media/libpng/apng.patch
author Bryce Van Dyk <bvandyk@mozilla.com>
Wed, 26 Sep 2018 16:34:32 +0000
changeset 496769 e6f8e822851acb248df066141c3f2a6dcbad20d6
parent 495448 4e5643db5a23372cc1095c5ef60eca76b958c493
child 532453 179c0370dfa12b59d2214509d41a8356962f5df7
permissions -rw-r--r--
Bug 1494178 - Add check to ChromiumCDMChild to mark samples with 0 encrypted bytes as unencrypted. r=cpearce With the addition of an explicit encryption enum for CDM10 input data, if a sample has 0 encrypted bytes it must be marked as unencrypted. Historically we could let the CDM figure out based on the unencrypted + encrypted bytes. However, if we mark a sample as encrypted but it has 0 encrypted bytes, the CDM will fail to decrypt. This changeset adds a check to gracefully handle samples that are marked as encrypted but with no encrypted ranges. In such cases we mark the data as unencrypted and log that such data was encountered. This means we don't break playback of encrypted media should we overlook such cases, but have better detection via logging. Differential Revision: https://phabricator.services.mozilla.com/D6873

diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -7,8 +7,14 @@ COPYRIGHT NOTICE, DISCLAIMER, and LICENS
 
 If you modify libpng you may insert additional notices immediately following
 this sentence.
 
+This modified version of libpng code adds animated PNG support and is
+released under the libpng license described below. The modifications are
+Copyright (c) 2006-2007 Andrew Smith, Copyright (c) 2008-2017 Max Stepin,
+and are delimited by "#ifdef PNG_APNG_SUPPORTED / #endif" directives
+surrounding them in the modified libpng source files.
+
 This code is released under the libpng license.
 
 libpng versions 1.0.7, July 1, 2000 through 1.6.35, July 15, 2018 are
 Copyright (c) 2000-2002, 2004, 2006-2018 Glenn Randers-Pehrson, are
diff --git a/png.c b/png.c
--- a/png.c
+++ b/png.c
@@ -815,19 +815,23 @@ png_get_copyright(png_const_structrp png
    return PNG_STRING_COPYRIGHT
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
-      "libpng version 1.6.35 - July 15, 2018" PNG_STRING_NEWLINE \
+      "libpng version 1.6.35+apng - July 15, 2018" PNG_STRING_NEWLINE \
       "Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson" \
       PNG_STRING_NEWLINE \
       "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
       "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
-      PNG_STRING_NEWLINE;
+      PNG_STRING_NEWLINE \
+      "Portions Copyright (c) 2006-2007 Andrew Smith" PNG_STRING_NEWLINE \
+      "Portions Copyright (c) 2008-2018 Max Stepin" PNG_STRING_NEWLINE ;
 #  else
-   return "libpng version 1.6.35 - July 15, 2018\
+   return "libpng version 1.6.35+apng - July 15, 2018\
       Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
-      Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
+      Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.\
+      Portions Copyright (c) 2006-2007 Andrew Smith\
+      Portions Copyright (c) 2008-2018 Max Stepin";
 #  endif
 #endif
 }
 
diff --git a/png.h b/png.h
--- a/png.h
+++ b/png.h
@@ -22,8 +22,14 @@
  *
  * If you modify libpng you may insert additional notices immediately following
  * this sentence.
  *
+ * This modified version of libpng code adds animated PNG support and is
+ * released under the libpng license described below. The modifications are
+ * Copyright (c) 2006-2007 Andrew Smith, Copyright (c) 2008-2017 Max Stepin,
+ * and are delimited by "#ifdef PNG_APNG_SUPPORTED / #endif" directives
+ * surrounding them in the modified libpng source files.
+ *
  * This code is released under the libpng license.
  *
  * libpng versions 1.0.7, July 1, 2000 through 1.6.35, July 15, 2018 are
  * Copyright (c) 2000-2002, 2004, 2006-2018 Glenn Randers-Pehrson, are
@@ -308,10 +314,11 @@
  * skip to the end of this file and read the section entitled 'simplified API'.
  */
 
 /* Version information for png.h - this should match the version in png.c */
-#define PNG_LIBPNG_VER_STRING "1.6.35"
-#define PNG_HEADER_VERSION_STRING " libpng version 1.6.35 - July 15, 2018\n"
+#define PNG_LIBPNG_VER_STRING "1.6.35+apng"
+#define PNG_HEADER_VERSION_STRING \
+     " libpng version 1.6.35+apng - July 15, 2018\n"
 
 #define PNG_LIBPNG_VER_SONUM   16
 #define PNG_LIBPNG_VER_DLLNUM  16
 
@@ -360,8 +367,12 @@
  */
 #   include "pnglibconf.h"
 #endif
 
+#define PNG_APNG_SUPPORTED
+#define PNG_READ_APNG_SUPPORTED
+#define PNG_WRITE_APNG_SUPPORTED
+
 #ifndef PNG_VERSION_INFO_ONLY
 /* Machine specific configuration. */
 #  include "pngconf.h"
 #endif
@@ -455,8 +466,19 @@ extern "C" {
  * constants.
  * See pngconf.h for base types that vary by machine/system
  */
 
+#ifdef PNG_APNG_SUPPORTED
+/* dispose_op flags from inside fcTL */
+#define PNG_DISPOSE_OP_NONE        0x00
+#define PNG_DISPOSE_OP_BACKGROUND  0x01
+#define PNG_DISPOSE_OP_PREVIOUS    0x02
+
+/* blend_op flags from inside fcTL */
+#define PNG_BLEND_OP_SOURCE        0x00
+#define PNG_BLEND_OP_OVER          0x01
+#endif /* APNG */
+
 /* This triggers a compiler error in png.c, if png.c and png.h
  * do not agree upon the version number.
  */
 typedef char* png_libpng_version_1_6_35;
@@ -776,8 +798,12 @@ typedef png_unknown_chunk * * png_unknow
 #define PNG_INFO_sPLT 0x2000U  /* ESR, 1.0.6 */
 #define PNG_INFO_sCAL 0x4000U  /* ESR, 1.0.6 */
 #define PNG_INFO_IDAT 0x8000U  /* ESR, 1.0.6 */
 #define PNG_INFO_eXIf 0x10000U /* GR-P, 1.6.31 */
+#ifdef PNG_APNG_SUPPORTED
+#define PNG_INFO_acTL 0x20000U
+#define PNG_INFO_fcTL 0x40000U
+#endif
 
 /* This is used for the transformation routines, as some of them
  * change these values for the row.  It also should enable using
  * the routines for other purposes.
@@ -813,8 +839,12 @@ typedef PNG_CALLBACK(void, *png_write_st
 
 #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
 typedef PNG_CALLBACK(void, *png_progressive_info_ptr, (png_structp, png_infop));
 typedef PNG_CALLBACK(void, *png_progressive_end_ptr, (png_structp, png_infop));
+#ifdef PNG_APNG_SUPPORTED
+typedef PNG_CALLBACK(void, *png_progressive_frame_ptr, (png_structp,
+    png_uint_32));
+#endif
 
 /* The following callback receives png_uint_32 row_number, int pass for the
  * png_bytep data of the row.  When transforming an interlaced image the
  * row number is the row number within the sub-image of the interlace pass, so
@@ -3257,17 +3287,90 @@ PNG_EXPORT(244, int, png_set_option, (pn
 /*******************************************************************************
  *  END OF HARDWARE AND SOFTWARE OPTIONS
  ******************************************************************************/
 
