[FFmpeg-devel] Fwd: GSoC: APNG

Michael Niedermayer michaelni at gmx.at
Tue Mar 24 00:45:45 CET 2015

On Mon, Mar 23, 2015 at 11:02:21PM +0000, Donny Yang wrote:
> On 24 March 2015 at 01:18, Michael Niedermayer <michaelni at gmx.at> wrote:
> > Either way, changes to libavcodec and libavformat should be in 2
> > seperate patches
> >
> Okay, I've attached the separated patches.
> > and your code changes output to normal .png files, that is every
> > whatever.png is now a apng file, iam not sure this is what the user
> > expects / wants
> >
> I realised this might have been a problem too.
> However, I believe that when users want a normal PNG file out of ffmpeg
> (i.e., individual frames), they would usually be appending `%03d` or
> something similar, would that not be correct?

i think its quite a realistic use case to convert a single image
./ffmpeg -i lena.pnm lena.png

and while it may not make a big technical difference, i suspect
some people would find it rather hackish if that png file was a
APNG movie with a single frame

> When I tested this, if the `%03d` was included, ffmpeg automatically
> switched to PNG output mode, and when it was omitted, it was automatically
> Though, would it be a good idea to add a warning to the APNG muxer that
> it's running in APNG mode rather than normal PNG, and how the user can
> switch back (with `-f image2`)?

the code already buffers the first frame and writes it in the
trailer function so by the time the frame is actually written its
known if its a single frame or multi frame file and the single frame
case could use syntax identical to PNG
or is there some reason why a single image should be stored as APNG?
a option could be added to force single images to be APNG if that
has a usecase


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

What does censorship reveal? It reveals fear. -- Julian Assange
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