doc: add entry for APNG demuxer where needed.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Changelog

@@ -16,6 +16,7 @@ version <next>:
 - creating DASH compatible fragmented MP4, MPEG-DASH segmenting muxer
 - WebP muxer with animated WebP support
 - zygoaudio decoding support
+- APNG demuxer
 
 
 version 2.4:

MAINTAINERS

@@ -386,6 +386,7 @@ Muxers/Demuxers:
   aiffdec.c                             Baptiste Coudurier, Matthieu Bouron
   aiffenc.c                             Baptiste Coudurier, Matthieu Bouron
   ape.c                                 Kostya Shishkov
+  apngdec.c                             Benoit Fouet
   ass*                                  Aurelien Jacobs
   astdec.c                              Paul B Mahol
   astenc.c                              James Almer

doc/demuxers.texi

@@ -29,6 +29,26 @@ the caller can decide which variant streams to actually receive.
 The total bitrate of the variant that the stream belongs to is
 available in a metadata key named "variant_bitrate".
 
+@section apng
+
+Animated Portable Network Graphics demuxer.
+
+This demuxer is used to demux APNG files.
+All headers, but the PNG signature, up to (but not including) the first
+fcTL chunk are transmitted as extradata.
+Frames are then split as being all the chunks between two fcTL ones, or
+between the last fcTL and IEND chunks.
+
+@table @option
+@item -ignore_loop @var{bool}
+Ignore the loop variable in the file if set.
+@item -max_fps @var{int}
+Maximum framerate in frames per second (0 for no limit).
+@item -default_fps @var{int}
+Default framerate in frames per second when none is specified in the file
+(0 meaning as fast as possible).
+@end table
+
 @section asf
 
 Advanced Systems Format demuxer.