avcodec/pngdec: Fix alpha detection with skip_frame
[ffmpeg.git] / libavcodec / pngdec.c
index 436e798..24318fb 100644 (file)
 
 //#define DEBUG
 
+#include "libavutil/avassert.h"
 #include "libavutil/bprint.h"
 #include "libavutil/imgutils.h"
+#include "libavutil/stereo3d.h"
+
 #include "avcodec.h"
 #include "bytestream.h"
 #include "internal.h"
+#include "apng.h"
 #include "png.h"
 #include "pngdsp.h"
 #include "thread.h"
 
-/* TODO:
- * - add 16 bit depth support
- */
-
 #include <zlib.h>
 
 typedef struct PNGDecContext {
@@ -41,11 +41,18 @@ typedef struct PNGDecContext {
     AVCodecContext *avctx;
 
     GetByteContext gb;
+    ThreadFrame previous_picture;
     ThreadFrame last_picture;
     ThreadFrame picture;
 
     int state;
     int width, height;
+    int cur_w, cur_h;
+    int last_w, last_h;
+    int x_offset, y_offset;
+    int last_x_offset, last_y_offset;
+    uint8_t dispose_op, blend_op;
+    uint8_t last_dispose_op;
     int bit_depth;
     int color_type;
     int compression_type;
@@ -54,14 +61,17 @@ typedef struct PNGDecContext {
     int channels;
     int bits_per_pixel;
     int bpp;
+    int has_trns;
+    uint8_t transparent_color_be[6];
 
     uint8_t *image_buf;
     int image_linesize;
     uint32_t palette[256];
     uint8_t *crow_buf;
     uint8_t *last_row;
-    int last_row_size;
+    unsigned int last_row_size;
     uint8_t *tmp_row;
+    unsigned int tmp_row_size;
     uint8_t *buffer;
     int buffer_size;
     int pass;
@@ -88,8 +98,8 @@ static const uint8_t png_pass_dsp_mask[NB_PASSES] = {
 };
 
 /* NOTE: we try to construct a good looking image at each pass. width
  is the original image width. We also do pixel format conversion at
  this stage */
* is the original image width. We also do pixel format conversion at
* this stage */
 static void png_put_interlaced_row(uint8_t *dst, int width,
                                    int bits_per_pixel, int pass,
                                    int color_type, const uint8_t *src)
@@ -160,7 +170,8 @@ static void png_put_interlaced_row(uint8_t *dst, int width,
     }
 }
 
-void ff_add_png_paeth_prediction(uint8_t *dst, uint8_t *src, uint8_t *top, int w, int bpp)
+void ff_add_png_paeth_prediction(uint8_t *dst, uint8_t *src, uint8_t *top,
+                                 int w, int bpp)
 {
     int i;
     for (i = 0; i < w; i++) {
@@ -187,30 +198,42 @@ void ff_add_png_paeth_prediction(uint8_t *dst, uint8_t *src, uint8_t *top, int w
     }
 }
 
-#define UNROLL1(bpp, op) {\
-                 r = dst[0];\
-    if(bpp >= 2) g = dst[1];\
-    if(bpp >= 3) b = dst[2];\
-    if(bpp >= 4) a = dst[3];\
-    for(; i <= size - bpp; i+=bpp) {\
-        dst[i+0] = r = op(r, src[i+0], last[i+0]);\
-        if(bpp == 1) continue;\
-        dst[i+1] = g = op(g, src[i+1], last[i+1]);\
-        if(bpp == 2) continue;\
-        dst[i+2] = b = op(b, src[i+2], last[i+2]);\
-        if(bpp == 3) continue;\
-        dst[i+3] = a = op(a, src[i+3], last[i+3]);\
-    }\
-}
+#define UNROLL1(bpp, op)                                                      \
+    {                                                                         \
+        r = dst[0];                                                           \
+        if (bpp >= 2)                                                         \
+            g = dst[1];                                                       \
+        if (bpp >= 3)                                                         \
+            b = dst[2];                                                       \
+        if (bpp >= 4)                                                         \
+            a = dst[3];                                                       \
+        for (; i <= size - bpp; i += bpp) {                                   \
+            dst[i + 0] = r = op(r, src[i + 0], last[i + 0]);                  \
+            if (bpp == 1)                                                     \
+                continue;                                                     \
+            dst[i + 1] = g = op(g, src[i + 1], last[i + 1]);                  \
+            if (bpp == 2)                                                     \
+                continue;                                                     \
+            dst[i + 2] = b = op(b, src[i + 2], last[i + 2]);                  \
+            if (bpp == 3)                                                     \
+                continue;                                                     \
+            dst[i + 3] = a = op(a, src[i + 3], last[i + 3]);                  \
+        }                                                                     \
+    }
 
