APNG support

[Granitosaurus]

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APNG is a animated png format that is becoming quite popular. pqiv however doesn't support displaying animations or at least animation_continue() does nothing.
Currently it's supported by major browsers and many applications - thus I think it would be addition to pqiv as well.

[phillipberndt]

libav supports apng. Could you check what happens if you disable all backends but ffmpeg/libav (see man page)?

If that works it might be as simple as hardcoding apng files to map to libav.

[Granitosaurus]

I'm getting this error:

$ pqiv ~/pictures/bugcat-sticker/55.apng --disable-backends=archive,archive_cbx,gdkpixbuf,poppler,spectre,webp,wand   
Didn't recognize file `/home/dex/pictures/bugcat-sticker/55.apng': Both its extension and MIME-type `image/png' are unknown. Fall-back to default file handler.
Segmentation fault (core dumped)

Seems like it's using gdkpixbuf backend for opening this apng file.

[Granitosaurus]

Any way to get around this?

[phillipberndt]

Sorry for the delay, and thanks for the reminder.

The same command works fine for me, and I can view an animated PNG. The core dump looks like there's something wrong either in pqiv or libav with the version you are using.

Are you familiar with debugging applications? If you can get your hands on a pqiv with debug symbols (when you compile yourself it'll have) you could generate a stacktrace for the crash, by running pqiv as gdb --args pqiv ~/pictures/bugcat-sticker/55.apng --disable-backends=archive,archive_cbx,gdkpixbuf,poppler,spectre,webp,wand and typing r<enter> to start it. Upon the crash, it'll fall back to a command line where you can generate a trace by typing bt<enter>.

If not, let me know which distribution (version) you have. I can send you a custom compiled binary with the necessary debugging information for me to make sense out of a stacktrace.