+#ifdef PNG_APNG_SUPPORTED
+PNG_EXPORT(248, png_uint_32, png_get_acTL, (png_structp png_ptr,
+   png_infop info_ptr, png_uint_32 *num_frames, png_uint_32 *num_plays));
+
+PNG_EXPORT(249, png_uint_32, png_set_acTL, (png_structp png_ptr,
+   png_infop info_ptr, png_uint_32 num_frames, png_uint_32 num_plays));
+
+PNG_EXPORT(250, png_uint_32, png_get_num_frames, (png_structp png_ptr,
+   png_infop info_ptr));
+
+PNG_EXPORT(251, png_uint_32, png_get_num_plays, (png_structp png_ptr,
+   png_infop info_ptr));
+
+PNG_EXPORT(252, png_uint_32, png_get_next_frame_fcTL,
+   (png_structp png_ptr, png_infop info_ptr, png_uint_32 *width,
+   png_uint_32 *height, png_uint_32 *x_offset, png_uint_32 *y_offset,
+   png_uint_16 *delay_num, png_uint_16 *delay_den, png_byte *dispose_op,
+   png_byte *blend_op));
+
+PNG_EXPORT(253, png_uint_32, png_set_next_frame_fcTL,
+   (png_structp png_ptr, png_infop info_ptr, png_uint_32 width,
+   png_uint_32 height, png_uint_32 x_offset, png_uint_32 y_offset,
+   png_uint_16 delay_num, png_uint_16 delay_den, png_byte dispose_op,
+   png_byte blend_op));
+
+PNG_EXPORT(254, png_uint_32, png_get_next_frame_width,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(255, png_uint_32, png_get_next_frame_height,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(256, png_uint_32, png_get_next_frame_x_offset,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(257, png_uint_32, png_get_next_frame_y_offset,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(258, png_uint_16, png_get_next_frame_delay_num,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(259, png_uint_16, png_get_next_frame_delay_den,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(260, png_byte, png_get_next_frame_dispose_op,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(261, png_byte, png_get_next_frame_blend_op,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(262, png_byte, png_get_first_frame_is_hidden,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(263, png_uint_32, png_set_first_frame_is_hidden,
+   (png_structp png_ptr, png_infop info_ptr, png_byte is_hidden));
+
+#ifdef PNG_READ_APNG_SUPPORTED
+PNG_EXPORT(264, void, png_read_frame_head, (png_structp png_ptr,
+   png_infop info_ptr));
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+PNG_EXPORT(265, void, png_set_progressive_frame_fn, (png_structp png_ptr,
+   png_progressive_frame_ptr frame_info_fn,
+   png_progressive_frame_ptr frame_end_fn));
+#endif /* PROGRESSIVE_READ */
+#endif /* READ_APNG */
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+PNG_EXPORT(266, void, png_write_frame_head, (png_structp png_ptr,
+   png_infop info_ptr, png_bytepp row_pointers,
+   png_uint_32 width, png_uint_32 height,
+   png_uint_32 x_offset, png_uint_32 y_offset,
+   png_uint_16 delay_num, png_uint_16 delay_den, png_byte dispose_op,
+   png_byte blend_op));
+
+PNG_EXPORT(267, void, png_write_frame_tail, (png_structp png_ptr,
+   png_infop info_ptr));
+#endif /* WRITE_APNG */
+#endif /* APNG */
+
 /* Maintainer: Put new public prototypes here ^, in libpng.3, in project
  * defs, and in scripts/symbols.def.
  */
 
 /* The last ordinal number (this is the *last* one already used; the next
  * one to use is one more than this.)
  */
 #ifdef PNG_EXPORT_LAST_ORDINAL
+#ifdef PNG_APNG_SUPPORTED
+  PNG_EXPORT_LAST_ORDINAL(269);
+#else
   PNG_EXPORT_LAST_ORDINAL(249);
+#endif /* APNG */
 #endif
 
 #ifdef __cplusplus
 }
diff --git a/pngget.c b/pngget.c
--- a/pngget.c
+++ b/pngget.c
@@ -1245,5 +1245,167 @@ png_get_palette_max(png_const_structp pn
 }
 #  endif
 #endif
 
+#ifdef PNG_APNG_SUPPORTED
+png_uint_32 PNGAPI
+png_get_acTL(png_structp png_ptr, png_infop info_ptr,
+             png_uint_32 *num_frames, png_uint_32 *num_plays)
+{
+    png_debug1(1, "in %s retrieval function", "acTL");
+
+    if (png_ptr != NULL && info_ptr != NULL &&
+        (info_ptr->valid & PNG_INFO_acTL) != 0 &&
+        num_frames != NULL && num_plays != NULL)
+    {
+        *num_frames = info_ptr->num_frames;
+        *num_plays = info_ptr->num_plays;
+        return (1);
+    }
+
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_num_frames(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_num_frames()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->num_frames);
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_num_plays(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_num_plays()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->num_plays);
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_fcTL(png_structp png_ptr, png_infop info_ptr,
+             png_uint_32 *width, png_uint_32 *height,
+             png_uint_32 *x_offset, png_uint_32 *y_offset,
+             png_uint_16 *delay_num, png_uint_16 *delay_den,
+             png_byte *dispose_op, png_byte *blend_op)
+{
+    png_debug1(1, "in %s retrieval function", "fcTL");
+
+    if (png_ptr != NULL && info_ptr != NULL &&
+        (info_ptr->valid & PNG_INFO_fcTL) != 0 &&
+        width != NULL && height != NULL &&
+        x_offset != NULL && y_offset != NULL &&
+        delay_num != NULL && delay_den != NULL &&
+        dispose_op != NULL && blend_op != NULL)
+    {
+        *width = info_ptr->next_frame_width;
+        *height = info_ptr->next_frame_height;
+        *x_offset = info_ptr->next_frame_x_offset;
+        *y_offset = info_ptr->next_frame_y_offset;
+        *delay_num = info_ptr->next_frame_delay_num;
+        *delay_den = info_ptr->next_frame_delay_den;
+        *dispose_op = info_ptr->next_frame_dispose_op;
+        *blend_op = info_ptr->next_frame_blend_op;
+        return (1);
+    }
+
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_width(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_width()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_width);
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_height(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_height()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_height);
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_x_offset(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_x_offset()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_x_offset);
+    return (0);
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_y_offset(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_y_offset()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_y_offset);
+    return (0);
+}
+
+png_uint_16 PNGAPI
+png_get_next_frame_delay_num(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_delay_num()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_delay_num);
+    return (0);
+}
+
+png_uint_16 PNGAPI
+png_get_next_frame_delay_den(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_delay_den()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_delay_den);
+    return (0);
+}
+
+png_byte PNGAPI
+png_get_next_frame_dispose_op(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_dispose_op()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_dispose_op);
+    return (0);
+}
+
+png_byte PNGAPI
+png_get_next_frame_blend_op(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_get_next_frame_blend_op()");
+
+    if (png_ptr != NULL && info_ptr != NULL)
+        return (info_ptr->next_frame_blend_op);
+    return (0);
+}
+
+png_byte PNGAPI
+png_get_first_frame_is_hidden(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_first_frame_is_hidden()");
+
+    if (png_ptr != NULL)
+       return (png_byte)(png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN);
+
+    PNG_UNUSED(info_ptr)
+
+    return 0;
+}
+#endif /* APNG */
 #endif /* READ || WRITE */
diff --git a/pnginfo.h b/pnginfo.h
--- a/pnginfo.h
+++ b/pnginfo.h
@@ -262,6 +262,19 @@ defined(PNG_READ_BACKGROUND_SUPPORTED)
    /* Data valid if (valid & PNG_INFO_IDAT) non-zero */
    png_bytepp row_pointers;        /* the image bits */
 #endif
 