-#define UNROLL_FILTER(op)\
-         if(bpp == 1) UNROLL1(1, op)\
-    else if(bpp == 2) UNROLL1(2, op)\
-    else if(bpp == 3) UNROLL1(3, op)\
-    else if(bpp == 4) UNROLL1(4, op)\
-    for (; i < size; i++) {\
-        dst[i] = op(dst[i-bpp], src[i], last[i]);\
-    }\
+#define UNROLL_FILTER(op)                                                     \
+    if (bpp == 1) {                                                           \
+        UNROLL1(1, op)                                                        \
+    } else if (bpp == 2) {                                                    \
+        UNROLL1(2, op)                                                        \
+    } else if (bpp == 3) {                                                    \
+        UNROLL1(3, op)                                                        \
+    } else if (bpp == 4) {                                                    \
+        UNROLL1(4, op)                                                        \
+    }                                                                         \
+    for (; i < size; i++) {                                                   \
+        dst[i] = op(dst[i - bpp], src[i], last[i]);                           \
+    }
 
 /* NOTE: 'dst' can be equal to 'last' */
 static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
@@ -223,18 +246,17 @@ static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
         memcpy(dst, src, size);
         break;
     case PNG_FILTER_VALUE_SUB:
-        for (i = 0; i < bpp; i++) {
+        for (i = 0; i < bpp; i++)
             dst[i] = src[i];
-        }
         if (bpp == 4) {
-            p = *(int*)dst;
+            p = *(int *)dst;
             for (; i < size; i += bpp) {
-                int s = *(int*)(src + i);
+                unsigned s = *(int *)(src + i);
                 p = ((s & 0x7f7f7f7f) + (p & 0x7f7f7f7f)) ^ ((s ^ p) & 0x80808080);
-                *(int*)(dst + i) = p;
+                *(int *)(dst + i) = p;
             }
         } else {
-#define OP_SUB(x,s,l) x+s
+#define OP_SUB(x, s, l) ((x) + (s))
             UNROLL_FILTER(OP_SUB);
         }
         break;
@@ -243,22 +265,26 @@ static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
         break;
     case PNG_FILTER_VALUE_AVG:
         for (i = 0; i < bpp; i++) {
-            p = (last[i] >> 1);
+            p      = (last[i] >> 1);
             dst[i] = p + src[i];
         }
-#define OP_AVG(x,s,l) (((x + l) >> 1) + s) & 0xff
+#define OP_AVG(x, s, l) (((((x) + (l)) >> 1) + (s)) & 0xff)
         UNROLL_FILTER(OP_AVG);
         break;
     case PNG_FILTER_VALUE_PAETH:
         for (i = 0; i < bpp; i++) {
-            p = last[i];
+            p      = last[i];
             dst[i] = p + src[i];
         }
         if (bpp > 2 && size > 4) {
-            // would write off the end of the array if we let it process the last pixel with bpp=3
-            int w = bpp == 4 ? size : size - 3;
-            dsp->add_paeth_prediction(dst + i, src + i, last + i, w - i, bpp);
-            i = w;
+            /* would write off the end of the array if we let it process
+             * the last pixel with bpp=3 */
+            int w = (bpp & 3) ? size - 3 : size;
+
+            if (w > i) {
+                dsp->add_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
+                i = w;
+            }
         }
         ff_add_png_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
         break;
@@ -272,9 +298,9 @@ static void deloco_ ## NAME(TYPE *dst, int size, int alpha) \
 { \
     int i; \
     for (i = 0; i < size; i += 3 + alpha) { \
-        int g = dst [i+1]; \
-        dst[i+0] += g; \
-        dst[i+2] += g; \
+        int g = dst [i + 1]; \
+        dst[i + 0] += g; \
+        dst[i + 2] += g; \
     } \
 }
 
