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

[Robert Krüger]

On Wed, Aug 7, 2013 at 4:15 PM, Nicolas George
<nicolas.george at normalesup.org> wrote:
> 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.
>
global codec option sounds great. I don't know if that could also then
be used to be able to extract information like frame type without
actually decoding frames which would be super-useful but that is of
course beyond the scope of the original request.