+#ifdef PNG_APNG_SUPPORTED
+   png_uint_32 num_frames; /* including default image */
+   png_uint_32 num_plays;
+   png_uint_32 next_frame_width;
+   png_uint_32 next_frame_height;
+   png_uint_32 next_frame_x_offset;
+   png_uint_32 next_frame_y_offset;
+   png_uint_16 next_frame_delay_num;
+   png_uint_16 next_frame_delay_den;
+   png_byte next_frame_dispose_op;
+   png_byte next_frame_blend_op;
+#endif
+
 };
 #endif /* PNGINFO_H */
diff --git a/pngpread.c b/pngpread.c
--- a/pngpread.c
+++ b/pngpread.c
@@ -194,8 +194,91 @@ png_push_read_chunk(png_structrp png_ptr
    }
 
    chunk_name = png_ptr->chunk_name;
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   if (png_ptr->num_frames_read > 0 &&
+       png_ptr->num_frames_read < info_ptr->num_frames)
+   {
+      if (chunk_name == png_IDAT)
+      {
+         /* Discard trailing IDATs for the first frame */
+         if ((png_ptr->mode & PNG_HAVE_fcTL) != 0 ||
+             png_ptr->num_frames_read > 1)
+            png_error(png_ptr, "out of place IDAT");
+
+         PNG_PUSH_SAVE_BUFFER_IF_FULL
+         png_crc_finish(png_ptr, png_ptr->push_length);
+         png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+      }
+
+      else if (chunk_name == png_fdAT)
+      {
+         PNG_PUSH_SAVE_BUFFER_IF_LT(4)
+         png_ensure_sequence_number(png_ptr, 4);
+
+         if ((png_ptr->mode & PNG_HAVE_fcTL) == 0)
+         {
+            /* Discard trailing fdATs for frames other than the first */
+            if (png_ptr->num_frames_read < 2)
+               png_error(png_ptr, "out of place fdAT");
+
+            PNG_PUSH_SAVE_BUFFER_IF_FULL
+            png_crc_finish(png_ptr, png_ptr->push_length);
+            png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+         }
+
+         else
+         {
+            /* frame data follows */
+            png_ptr->idat_size = png_ptr->push_length - 4;
+            png_ptr->mode |= PNG_HAVE_IDAT;
+            png_ptr->process_mode = PNG_READ_IDAT_MODE;
+         }
+      }
+
+      else if (chunk_name == png_fcTL)
+      {
+         PNG_PUSH_SAVE_BUFFER_IF_FULL
+         png_read_reset(png_ptr);
+         png_ptr->mode &= ~PNG_HAVE_fcTL;
+
+         png_handle_fcTL(png_ptr, info_ptr, png_ptr->push_length);
+
+         if ((png_ptr->mode & PNG_HAVE_fcTL) == 0)
+            png_error(png_ptr, "missing required fcTL chunk");
+
+         png_read_reinit(png_ptr, info_ptr);
+         png_progressive_read_reset(png_ptr);
+
+         if (png_ptr->frame_info_fn != NULL)
+            (*(png_ptr->frame_info_fn))(png_ptr, png_ptr->num_frames_read);
+
+         png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+      }
+
+      else if (chunk_name == png_IEND)
+      {
+         PNG_PUSH_SAVE_BUFFER_IF_FULL
+         png_warning(png_ptr, "Number of actual frames fewer than expected");
+         png_crc_finish(png_ptr, png_ptr->push_length);
+         png_ptr->process_mode = PNG_READ_DONE_MODE;
+         png_push_have_end(png_ptr, info_ptr);
+      }
+
+      else
+      {
+         PNG_PUSH_SAVE_BUFFER_IF_FULL
+         png_warning(png_ptr, "Skipped (ignored) a chunk "
+                              "between APNG chunks");
+         png_crc_finish(png_ptr, png_ptr->push_length);
+         png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+      }
+
+      return;
+   }
+#endif /* READ_APNG */
+
    if (chunk_name == png_IDAT)
    {
       if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
          png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;
@@ -260,8 +343,11 @@ png_push_read_chunk(png_structrp png_ptr
    }
 
    else if (chunk_name == png_IDAT)
    {
+#ifdef PNG_READ_APNG_SUPPORTED
+      png_have_info(png_ptr, info_ptr);
+#endif
       png_ptr->idat_size = png_ptr->push_length;
       png_ptr->process_mode = PNG_READ_IDAT_MODE;
       png_push_have_info(png_ptr, info_ptr);
       png_ptr->zstream.avail_out =
@@ -406,8 +492,22 @@ png_push_read_chunk(png_structrp png_ptr
       png_handle_iTXt(png_ptr, info_ptr, png_ptr->push_length);
    }
 #endif
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   else if (chunk_name == png_acTL)
+   {
+      PNG_PUSH_SAVE_BUFFER_IF_FULL
+      png_handle_acTL(png_ptr, info_ptr, png_ptr->push_length);
+   }
+
+   else if (chunk_name == png_fcTL)
+   {
+      PNG_PUSH_SAVE_BUFFER_IF_FULL
+      png_handle_fcTL(png_ptr, info_ptr, png_ptr->push_length);
+   }
+
+#endif /* READ_APNG */
    else
    {
       PNG_PUSH_SAVE_BUFFER_IF_FULL
       png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length,
@@ -538,27 +638,74 @@ png_push_read_IDAT(png_structrp png_ptr)
       png_byte chunk_length[4];
       png_byte chunk_tag[4];
 
       /* TODO: this code can be commoned up with the same code in push_read */
+#ifdef PNG_READ_APNG_SUPPORTED
+      PNG_PUSH_SAVE_BUFFER_IF_LT(12)
+#else
       PNG_PUSH_SAVE_BUFFER_IF_LT(8)
+#endif
       png_push_fill_buffer(png_ptr, chunk_length, 4);
       png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
       png_reset_crc(png_ptr);
       png_crc_read(png_ptr, chunk_tag, 4);
       png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
       png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
 
+#ifdef PNG_READ_APNG_SUPPORTED
+      if (png_ptr->chunk_name != png_fdAT && png_ptr->num_frames_read > 0)
+      {
+          if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) != 0)
+          {
+              png_ptr->process_mode = PNG_READ_CHUNK_MODE;
+              if (png_ptr->frame_end_fn != NULL)
+                 (*(png_ptr->frame_end_fn))(png_ptr, png_ptr->num_frames_read);
+              png_ptr->num_frames_read++;
+              return;
+          }
+          else
+          {
+              if (png_ptr->chunk_name == png_IEND)
+                  png_error(png_ptr, "Not enough image data");
+              PNG_PUSH_SAVE_BUFFER_IF_FULL
+              png_warning(png_ptr, "Skipping (ignoring) a chunk between "
+                                   "APNG chunks");
+              png_crc_finish(png_ptr, png_ptr->push_length);
+              png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+              return;
+          }
+      }
+      else
+#endif
+#ifdef PNG_READ_APNG_SUPPORTED
+      if (png_ptr->chunk_name != png_IDAT && png_ptr->num_frames_read == 0)
+#else
       if (png_ptr->chunk_name != png_IDAT)
+#endif
       {
          png_ptr->process_mode = PNG_READ_CHUNK_MODE;
 
          if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
             png_error(png_ptr, "Not enough compressed data");
 