@@ -288,14 +314,14 @@ static void png_handle_row(PNGDecContext *s)
     int got_line;
 
     if (!s->interlace_type) {
-        ptr = s->image_buf + s->image_linesize * s->y;
-            if (s->y == 0)
-                last_row = s->last_row;
-            else
-                last_row = ptr - s->image_linesize;
+        ptr = s->image_buf + s->image_linesize * (s->y + s->y_offset) + s->x_offset * s->bpp;
+        if (s->y == 0)
+            last_row = s->last_row;
+        else
+            last_row = ptr - s->image_linesize;
 
-            png_filter_row(&s->dsp, ptr, s->crow_buf[0], s->crow_buf + 1,
-                           last_row, s->row_size, s->bpp);
+        png_filter_row(&s->dsp, ptr, s->crow_buf[0], s->crow_buf + 1,
+                       last_row, s->row_size, s->bpp);
         /* loco lags by 1 row so that it doesn't interfere with top prediction */
         if (s->filter_type == PNG_FILTER_TYPE_LOCO && s->y > 0) {
             if (s->bit_depth == 16) {
@@ -307,7 +333,7 @@ static void png_handle_row(PNGDecContext *s)
             }
         }
         s->y++;
-        if (s->y == s->height) {
+        if (s->y == s->cur_h) {
             s->state |= PNG_ALLIMAGE;
             if (s->filter_type == PNG_FILTER_TYPE_LOCO) {
                 if (s->bit_depth == 16) {
@@ -322,23 +348,24 @@ static void png_handle_row(PNGDecContext *s)
     } else {
         got_line = 0;
         for (;;) {
-            ptr = s->image_buf + s->image_linesize * s->y;
+            ptr = s->image_buf + s->image_linesize * (s->y + s->y_offset) + s->x_offset * s->bpp;
             if ((ff_png_pass_ymask[s->pass] << (s->y & 7)) & 0x80) {
                 /* if we already read one row, it is time to stop to
-                   wait for the next one */
+                 * wait for the next one */
                 if (got_line)
                     break;
                 png_filter_row(&s->dsp, s->tmp_row, s->crow_buf[0], s->crow_buf + 1,
                                s->last_row, s->pass_row_size, s->bpp);
-                FFSWAP(uint8_t*, s->last_row, s->tmp_row);
+                FFSWAP(uint8_t *, s->last_row, s->tmp_row);
+                FFSWAP(unsigned int, s->last_row_size, s->tmp_row_size);
                 got_line = 1;
             }
             if ((png_pass_dsp_ymask[s->pass] << (s->y & 7)) & 0x80) {
-                png_put_interlaced_row(ptr, s->width, s->bits_per_pixel, s->pass,
+                png_put_interlaced_row(ptr, s->cur_w, s->bits_per_pixel, s->pass,
                                        s->color_type, s->last_row);
             }
             s->y++;
-            if (s->y == s->height) {
+            if (s->y == s->cur_h) {
                 memset(s->last_row, 0, s->row_size);
                 for (;;) {
                     if (s->pass == NB_PASSES - 1) {
@@ -348,8 +375,8 @@ static void png_handle_row(PNGDecContext *s)
                         s->pass++;
                         s->y = 0;
                         s->pass_row_size = ff_png_pass_row_size(s->pass,
-                                                             s->bits_per_pixel,
-                                                             s->width);
+                                                                s->bits_per_pixel,
+                                                                s->cur_w);
                         s->crow_size = s->pass_row_size + 1;
                         if (s->pass_row_size != 0)
                             break;
@@ -358,7 +385,7 @@ static void png_handle_row(PNGDecContext *s)
                 }
             }
         }
-    the_end: ;
+the_end:;
     }
 }
 
@@ -383,6 +410,11 @@ static int png_decode_idat(PNGDecContext *s, int length)
             s->zstream.avail_out = s->crow_size;
             s->zstream.next_out  = s->crow_buf;
         }
+        if (ret == Z_STREAM_END && s->zstream.avail_in > 0) {
+            av_log(NULL, AV_LOG_WARNING,
+                   "%d undecompressed bytes left in buffer\n", s->zstream.avail_in);
+            return 0;
+        }
     }
     return 0;
 }
@@ -503,261 +535,278 @@ static int decode_text_chunk(PNGDecContext *s, uint32_t length, int compressed,
     return 0;
 }
 
