[FFmpeg-devel] [PATCH]lavf/swfdec: Reduce score when auto-detecting swf files

[Carl Eugen Hoyos]

2018-01-19 18:33 GMT+01:00 Michael Niedermayer <michael at niedermayer.cc>:
> On Fri, Jan 19, 2018 at 04:21:54PM +0100, Tomas Härdin wrote:
>> On 2018-01-18 21:28, Carl Eugen Hoyos wrote:
>> >Hi!
>> >
>> >The probe score for swf files (with uncompressed headers) is currently
>> >very high after testing a little more than 24bit, attached patch
>> >reduces the score.
>> >
>> >Please comment, Carl Eugen
>>
>> Would be consistent with the discussion about .c2 files. Could we document
>> this in avformat.h? Something like:
>>
>
>>     // Score should be no more than AVPROBE_SCORE_MAX * identifying_bits/64
>>     // if the number of identifying "magic" bits are less than 64
>
> this is a bit oversimplifying it i think

I don't disagree.

> its more a question of "entropy" than bits
> 24bits tested for at one location is much stronger than 24 bits found at any
> location in 20mb. (later is in fact close to telling us nothing)

Of course.

I believe that for ~64 initial bits, we should return MAX - 1.

But for many formats, "initial bits" is of no relevance.

Carl Eugen