+#ifdef PNG_READ_APNG_SUPPORTED
+         if (png_ptr->frame_end_fn != NULL)
+            (*(png_ptr->frame_end_fn))(png_ptr, png_ptr->num_frames_read);
+         png_ptr->num_frames_read++;
+#endif
+
          return;
       }
 
       png_ptr->idat_size = png_ptr->push_length;
+
+#ifdef PNG_READ_APNG_SUPPORTED
+      if (png_ptr->num_frames_read > 0)
+      {
+         png_ensure_sequence_number(png_ptr, 4);
+         png_ptr->idat_size -= 4;
+      }
+#endif
    }
 
    if (png_ptr->idat_size != 0 && png_ptr->save_buffer_size != 0)
    {
@@ -630,8 +777,18 @@ png_process_IDAT_data(png_structrp png_p
    /* The caller checks for a non-zero buffer length. */
    if (!(buffer_length > 0) || buffer == NULL)
       png_error(png_ptr, "No IDAT data (internal error)");
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   /* If the app is not APNG-aware, decode only the first frame */
+   if ((png_ptr->apng_flags & PNG_APNG_APP) == 0 &&
+      png_ptr->num_frames_read > 0)
+   {
+      png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
+      return;
+   }
+#endif
+
    /* This routine must process all the data it has been given
     * before returning, calling the row callback as required to
     * handle the uncompressed results.
     */
@@ -1084,8 +1241,20 @@ png_set_progressive_read_fn(png_structrp
 
    png_set_read_fn(png_ptr, progressive_ptr, png_push_fill_buffer);
 }
 
+#ifdef PNG_READ_APNG_SUPPORTED
+void PNGAPI
+png_set_progressive_frame_fn(png_structp png_ptr,
+   png_progressive_frame_ptr frame_info_fn,
+   png_progressive_frame_ptr frame_end_fn)
+{
+   png_ptr->frame_info_fn = frame_info_fn;
+   png_ptr->frame_end_fn = frame_end_fn;
+   png_ptr->apng_flags |= PNG_APNG_APP;
+}
+#endif
+
 png_voidp PNGAPI
 png_get_progressive_ptr(png_const_structrp png_ptr)
 {
    if (png_ptr == NULL)
diff --git a/pngpriv.h b/pngpriv.h
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -633,8 +633,12 @@
 #define PNG_HAVE_PNG_SIGNATURE    0x1000U
 #define PNG_HAVE_CHUNK_AFTER_IDAT 0x2000U /* Have another chunk after IDAT */
                    /*             0x4000U (unused) */
 #define PNG_IS_READ_STRUCT        0x8000U /* Else is a write struct */
+#ifdef PNG_APNG_SUPPORTED
+#define PNG_HAVE_acTL            0x10000U
+#define PNG_HAVE_fcTL            0x20000U
+#endif
 
 /* Flags for the transformations the PNG library does on the image data */
 #define PNG_BGR                 0x0001U
 #define PNG_INTERLACE           0x0002U
@@ -869,8 +873,18 @@
 #define png_tIME PNG_U32(116,  73,  77,  69)
 #define png_tRNS PNG_U32(116,  82,  78,  83)
 #define png_zTXt PNG_U32(122,  84,  88, 116)
 
+#ifdef PNG_APNG_SUPPORTED
+#define png_acTL PNG_U32( 97,  99,  84,  76)
+#define png_fcTL PNG_U32(102,  99,  84,  76)
+#define png_fdAT PNG_U32(102, 100,  65,  84)
+
+/* For png_struct.apng_flags: */
+#define PNG_FIRST_FRAME_HIDDEN       0x0001U
+#define PNG_APNG_APP                 0x0002U
+#endif
+
 /* The following will work on (signed char*) strings, whereas the get_uint_32
  * macro will fail on top-bit-set values because of the sign extension.
  */
 #define PNG_CHUNK_FROM_STRING(s)\
@@ -1620,8 +1634,51 @@ PNG_INTERNAL_FUNCTION(void,png_push_read
 #  endif
 
 #endif /* PROGRESSIVE_READ */
 
+#ifdef PNG_APNG_SUPPORTED
+PNG_INTERNAL_FUNCTION(void,png_ensure_fcTL_is_valid,(png_structp png_ptr,
+   png_uint_32 width, png_uint_32 height,
+   png_uint_32 x_offset, png_uint_32 y_offset,
+   png_uint_16 delay_num, png_uint_16 delay_den,
+   png_byte dispose_op, png_byte blend_op),PNG_EMPTY);
+
+#ifdef PNG_READ_APNG_SUPPORTED
+PNG_INTERNAL_FUNCTION(void,png_handle_acTL,(png_structp png_ptr,
+   png_infop info_ptr, png_uint_32 length),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_handle_fcTL,(png_structp png_ptr,
+   png_infop info_ptr, png_uint_32 length),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_handle_fdAT,(png_structp png_ptr,
+   png_infop info_ptr, png_uint_32 length),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_have_info,(png_structp png_ptr,
+   png_infop info_ptr),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_ensure_sequence_number,(png_structp png_ptr,
+   png_uint_32 length),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_read_reset,(png_structp png_ptr),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_read_reinit,(png_structp png_ptr,
+   png_infop info_ptr),PNG_EMPTY);
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+PNG_INTERNAL_FUNCTION(void,png_progressive_read_reset,(png_structp png_ptr),
+   PNG_EMPTY);
+#endif /* PROGRESSIVE_READ */
+#endif /* READ_APNG */
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+PNG_INTERNAL_FUNCTION(void,png_write_acTL,(png_structp png_ptr,
+   png_uint_32 num_frames, png_uint_32 num_plays),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_write_fcTL,(png_structp png_ptr,
+   png_uint_32 width, png_uint_32 height,
+   png_uint_32 x_offset, png_uint_32 y_offset,
+   png_uint_16 delay_num, png_uint_16 delay_den,
+   png_byte dispose_op, png_byte blend_op),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_write_fdAT,(png_structp png_ptr,
+   png_const_bytep data, png_size_t length),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_write_reset,(png_structp png_ptr),PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void,png_write_reinit,(png_structp png_ptr,
+   png_infop info_ptr, png_uint_32 width, png_uint_32 height),PNG_EMPTY);
+#endif /* WRITE_APNG */
+#endif /* APNG */
+
 /* Added at libpng version 1.6.0 */
 #ifdef PNG_GAMMA_SUPPORTED
 PNG_INTERNAL_FUNCTION(void,png_colorspace_set_gamma,(png_const_structrp png_ptr,
     png_colorspacerp colorspace, png_fixed_point gAMA), PNG_EMPTY);
diff --git a/pngread.c b/pngread.c
--- a/pngread.c
+++ b/pngread.c
@@ -160,8 +160,11 @@ png_read_info(png_structrp png_ptr, png_
          png_handle_PLTE(png_ptr, info_ptr, length);
 
       else if (chunk_name == png_IDAT)
       {
+#ifdef PNG_READ_APNG_SUPPORTED
+         png_have_info(png_ptr, info_ptr);
+#endif
          png_ptr->idat_size = length;
          break;
       }
 
@@ -254,15 +257,92 @@ png_read_info(png_structrp png_ptr, png_
       else if (chunk_name == png_iTXt)
          png_handle_iTXt(png_ptr, info_ptr, length);
 #endif
 
+#ifdef PNG_READ_APNG_SUPPORTED
+      else if (chunk_name == png_acTL)
+         png_handle_acTL(png_ptr, info_ptr, length);
+
+      else if (chunk_name == png_fcTL)
+         png_handle_fcTL(png_ptr, info_ptr, length);
+
+      else if (chunk_name == png_fdAT)
+         png_handle_fdAT(png_ptr, info_ptr, length);
+#endif
+
       else
          png_handle_unknown(png_ptr, info_ptr, length,
              PNG_HANDLE_CHUNK_AS_DEFAULT);
    }
 }
 #endif /* SEQUENTIAL_READ */
 
