[FFmpeg-user] Probing jpg, png and tiff images without decoding frames

[Nicolas George]

Le decadi 20 thermidor, an CCXXI, Paul B Mahol a écrit :
> Yes, it is currently not possible, but I guess one could hack something
> which will just add some private option to interested decoder(s) to just fetch
> headers - without actual uncompressing of frames.

That is an interesting idea. It does not even need to be a private option,
since it makes sense for a lot of codecs, and would be of use for lavf too.

If the feature is implemented in the codec, it just returns immediately when
it has the format properties, before allocating a frame. If it is not
implemented, the frame is decoded and then discarded, that wastes time just
as it does now.

In fact, I half expected AVDISCARD_ALL to have this effect. It seems it does
not, or I did not test properly.

Regards,

-- 
  Nicolas George
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