-static int decode_frame(AVCodecContext *avctx,
-                        void *data, int *got_frame,
-                        AVPacket *avpkt)
+static int decode_ihdr_chunk(AVCodecContext *avctx, PNGDecContext *s,
+                             uint32_t length)
 {
-    PNGDecContext * const s = avctx->priv_data;
-    const uint8_t *buf      = avpkt->data;
-    int buf_size            = avpkt->size;
-    AVFrame *p;
-    AVDictionary *metadata  = NULL;
-    uint32_t tag, length;
-    int64_t sig;
-    int ret;
+    if (length != 13)
+        return AVERROR_INVALIDDATA;
 
-    ff_thread_release_buffer(avctx, &s->last_picture);
-    FFSWAP(ThreadFrame, s->picture, s->last_picture);
-    p = s->picture.f;
+    if (s->state & PNG_IDAT) {
+        av_log(avctx, AV_LOG_ERROR, "IHDR after IDAT\n");
+        return AVERROR_INVALIDDATA;
+    }
 
-    bytestream2_init(&s->gb, buf, buf_size);
+    if (s->state & PNG_IHDR) {
+        av_log(avctx, AV_LOG_ERROR, "Multiple IHDR\n");
+        return AVERROR_INVALIDDATA;
+    }
 
-    /* check signature */
-    sig = bytestream2_get_be64(&s->gb);
-    if (sig != PNGSIG &&
-        sig != MNGSIG) {
-        av_log(avctx, AV_LOG_ERROR, "Missing png signature\n");
+    s->width  = s->cur_w = bytestream2_get_be32(&s->gb);
+    s->height = s->cur_h = bytestream2_get_be32(&s->gb);
+    if (av_image_check_size(s->width, s->height, 0, avctx)) {
+        s->cur_w = s->cur_h = s->width = s->height = 0;
+        av_log(avctx, AV_LOG_ERROR, "Invalid image size\n");
         return AVERROR_INVALIDDATA;
     }
+    s->bit_depth        = bytestream2_get_byte(&s->gb);
+    s->color_type       = bytestream2_get_byte(&s->gb);
+    s->compression_type = bytestream2_get_byte(&s->gb);
+    s->filter_type      = bytestream2_get_byte(&s->gb);
+    s->interlace_type   = bytestream2_get_byte(&s->gb);
+    bytestream2_skip(&s->gb, 4); /* crc */
+    s->state |= PNG_IHDR;
+    if (avctx->debug & FF_DEBUG_PICT_INFO)
+        av_log(avctx, AV_LOG_DEBUG, "width=%d height=%d depth=%d color_type=%d "
+                "compression_type=%d filter_type=%d interlace_type=%d\n",
+                s->width, s->height, s->bit_depth, s->color_type,
+                s->compression_type, s->filter_type, s->interlace_type);
 
-    s->y = s->state = 0;
+    return 0;
+}
 
-    /* init the zlib */
-    s->zstream.zalloc = ff_png_zalloc;
-    s->zstream.zfree  = ff_png_zfree;
-    s->zstream.opaque = NULL;
-    ret = inflateInit(&s->zstream);
-    if (ret != Z_OK) {
-        av_log(avctx, AV_LOG_ERROR, "inflateInit returned error %d\n", ret);
-        return AVERROR_EXTERNAL;
+static int decode_phys_chunk(AVCodecContext *avctx, PNGDecContext *s)
+{
+    if (s->state & PNG_IDAT) {
+        av_log(avctx, AV_LOG_ERROR, "pHYs after IDAT\n");
+        return AVERROR_INVALIDDATA;
     }
-    for (;;) {
-        if (bytestream2_get_bytes_left(&s->gb) <= 0) {
-            av_log(avctx, AV_LOG_ERROR, "No bytes left\n");
-            goto fail;
-        }
+    avctx->sample_aspect_ratio.num = bytestream2_get_be32(&s->gb);
+    avctx->sample_aspect_ratio.den = bytestream2_get_be32(&s->gb);
+    if (avctx->sample_aspect_ratio.num < 0 || avctx->sample_aspect_ratio.den < 0)
+        avctx->sample_aspect_ratio = (AVRational){ 0, 1 };
+    bytestream2_skip(&s->gb, 1); /* unit specifier */
+    bytestream2_skip(&s->gb, 4); /* crc */
 