+#ifdef PNG_READ_APNG_SUPPORTED
+void PNGAPI
+png_read_frame_head(png_structp png_ptr, png_infop info_ptr)
+{
+    png_byte have_chunk_after_DAT; /* after IDAT or after fdAT */
+
+    png_debug(0, "Reading frame head");
+
+    if ((png_ptr->mode & PNG_HAVE_acTL) == 0)
+        png_error(png_ptr, "attempt to png_read_frame_head() but "
+                           "no acTL present");
+
+    /* do nothing for the main IDAT */
+    if (png_ptr->num_frames_read == 0)
+        return;
+
+    png_read_reset(png_ptr);
+    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
+    png_ptr->mode &= ~PNG_HAVE_fcTL;
+
+    have_chunk_after_DAT = 0;
+    for (;;)
+    {
+        png_uint_32 length = png_read_chunk_header(png_ptr);
+
+        if (png_ptr->chunk_name == png_IDAT)
+        {
+            /* discard trailing IDATs for the first frame */
+            if (have_chunk_after_DAT != 0 || png_ptr->num_frames_read > 1)
+                png_error(png_ptr, "png_read_frame_head(): out of place IDAT");
+            png_crc_finish(png_ptr, length);
+        }
+
+        else if (png_ptr->chunk_name == png_fcTL)
+        {
+            png_handle_fcTL(png_ptr, info_ptr, length);
+            have_chunk_after_DAT = 1;
+        }
+
+        else if (png_ptr->chunk_name == png_fdAT)
+        {
+            png_ensure_sequence_number(png_ptr, length);
+
+            /* discard trailing fdATs for frames other than the first */
+            if (have_chunk_after_DAT == 0 && png_ptr->num_frames_read > 1)
+                png_crc_finish(png_ptr, length - 4);
+            else if (png_ptr->mode & PNG_HAVE_fcTL)
+            {
+                png_ptr->idat_size = length - 4;
+                png_ptr->mode |= PNG_HAVE_IDAT;
+
+                break;
+            }
+            else
+                png_error(png_ptr, "png_read_frame_head(): out of place fdAT");
+        }
+        else
+        {
+            png_warning(png_ptr, "Skipped (ignored) a chunk "
+                                 "between APNG chunks");
+            png_crc_finish(png_ptr, length);
+        }
+    }
+}
+#endif /* READ_APNG */
+
 /* Optional call to update the users info_ptr structure */
 void PNGAPI
 png_read_update_info(png_structrp png_ptr, png_inforp info_ptr)
 {
diff --git a/pngrutil.c b/pngrutil.c
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -864,8 +864,13 @@ png_handle_IHDR(png_structrp png_ptr, pn
    compression_type = buf[10];
    filter_type = buf[11];
    interlace_type = buf[12];
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   png_ptr->first_frame_width = width;
+   png_ptr->first_frame_height = height;
+#endif
+
    /* Set internal variables */
    png_ptr->width = width;
    png_ptr->height = height;
    png_ptr->bit_depth = (png_byte)bit_depth;
@@ -2857,8 +2862,182 @@ png_handle_iTXt(png_structrp png_ptr, pn
       png_chunk_benign_error(png_ptr, errmsg);
 }
 #endif
 
+#ifdef PNG_READ_APNG_SUPPORTED
+void /* PRIVATE */
+png_handle_acTL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
+{
+    png_byte data[8];
+    png_uint_32 num_frames;
+    png_uint_32 num_plays;
+    png_uint_32 didSet;
+
+    png_debug(1, "in png_handle_acTL");
+
+    if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
+    {
+        png_error(png_ptr, "Missing IHDR before acTL");
+    }
+    else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
+    {
+        png_warning(png_ptr, "Invalid acTL after IDAT skipped");
+        png_crc_finish(png_ptr, length);
+        return;
+    }
+    else if ((png_ptr->mode & PNG_HAVE_acTL) != 0)
+    {
+        png_warning(png_ptr, "Duplicate acTL skipped");
+        png_crc_finish(png_ptr, length);
+        return;
+    }
+    else if (length != 8)
+    {
+        png_warning(png_ptr, "acTL with invalid length skipped");
+        png_crc_finish(png_ptr, length);
+        return;
+    }
+
+    png_crc_read(png_ptr, data, 8);
+    png_crc_finish(png_ptr, 0);
+
+    num_frames = png_get_uint_31(png_ptr, data);
+    num_plays = png_get_uint_31(png_ptr, data + 4);
+
+    /* the set function will do error checking on num_frames */
+    didSet = png_set_acTL(png_ptr, info_ptr, num_frames, num_plays);
+    if (didSet != 0)
+        png_ptr->mode |= PNG_HAVE_acTL;
+}
+
+void /* PRIVATE */
+png_handle_fcTL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
+{
+    png_byte data[22];
+    png_uint_32 width;
+    png_uint_32 height;
+    png_uint_32 x_offset;
+    png_uint_32 y_offset;
+    png_uint_16 delay_num;
+    png_uint_16 delay_den;
+    png_byte dispose_op;
+    png_byte blend_op;
+
+    png_debug(1, "in png_handle_fcTL");
+
+    png_ensure_sequence_number(png_ptr, length);
+
+    if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
+    {
+        png_error(png_ptr, "Missing IHDR before fcTL");
+    }
+    else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
+    {
+        /* for any frames other then the first this message may be misleading,
+        * but correct. PNG_HAVE_IDAT is unset before the frame head is read
+        * i can't think of a better message */
+        png_warning(png_ptr, "Invalid fcTL after IDAT skipped");
+        png_crc_finish(png_ptr, length-4);
+        return;
+    }
+    else if ((png_ptr->mode & PNG_HAVE_fcTL) != 0)
+    {
+        png_warning(png_ptr, "Duplicate fcTL within one frame skipped");
+        png_crc_finish(png_ptr, length-4);
+        return;
+    }
+    else if (length != 26)
+    {
+        png_warning(png_ptr, "fcTL with invalid length skipped");
+        png_crc_finish(png_ptr, length-4);
+        return;
+    }
+
+    png_crc_read(png_ptr, data, 22);
+    png_crc_finish(png_ptr, 0);
+
+    width = png_get_uint_31(png_ptr, data);
+    height = png_get_uint_31(png_ptr, data + 4);
+    x_offset = png_get_uint_31(png_ptr, data + 8);
+    y_offset = png_get_uint_31(png_ptr, data + 12);
+    delay_num = png_get_uint_16(data + 16);
+    delay_den = png_get_uint_16(data + 18);
+    dispose_op = data[20];
+    blend_op = data[21];
+
+    if (png_ptr->num_frames_read == 0 && (x_offset != 0 || y_offset != 0))
+    {
+        png_warning(png_ptr, "fcTL for the first frame must have zero offset");
+        return;
+    }
+
+    if (info_ptr != NULL)
+    {
+        if (png_ptr->num_frames_read == 0 &&
+            (width != info_ptr->width || height != info_ptr->height))
+        {
+            png_warning(png_ptr, "size in first frame's fcTL must match "
+                               "the size in IHDR");
+            return;
+        }
+
+        /* The set function will do more error checking */
+        png_set_next_frame_fcTL(png_ptr, info_ptr, width, height,
+                                x_offset, y_offset, delay_num, delay_den,
+                                dispose_op, blend_op);
+
+        png_read_reinit(png_ptr, info_ptr);
+
+        png_ptr->mode |= PNG_HAVE_fcTL;
+    }
+}
+
+void /* PRIVATE */
+png_have_info(png_structp png_ptr, png_infop info_ptr)
+{
+    if ((info_ptr->valid & PNG_INFO_acTL) != 0 &&
+        (info_ptr->valid & PNG_INFO_fcTL) == 0)
+    {
+        png_ptr->apng_flags |= PNG_FIRST_FRAME_HIDDEN;
+        info_ptr->num_frames++;
+    }
+}
+
+void /* PRIVATE */
+png_handle_fdAT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
+{
+    png_ensure_sequence_number(png_ptr, length);
+
+    /* This function is only called from png_read_end(), png_read_info(),
+    * and png_push_read_chunk() which means that:
+    * - the user doesn't want to read this frame
+    * - or this is an out-of-place fdAT
+    * in either case it is safe to ignore the chunk with a warning */
+    png_warning(png_ptr, "ignoring fdAT chunk");
+    png_crc_finish(png_ptr, length - 4);
+    PNG_UNUSED(info_ptr)
+}
+
+void /* PRIVATE */
+png_ensure_sequence_number(png_structp png_ptr, png_uint_32 length)
+{
+    png_byte data[4];
+    png_uint_32 sequence_number;
+
+    if (length < 4)
+        png_error(png_ptr, "invalid fcTL or fdAT chunk found");
+
+    png_crc_read(png_ptr, data, 4);
+    sequence_number = png_get_uint_31(png_ptr, data);
+
+    if (sequence_number != png_ptr->next_seq_num)
+        png_error(png_ptr, "fcTL or fdAT chunk with out-of-order sequence "
+                           "number found");
+
+    png_ptr->next_seq_num++;
+}
+#endif /* READ_APNG */
+
 #ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
 /* Utility function for png_handle_unknown; set up png_ptr::unknown_chunk */
 static int
 png_cache_unknown_chunk(png_structrp png_ptr, png_uint_32 length)
@@ -3162,9 +3341,13 @@ png_check_chunk_length(png_const_structr
 # elif PNG_USER_CHUNK_MALLOC_MAX > 0
    if (PNG_USER_CHUNK_MALLOC_MAX < limit)
       limit = PNG_USER_CHUNK_MALLOC_MAX;
 # endif
+#ifdef PNG_READ_APNG_SUPPORTED
+   if (png_ptr->chunk_name == png_IDAT || png_ptr->chunk_name == png_fdAT)
+#else
    if (png_ptr->chunk_name == png_IDAT)
+#endif
    {
       png_alloc_size_t idat_limit = PNG_UINT_31_MAX;
       size_t row_factor =
          (size_t)png_ptr->width
@@ -4166,8 +4349,40 @@ png_read_IDAT_data(png_structrp png_ptr,
       {
          uInt avail_in;
          png_bytep buffer;
 
