way it needs a update to fate
> 
> [...]
> 
> 
> 
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