-        length = bytestream2_get_be32(&s->gb);
-        if (length > 0x7fffffff || length > bytestream2_get_bytes_left(&s->gb))  {
-            av_log(avctx, AV_LOG_ERROR, "chunk too big\n");
-            goto fail;
+    return 0;
+}
+
+static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
+                             uint32_t length, AVFrame *p)
+{
+    int ret;
+    size_t byte_depth = s->bit_depth > 8 ? 2 : 1;
+
+    if (!(s->state & PNG_IHDR)) {
+        av_log(avctx, AV_LOG_ERROR, "IDAT without IHDR\n");
+        return AVERROR_INVALIDDATA;
+    }
+    if (!(s->state & PNG_IDAT)) {
+        /* init image info */
+        avctx->width  = s->width;
+        avctx->height = s->height;
+
+        s->channels       = ff_png_get_nb_channels(s->color_type);
+        s->bits_per_pixel = s->bit_depth * s->channels;
+        s->bpp            = (s->bits_per_pixel + 7) >> 3;
+        s->row_size       = (s->cur_w * s->bits_per_pixel + 7) >> 3;
+
+        if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
+                s->color_type == PNG_COLOR_TYPE_RGB) {
+            avctx->pix_fmt = AV_PIX_FMT_RGB24;
+        } else if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
+                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
+            avctx->pix_fmt = AV_PIX_FMT_RGBA;
+        } else if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
+                s->color_type == PNG_COLOR_TYPE_GRAY) {
+            avctx->pix_fmt = AV_PIX_FMT_GRAY8;
+        } else if (s->bit_depth == 16 &&
+                s->color_type == PNG_COLOR_TYPE_GRAY) {
+            avctx->pix_fmt = AV_PIX_FMT_GRAY16BE;
+        } else if (s->bit_depth == 16 &&
+                s->color_type == PNG_COLOR_TYPE_RGB) {
+            avctx->pix_fmt = AV_PIX_FMT_RGB48BE;
+        } else if (s->bit_depth == 16 &&
+                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
+            avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
+        } else if ((s->bits_per_pixel == 1 || s->bits_per_pixel == 2 || s->bits_per_pixel == 4 || s->bits_per_pixel == 8) &&
+                s->color_type == PNG_COLOR_TYPE_PALETTE) {
+            avctx->pix_fmt = AV_PIX_FMT_PAL8;
+        } else if (s->bit_depth == 1 && s->bits_per_pixel == 1 && avctx->codec_id != AV_CODEC_ID_APNG) {
+            avctx->pix_fmt = AV_PIX_FMT_MONOBLACK;
+        } else if (s->bit_depth == 8 &&
+                s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
+            avctx->pix_fmt = AV_PIX_FMT_YA8;
+        } else if (s->bit_depth == 16 &&
+                s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
+            avctx->pix_fmt = AV_PIX_FMT_YA16BE;
+        } else {
+            av_log(avctx, AV_LOG_ERROR, "unsupported bit depth %d "
+                    "and color type %d\n",
+                    s->bit_depth, s->color_type);
+            return AVERROR_INVALIDDATA;
         }
-        tag = bytestream2_get_le32(&s->gb);
-        if (avctx->debug & FF_DEBUG_STARTCODE)
-            av_log(avctx, AV_LOG_DEBUG, "png: tag=%c%c%c%c length=%u\n",
-                (tag & 0xff),
-                ((tag >> 8) & 0xff),
-                ((tag >> 16) & 0xff),
-                ((tag >> 24) & 0xff), length);
-        switch (tag) {
-        case MKTAG('I', 'H', 'D', 'R'):
-            if (length != 13)
-                goto fail;
-            s->width  = bytestream2_get_be32(&s->gb);
-            s->height = bytestream2_get_be32(&s->gb);
-            if (av_image_check_size(s->width, s->height, 0, avctx)) {
-                s->width = s->height = 0;
-                av_log(avctx, AV_LOG_ERROR, "Invalid image size\n");
-                goto fail;
-            }
-            s->bit_depth        = bytestream2_get_byte(&s->gb);
-            s->color_type       = bytestream2_get_byte(&s->gb);
-            s->compression_type = bytestream2_get_byte(&s->gb);
-            s->filter_type      = bytestream2_get_byte(&s->gb);
-            s->interlace_type   = bytestream2_get_byte(&s->gb);
-            bytestream2_skip(&s->gb, 4); /* crc */
-            s->state |= PNG_IHDR;
-            if (avctx->debug & FF_DEBUG_PICT_INFO)
-                av_log(avctx, AV_LOG_DEBUG, "width=%d height=%d depth=%d color_type=%d "
-                    "compression_type=%d filter_type=%d interlace_type=%d\n",