+#ifdef PNG_READ_APNG_SUPPORTED
+         png_uint_32 bytes_to_skip = 0;
+
+         while (png_ptr->idat_size == 0 || bytes_to_skip != 0)
+         {
+            png_crc_finish(png_ptr, bytes_to_skip);
+            bytes_to_skip = 0;
+
+            png_ptr->idat_size = png_read_chunk_header(png_ptr);
+            if (png_ptr->num_frames_read == 0)
+            {
+               if (png_ptr->chunk_name != png_IDAT)
+                  png_error(png_ptr, "Not enough image data");
+            }
+            else
+            {
+               if (png_ptr->chunk_name == png_IEND)
+                  png_error(png_ptr, "Not enough image data");
+               if (png_ptr->chunk_name != png_fdAT)
+               {
+                  png_warning(png_ptr, "Skipped (ignored) a chunk "
+                                       "between APNG chunks");
+                  bytes_to_skip = png_ptr->idat_size;
+                  continue;
+               }
+
+               png_ensure_sequence_number(png_ptr, png_ptr->idat_size);
+
+               png_ptr->idat_size -= 4;
+            }
+         }
+#else
          while (png_ptr->idat_size == 0)
          {
             png_crc_finish(png_ptr, 0);
 
@@ -4177,8 +4392,9 @@ png_read_IDAT_data(png_structrp png_ptr,
              */
             if (png_ptr->chunk_name != png_IDAT)
                png_error(png_ptr, "Not enough image data");
          }
+#endif /* READ_APNG */
 
          avail_in = png_ptr->IDAT_read_size;
 
          if (avail_in > png_ptr->idat_size)
@@ -4240,8 +4456,11 @@ png_read_IDAT_data(png_structrp png_ptr,
          png_ptr->zstream.next_out = NULL;
 
          png_ptr->mode |= PNG_AFTER_IDAT;
          png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
+#ifdef PNG_READ_APNG_SUPPORTED
+         png_ptr->num_frames_read++;
+#endif
 
          if (png_ptr->zstream.avail_in > 0 || png_ptr->idat_size > 0)
             png_chunk_benign_error(png_ptr, "Extra compressed data");
          break;
@@ -4678,5 +4897,81 @@ defined(PNG_USER_TRANSFORM_PTR_SUPPORTED
       png_error(png_ptr, png_ptr->zstream.msg);
 
    png_ptr->flags |= PNG_FLAG_ROW_INIT;
 }
+
+#ifdef PNG_READ_APNG_SUPPORTED
+/* This function is to be called after the main IDAT set has been read and
+ * before a new IDAT is read. It resets some parts of png_ptr
+ * to make them usable by the read functions again */
+void /* PRIVATE */
+png_read_reset(png_structp png_ptr)
+{
+    png_ptr->mode &= ~PNG_HAVE_IDAT;
+    png_ptr->mode &= ~PNG_AFTER_IDAT;
+    png_ptr->row_number = 0;
+    png_ptr->pass = 0;
+}
+
+void /* PRIVATE */
+png_read_reinit(png_structp png_ptr, png_infop info_ptr)
+{
+    png_ptr->width = info_ptr->next_frame_width;
+    png_ptr->height = info_ptr->next_frame_height;
+    png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth,png_ptr->width);
+    png_ptr->info_rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth,
+        png_ptr->width);
+    if (png_ptr->prev_row != NULL)
+        memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
+}
+
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+/* same as png_read_reset() but for the progressive reader */
+void /* PRIVATE */
+png_progressive_read_reset(png_structp png_ptr)
+{
+#ifdef PNG_READ_INTERLACING_SUPPORTED
+    /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
+
+    /* Start of interlace block */
+    static PNG_CONST png_byte png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};
+
+    /* Offset to next interlace block */
+    static PNG_CONST png_byte png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};
+
+    /* Start of interlace block in the y direction */
+    static PNG_CONST png_byte png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};
+
+    /* Offset to next interlace block in the y direction */
+    static PNG_CONST png_byte png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};
+
+    if (png_ptr->interlaced != 0)
+    {
+        if ((png_ptr->transformations & PNG_INTERLACE) == 0)
+            png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
+                                png_pass_ystart[0]) / png_pass_yinc[0];
+        else
+            png_ptr->num_rows = png_ptr->height;
+
+        png_ptr->iwidth = (png_ptr->width +
+                           png_pass_inc[png_ptr->pass] - 1 -
+                           png_pass_start[png_ptr->pass]) /
+                           png_pass_inc[png_ptr->pass];
+    }
+    else
+#endif /* READ_INTERLACING */
+    {
+        png_ptr->num_rows = png_ptr->height;
+        png_ptr->iwidth = png_ptr->width;
+    }
+    png_ptr->flags &= ~PNG_FLAG_ZSTREAM_ENDED;
+    if (inflateReset(&(png_ptr->zstream)) != Z_OK)
+        png_error(png_ptr, "inflateReset failed");
+    png_ptr->zstream.avail_in = 0;
+    png_ptr->zstream.next_in = 0;
+    png_ptr->zstream.next_out = png_ptr->row_buf;
+    png_ptr->zstream.avail_out = (uInt)PNG_ROWBYTES(png_ptr->pixel_depth,
+        png_ptr->iwidth) + 1;
+}
+#endif /* PROGRESSIVE_READ */
+#endif /* READ_APNG */
 #endif /* READ */
diff --git a/pngset.c b/pngset.c
--- a/pngset.c
+++ b/pngset.c
@@ -287,8 +287,13 @@ png_set_IHDR(png_const_structrp png_ptr,
 
    info_ptr->pixel_depth = (png_byte)(info_ptr->channels * info_ptr->bit_depth);
 
    info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, width);
+
+#ifdef PNG_APNG_SUPPORTED
+   /* for non-animated png. this may be overwritten from an acTL chunk later */
+   info_ptr->num_frames = 1;
+#endif
 }
 
 #ifdef PNG_oFFs_SUPPORTED
 void PNGAPI
@@ -1157,8 +1162,148 @@ png_set_sPLT(png_const_structrp png_ptr,
       png_chunk_report(png_ptr, "sPLT out of memory", PNG_CHUNK_WRITE_ERROR);
 }
 #endif /* sPLT */
 