-                    s->width, s->height, s->bit_depth, s->color_type,
-                    s->compression_type, s->filter_type, s->interlace_type);
-            break;
-        case MKTAG('p', 'H', 'Y', 's'):
-            if (s->state & PNG_IDAT) {
-                av_log(avctx, AV_LOG_ERROR, "pHYs after IDAT\n");
-                goto fail;
-            }
-            avctx->sample_aspect_ratio.num = bytestream2_get_be32(&s->gb);
-            avctx->sample_aspect_ratio.den = bytestream2_get_be32(&s->gb);
-            if (avctx->sample_aspect_ratio.num < 0 || avctx->sample_aspect_ratio.den < 0)
-                avctx->sample_aspect_ratio = (AVRational){ 0, 1 };
-            bytestream2_skip(&s->gb, 1); /* unit specifier */
-            bytestream2_skip(&s->gb, 4); /* crc */
-            break;
-        case MKTAG('I', 'D', 'A', 'T'):
-            if (!(s->state & PNG_IHDR)) {
-                av_log(avctx, AV_LOG_ERROR, "IDAT without IHDR\n");
-                goto fail;
+
+        if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE) {
+            switch (avctx->pix_fmt) {
+            case AV_PIX_FMT_RGB24:
+                avctx->pix_fmt = AV_PIX_FMT_RGBA;
+                break;
+
+            case AV_PIX_FMT_RGB48BE:
+                avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
+                break;
+
+            case AV_PIX_FMT_GRAY8:
+                avctx->pix_fmt = AV_PIX_FMT_YA8;
+                break;
+
+            case AV_PIX_FMT_GRAY16BE:
+                avctx->pix_fmt = AV_PIX_FMT_YA16BE;
+                break;
+
+            default:
+                avpriv_request_sample(avctx, "bit depth %d "
+                        "and color type %d with TRNS",
+                        s->bit_depth, s->color_type);
+                return AVERROR_INVALIDDATA;
             }
-            if (!(s->state & PNG_IDAT)) {
-                /* init image info */
-                avctx->width  = s->width;
-                avctx->height = s->height;
-
-                s->channels       = ff_png_get_nb_channels(s->color_type);
-                s->bits_per_pixel = s->bit_depth * s->channels;
-                s->bpp            = (s->bits_per_pixel + 7) >> 3;
-                s->row_size       = (avctx->width * s->bits_per_pixel + 7) >> 3;
-
-                if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
-                    s->color_type == PNG_COLOR_TYPE_RGB) {
-                    avctx->pix_fmt = AV_PIX_FMT_RGB24;
-                } else if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
-                           s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
-                    avctx->pix_fmt = AV_PIX_FMT_RGBA;
-                } else if ((s->bit_depth == 2 || s->bit_depth == 4 || s->bit_depth == 8) &&
-                           s->color_type == PNG_COLOR_TYPE_GRAY) {
-                    avctx->pix_fmt = AV_PIX_FMT_GRAY8;
-                } else if (s->bit_depth == 16 &&
-                           s->color_type == PNG_COLOR_TYPE_GRAY) {
-                    avctx->pix_fmt = AV_PIX_FMT_GRAY16BE;
-                } else if (s->bit_depth == 16 &&
-                           s->color_type == PNG_COLOR_TYPE_RGB) {
-                    avctx->pix_fmt = AV_PIX_FMT_RGB48BE;
-                } else if (s->bit_depth == 16 &&
-                           s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
-                    avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
-                } else if ((s->bits_per_pixel == 1 || s->bits_per_pixel == 2 || s->bits_per_pixel == 4 || s->bits_per_pixel == 8) &&
-                           s->color_type == PNG_COLOR_TYPE_PALETTE) {
-                    avctx->pix_fmt = AV_PIX_FMT_PAL8;
-                } else if (s->bit_depth == 1) {
-                    avctx->pix_fmt = AV_PIX_FMT_MONOBLACK;
-                } else if (s->bit_depth == 8 &&
-                           s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
-                    avctx->pix_fmt = AV_PIX_FMT_Y400A;
-                } else {
-                    av_log(avctx, AV_LOG_ERROR, "unsupported bit depth %d "
-                                                "and color type %d\n",
-                                                 s->bit_depth, s->color_type);
-                    goto fail;
-                }
 
-                if (ff_thread_get_buffer(avctx, &s->picture, AV_GET_BUFFER_FLAG_REF) < 0)
-                    goto fail;
-                ff_thread_finish_setup(avctx);
+            s->bpp += byte_depth;
+        }
 
-                p->pict_type        = AV_PICTURE_TYPE_I;
-                p->key_frame        = 1;
-                p->interlaced_frame = !!s->interlace_type;
+        if ((ret = ff_thread_get_buffer(avctx, &s->picture, AV_GET_BUFFER_FLAG_REF)) < 0)
+            return ret;
+        if (avctx->codec_id == AV_CODEC_ID_APNG && s->last_dispose_op != APNG_DISPOSE_OP_PREVIOUS) {
+            ff_thread_release_buffer(avctx, &s->previous_picture);
+            if ((ret = ff_thread_get_buffer(avctx, &s->previous_picture, AV_GET_BUFFER_FLAG_REF)) < 0)
+                return ret;
+        }
+        ff_thread_finish_setup(avctx);
 
-                /* compute the compressed row size */
-                if (!s->interlace_type) {
-                    s->crow_size = s->row_size + 1;
-                } else {
-                    s->pass = 0;
-                    s->pass_row_size = ff_png_pass_row_size(s->pass,
-                                                         s->bits_per_pixel,
-                                                         s->width);
-                    s->crow_size = s->pass_row_size + 1;
-                }
-                av_dlog(avctx, "row_size=%d crow_size =%d\n",
-                        s->row_size, s->crow_size);
-                s->image_buf      = p->data[0];
-                s->image_linesize = p->linesize[0];
-                /* copy the palette if needed */
-                if (avctx->pix_fmt == AV_PIX_FMT_PAL8)
-                    memcpy(p->data[1], s->palette, 256 * sizeof(uint32_t));
-                /* empty row is used if differencing to the first row */
-                av_fast_padded_mallocz(&s->last_row, &s->last_row_size, s->row_size);
-                if (!s->last_row)
-                    goto fail;
-                if (s->interlace_type ||
-                    s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
-                    s->tmp_row = av_malloc(s->row_size);
-                    if (!s->tmp_row)
-                        goto fail;
-                }
-                /* compressed row */
-                av_fast_padded_malloc(&s->buffer, &s->buffer_size, s->row_size + 16);
-                if (!s->buffer)
-                    goto fail;
-
-                /* we want crow_buf+1 to be 16-byte aligned */
-                s->crow_buf          = s->buffer + 15;
-                s->zstream.avail_out = s->crow_size;
-                s->zstream.next_out  = s->crow_buf;
-            }
-            s->state |= PNG_IDAT;
-            if (png_decode_idat(s, length) < 0)
-                goto fail;
-            bytestream2_skip(&s->gb, 4); /* crc */
-            break;
-        case MKTAG('P', 'L', 'T', 'E'):
-            {
-                int n, i, r, g, b;
-
-                if ((length % 3) != 0 || length > 256 * 3)
-                    goto skip_tag;
-                /* read the palette */
-                n = length / 3;
-                for (i = 0; i < n; i++) {
-                    r = bytestream2_get_byte(&s->gb);
-                    g = bytestream2_get_byte(&s->gb);
-                    b = bytestream2_get_byte(&s->gb);
-                    s->palette[i] = (0xFFU << 24) | (r << 16) | (g << 8) | b;
-                }
-                for (; i < 256; i++) {
-                    s->palette[i] = (0xFFU << 24);
-                }
-                s->state |= PNG_PLTE;
-                bytestream2_skip(&s->gb, 4); /* crc */
-            }
-            break;
-        case MKTAG('t', 'R', 'N', 'S'):
-            {
-                int v, i;
-
-                /* read the transparency. XXX: Only palette mode supported */
-                if (s->color_type != PNG_COLOR_TYPE_PALETTE ||
-                    length > 256 ||
-                    !(s->state & PNG_PLTE))
-                    goto skip_tag;
-                for (i = 0; i < length; i++) {
-                    v = bytestream2_get_byte(&s->gb);
-                    s->palette[i] = (s->palette[i] & 0x00ffffff) | (v << 24);
-                }
-                bytestream2_skip(&s->gb, 4); /* crc */
-            }
-            break;
-        case MKTAG('t', 'E', 'X', 't'):
-            if (decode_text_chunk(s, length, 0, &metadata) < 0)
-                av_log(avctx, AV_LOG_WARNING, "Broken tEXt chunk\n");
-            bytestream2_skip(&s->gb, length + 4);
-            break;
-        case MKTAG('z', 'T', 'X', 't'):
-            if (decode_text_chunk(s, length, 1, &metadata) < 0)
-                av_log(avctx, AV_LOG_WARNING, "Broken zTXt chunk\n");
-            bytestream2_skip(&s->gb, length + 4);
-            break;
-        case MKTAG('I', 'E', 'N', 'D'):
-            if (!(s->state & PNG_ALLIMAGE))
-                av_log(avctx, AV_LOG_ERROR, "IEND without all image\n");
-            if (!(s->state & (PNG_ALLIMAGE|PNG_IDAT))) {
-                goto fail;
-            }
-            bytestream2_skip(&s->gb, 4); /* crc */
-            goto exit_loop;
-        default:
-            /* skip tag */
-        skip_tag:
-            bytestream2_skip(&s->gb, length + 4);
-            break;
+        p->pict_type        = AV_PICTURE_TYPE_I;
+        p->key_frame        = 1;
+        p->interlaced_frame = !!s->interlace_type;
+
+        /* compute the compressed row size */
+        if (!s->interlace_type) {
+            s->crow_size = s->row_size + 1;
+        } else {
+            s->pass          = 0;
+            s->pass_row_size = ff_png_pass_row_size(s->pass,
+                    s->bits_per_pixel,
+                    s->cur_w);
+            s->crow_size = s->pass_row_size + 1;
+        }
+        ff_dlog(avctx, "row_size=%d crow_size =%d\n",
+                s->row_size, s->crow_size);
+        s->image_buf      = p->data[0];
+        s->image_linesize = p->linesize[0];
+        /* copy the palette if needed */
+        if (avctx->pix_fmt == AV_PIX_FMT_PAL8)
+            memcpy(p->data[1], s->palette, 256 * sizeof(uint32_t));
+        /* empty row is used if differencing to the first row */
+        av_fast_padded_mallocz(&s->last_row, &s->last_row_size, s->row_size);
+        if (!s->last_row)
+            return AVERROR_INVALIDDATA;
+        if (s->interlace_type ||
+                s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
+            av_fast_padded_malloc(&s->tmp_row, &s->tmp_row_size, s->row_size);
+            if (!s->tmp_row)
+                return AVERROR_INVALIDDATA;
         }
+        /* compressed row */
+        av_fast_padded_malloc(&s->buffer, &s->buffer_size, s->row_size + 16);
+        if (!s->buffer)
+            return AVERROR(ENOMEM);
+
+        /* we want crow_buf+1 to be 16-byte aligned */
+        s->crow_buf          = s->buffer + 15;
+        s->zstream.avail_out = s->crow_size;
+        s->zstream.next_out  = s->crow_buf;
     }
- exit_loop:
 