+#ifdef PNG_APNG_SUPPORTED
+png_uint_32 PNGAPI
+png_set_acTL(png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 num_frames, png_uint_32 num_plays)
+{
+    png_debug1(1, "in %s storage function", "acTL");
+
+    if (png_ptr == NULL || info_ptr == NULL)
+    {
+        png_warning(png_ptr,
+                    "Call to png_set_acTL() with NULL png_ptr "
+                    "or info_ptr ignored");
+        return (0);
+    }
+    if (num_frames == 0)
+    {
+        png_warning(png_ptr,
+                    "Ignoring attempt to set acTL with num_frames zero");
+        return (0);
+    }
+    if (num_frames > PNG_UINT_31_MAX)
+    {
+        png_warning(png_ptr,
+                    "Ignoring attempt to set acTL with num_frames > 2^31-1");
+        return (0);
+    }
+    if (num_plays > PNG_UINT_31_MAX)
+    {
+        png_warning(png_ptr,
+                    "Ignoring attempt to set acTL with num_plays > 2^31-1");
+        return (0);
+    }
+
+    info_ptr->num_frames = num_frames;
+    info_ptr->num_plays = num_plays;
+
+    info_ptr->valid |= PNG_INFO_acTL;
+
+    return (1);
+}
+
+/* delay_num and delay_den can hold any 16-bit values including zero */
+png_uint_32 PNGAPI
+png_set_next_frame_fcTL(png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den,
+    png_byte dispose_op, png_byte blend_op)
+{
+    png_debug1(1, "in %s storage function", "fcTL");
+
+    if (png_ptr == NULL || info_ptr == NULL)
+    {
+        png_warning(png_ptr,
+                    "Call to png_set_fcTL() with NULL png_ptr or info_ptr "
+                    "ignored");
+        return (0);
+    }
+
+    png_ensure_fcTL_is_valid(png_ptr, width, height, x_offset, y_offset,
+                             delay_num, delay_den, dispose_op, blend_op);
+
+    if (blend_op == PNG_BLEND_OP_OVER)
+    {
+        if ((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) == 0 &&
+            png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) == 0)
+        {
+          png_warning(png_ptr, "PNG_BLEND_OP_OVER is meaningless "
+                               "and wasteful for opaque images, ignored");
+          blend_op = PNG_BLEND_OP_SOURCE;
+        }
+    }
+
+    info_ptr->next_frame_width = width;
+    info_ptr->next_frame_height = height;
+    info_ptr->next_frame_x_offset = x_offset;
+    info_ptr->next_frame_y_offset = y_offset;
+    info_ptr->next_frame_delay_num = delay_num;
+    info_ptr->next_frame_delay_den = delay_den;
+    info_ptr->next_frame_dispose_op = dispose_op;
+    info_ptr->next_frame_blend_op = blend_op;
+
+    info_ptr->valid |= PNG_INFO_fcTL;
+
+    return (1);
+}
+
+void /* PRIVATE */
+png_ensure_fcTL_is_valid(png_structp png_ptr,
+    png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den,
+    png_byte dispose_op, png_byte blend_op)
+{
+    if (width == 0 || width > PNG_UINT_31_MAX)
+        png_error(png_ptr, "invalid width in fcTL (0 or > 2^31-1)");
+    if (height == 0 || height > PNG_UINT_31_MAX)
+        png_error(png_ptr, "invalid height in fcTL (0 or > 2^31-1)");
+    if (x_offset > PNG_UINT_31_MAX)
+        png_error(png_ptr, "invalid x_offset in fcTL (> 2^31-1)");
+    if (y_offset > PNG_UINT_31_MAX)
+        png_error(png_ptr, "invalid y_offset in fcTL (> 2^31-1)");
+    if (width + x_offset > png_ptr->first_frame_width ||
+        height + y_offset > png_ptr->first_frame_height)
+        png_error(png_ptr, "dimensions of a frame are greater than "
+                           "the ones in IHDR");
+
+    if (dispose_op != PNG_DISPOSE_OP_NONE &&
+        dispose_op != PNG_DISPOSE_OP_BACKGROUND &&
+        dispose_op != PNG_DISPOSE_OP_PREVIOUS)
+        png_error(png_ptr, "invalid dispose_op in fcTL");
+
+    if (blend_op != PNG_BLEND_OP_SOURCE &&
+        blend_op != PNG_BLEND_OP_OVER)
+        png_error(png_ptr, "invalid blend_op in fcTL");
+
+    PNG_UNUSED(delay_num)
+    PNG_UNUSED(delay_den)
+}
+
+png_uint_32 PNGAPI
+png_set_first_frame_is_hidden(png_structp png_ptr, png_infop info_ptr,
+                              png_byte is_hidden)
+{
+    png_debug(1, "in png_first_frame_is_hidden()");
+
+    if (png_ptr == NULL)
+        return 0;
+
+    if (is_hidden != 0)
+        png_ptr->apng_flags |= PNG_FIRST_FRAME_HIDDEN;
+    else
+        png_ptr->apng_flags &= ~PNG_FIRST_FRAME_HIDDEN;
+
+    PNG_UNUSED(info_ptr)
+
+    return 1;
+}
+#endif /* APNG */
+
 #ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
 static png_byte
 check_location(png_const_structrp png_ptr, int location)
 {
diff --git a/pngstruct.h b/pngstruct.h
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -402,8 +402,29 @@ struct png_struct_def
 #ifdef PNG_MNG_FEATURES_SUPPORTED
    png_byte filter_type;
 #endif
 
+#ifdef PNG_APNG_SUPPORTED
+   png_uint_32 apng_flags;
+   png_uint_32 next_seq_num;         /* next fcTL/fdAT chunk sequence number */
+   png_uint_32 first_frame_width;
+   png_uint_32 first_frame_height;
+
+#ifdef PNG_READ_APNG_SUPPORTED
+   png_uint_32 num_frames_read;      /* incremented after all image data of */
+                                     /* a frame is read */
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+   png_progressive_frame_ptr frame_info_fn; /* frame info read callback */
+   png_progressive_frame_ptr frame_end_fn;  /* frame data read callback */
+#endif
+#endif
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   png_uint_32 num_frames_to_write;
+   png_uint_32 num_frames_written;
+#endif
+#endif /* APNG */
+
 /* New members added in libpng-1.2.0 */
 
 /* New members added in libpng-1.0.2 but first enabled by default in 1.2.0 */
 #ifdef PNG_USER_MEM_SUPPORTED
diff --git a/pngwrite.c b/pngwrite.c
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -127,8 +127,12 @@ png_write_info_before_PLTE(png_structrp 
        * an error and calls png_error while the color space is being set, yet
        * the application continues writing the PNG.  So check the 'invalid'
        * flag here too.
        */
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   if ((info_ptr->valid & PNG_INFO_acTL) != 0)
+      png_write_acTL(png_ptr, info_ptr->num_frames, info_ptr->num_plays);
+#endif
 #ifdef PNG_GAMMA_SUPPORTED
 #  ifdef PNG_WRITE_gAMA_SUPPORTED
       if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) == 0 &&
           (info_ptr->colorspace.flags & PNG_COLORSPACE_FROM_gAMA) != 0 &&
@@ -364,8 +368,13 @@ png_write_end(png_structrp png_ptr, png_
 
    if ((png_ptr->mode & PNG_HAVE_IDAT) == 0)
       png_error(png_ptr, "No IDATs written into file");
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   if (png_ptr->num_frames_written != png_ptr->num_frames_to_write)
+      png_error(png_ptr, "Not enough frames written");
+#endif
+
 #ifdef PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED
    if (png_ptr->num_palette_max > png_ptr->num_palette)
       png_benign_error(png_ptr, "Wrote palette index exceeding num_palette");
 #endif
@@ -2391,5 +2400,43 @@ png_image_write_to_file(png_imagep image
       return 0;
 }
 #endif /* SIMPLIFIED_WRITE_STDIO */
 #endif /* SIMPLIFIED_WRITE */
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+void PNGAPI
+png_write_frame_head(png_structp png_ptr, png_infop info_ptr,
+    png_bytepp row_pointers, png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den, png_byte dispose_op,
+    png_byte blend_op)
+{
+    png_debug(1, "in png_write_frame_head");
+
+    /* there is a chance this has been set after png_write_info was called,
+    * so it would be set but not written. is there a way to be sure? */
+    if ((info_ptr->valid & PNG_INFO_acTL) == 0)
+        png_error(png_ptr, "png_write_frame_head(): acTL not set");
+
+    png_write_reset(png_ptr);
+
+    png_write_reinit(png_ptr, info_ptr, width, height);
+
+    if ((png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN) == 0 ||
+        png_ptr->num_frames_written != 0)
+        png_write_fcTL(png_ptr, width, height, x_offset, y_offset,
+                       delay_num, delay_den, dispose_op, blend_op);
+
+    PNG_UNUSED(row_pointers)
+}
+
+void PNGAPI
+png_write_frame_tail(png_structp png_ptr, png_infop info_ptr)
+{
+    png_debug(1, "in png_write_frame_tail");
+
+    png_ptr->num_frames_written++;
+
+    PNG_UNUSED(info_ptr)
+}
+#endif /* WRITE_APNG */
 #endif /* WRITE */
diff --git a/pngwutil.c b/pngwutil.c
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -820,8 +820,13 @@ png_write_IHDR(png_structrp png_ptr, png
 
    /* Write the chunk */
    png_write_complete_chunk(png_ptr, png_IHDR, buf, 13);
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   png_ptr->first_frame_width = width;
+   png_ptr->first_frame_height = height;
+#endif
+
    if ((png_ptr->do_filter) == PNG_NO_FILTERS)
    {
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
           png_ptr->bit_depth < 8)
@@ -1002,9 +1007,19 @@ png_compress_IDAT(png_structrp png_ptr, 
                optimize_cmf(data, png_image_size(png_ptr));
 #endif
 
          if (size > 0)
+#ifdef PNG_WRITE_APNG_SUPPORTED
+         {
+            if (png_ptr->num_frames_written == 0)
+#endif
             png_write_complete_chunk(png_ptr, png_IDAT, data, size);
+#ifdef PNG_WRITE_APNG_SUPPORTED
+            else
+               png_write_fdAT(png_ptr, data, size);
+         }
+#endif /* WRITE_APNG */
+
          png_ptr->mode |= PNG_HAVE_IDAT;
 
          png_ptr->zstream.next_out = data;
          png_ptr->zstream.avail_out = size;
@@ -1049,9 +1064,19 @@ png_compress_IDAT(png_structrp png_ptr, 
             optimize_cmf(data, png_image_size(png_ptr));
 #endif
 
          if (size > 0)
+#ifdef PNG_WRITE_APNG_SUPPORTED
+         {
+            if (png_ptr->num_frames_written == 0)
+#endif
             png_write_complete_chunk(png_ptr, png_IDAT, data, size);
+#ifdef PNG_WRITE_APNG_SUPPORTED
+            else
+               png_write_fdAT(png_ptr, data, size);
+         }
+#endif /* WRITE_APNG */
+
          png_ptr->zstream.avail_out = 0;
          png_ptr->zstream.next_out = NULL;
          png_ptr->mode |= PNG_HAVE_IDAT | PNG_AFTER_IDAT;
 
@@ -1884,8 +1909,84 @@ png_write_tIME(png_structrp png_ptr, png
    png_write_complete_chunk(png_ptr, png_tIME, buf, 7);
 }
 #endif
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+void /* PRIVATE */
+png_write_acTL(png_structp png_ptr,
+    png_uint_32 num_frames, png_uint_32 num_plays)
+{
+    png_byte buf[8];
+
+    png_debug(1, "in png_write_acTL");
+
+    png_ptr->num_frames_to_write = num_frames;
+
+    if ((png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN) != 0)
+        num_frames--;
+
+    png_save_uint_32(buf, num_frames);
+    png_save_uint_32(buf + 4, num_plays);
+
+    png_write_complete_chunk(png_ptr, png_acTL, buf, (png_size_t)8);
+}
+
+void /* PRIVATE */
+png_write_fcTL(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den, png_byte dispose_op,
+    png_byte blend_op)
+{
+    png_byte buf[26];
+
+    png_debug(1, "in png_write_fcTL");
+
+    if (png_ptr->num_frames_written == 0 && (x_offset != 0 || y_offset != 0))
+        png_error(png_ptr, "x and/or y offset for the first frame aren't 0");
+    if (png_ptr->num_frames_written == 0 &&
+        (width != png_ptr->first_frame_width ||
+         height != png_ptr->first_frame_height))
+        png_error(png_ptr, "width and/or height in the first frame's fcTL "
+                           "don't match the ones in IHDR");
+
+    /* more error checking */
+    png_ensure_fcTL_is_valid(png_ptr, width, height, x_offset, y_offset,
+                             delay_num, delay_den, dispose_op, blend_op);
+
+    png_save_uint_32(buf, png_ptr->next_seq_num);
+    png_save_uint_32(buf + 4, width);
+    png_save_uint_32(buf + 8, height);
+    png_save_uint_32(buf + 12, x_offset);
+    png_save_uint_32(buf + 16, y_offset);
+    png_save_uint_16(buf + 20, delay_num);
+    png_save_uint_16(buf + 22, delay_den);
+    buf[24] = dispose_op;
+    buf[25] = blend_op;
+
+    png_write_complete_chunk(png_ptr, png_fcTL, buf, (png_size_t)26);
+
+    png_ptr->next_seq_num++;
+}
+
+void /* PRIVATE */
+png_write_fdAT(png_structp png_ptr,
+    png_const_bytep data, png_size_t length)
+{
+    png_byte buf[4];
+
+    png_write_chunk_header(png_ptr, png_fdAT, (png_uint_32)(4 + length));
+
+    png_save_uint_32(buf, png_ptr->next_seq_num);
+    png_write_chunk_data(png_ptr, buf, 4);
+
+    png_write_chunk_data(png_ptr, data, length);
+
+    png_write_chunk_end(png_ptr);
+
+    png_ptr->next_seq_num++;
+}
+#endif /* WRITE_APNG */
+
 /* Initializes the row writing capability of libpng */
 void /* PRIVATE */
 png_write_start_row(png_structrp png_ptr)
 {
@@ -2777,5 +2878,40 @@ png_write_filtered_row(png_structrp png_
       png_write_flush(png_ptr);
    }
 #endif /* WRITE_FLUSH */
 }
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+void /* PRIVATE */
+png_write_reset(png_structp png_ptr)
+{
+    png_ptr->row_number = 0;
+    png_ptr->pass = 0;
+    png_ptr->mode &= ~PNG_HAVE_IDAT;
+}
+
+void /* PRIVATE */
+png_write_reinit(png_structp png_ptr, png_infop info_ptr,
+                 png_uint_32 width, png_uint_32 height)
+{
+    if (png_ptr->num_frames_written == 0 &&
+        (width != png_ptr->first_frame_width ||
+         height != png_ptr->first_frame_height))
+        png_error(png_ptr, "width and/or height in the first frame's fcTL "
+                           "don't match the ones in IHDR");
+    if (width > png_ptr->first_frame_width ||
+        height > png_ptr->first_frame_height)
+        png_error(png_ptr, "width and/or height for a frame greater than "
+                           "the ones in IHDR");
+
+    png_set_IHDR(png_ptr, info_ptr, width, height,
+                 info_ptr->bit_depth, info_ptr->color_type,
+                 info_ptr->interlace_type, info_ptr->compression_type,
+                 info_ptr->filter_type);
+
+    png_ptr->width = width;
+    png_ptr->height = height;
+    png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, width);
+    png_ptr->usr_width = png_ptr->width;
+}
+#endif /* WRITE_APNG */
 #endif /* WRITE */