-    if (s->bits_per_pixel == 1 && s->color_type == PNG_COLOR_TYPE_PALETTE){
+    s->state |= PNG_IDAT;
+
+    /* set image to non-transparent bpp while decompressing */
+    if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE)
+        s->bpp -= byte_depth;
+
+    ret = png_decode_idat(s, length);
+
+    if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE)
+        s->bpp += byte_depth;
+
+    if (ret < 0)
+        return ret;
+
+    bytestream2_skip(&s->gb, 4); /* crc */
+
+    return 0;
+}
+
+static int decode_plte_chunk(AVCodecContext *avctx, PNGDecContext *s,
+                             uint32_t length)
+{
+    int n, i, r, g, b;
+
+    if ((length % 3) != 0 || length > 256 * 3)
+        return AVERROR_INVALIDDATA;
+    /* read the palette */
+    n = length / 3;
+    for (i = 0; i < n; i++) {
+        r = bytestream2_get_byte(&s->gb);
+        g = bytestream2_get_byte(&s->gb);
+        b = bytestream2_get_byte(&s->gb);
+        s->palette[i] = (0xFFU << 24) | (r << 16) | (g << 8) | b;
+    }
+    for (; i < 256; i++)
+        s->palette[i] = (0xFFU << 24);
+    s->state |= PNG_PLTE;
+    bytestream2_skip(&s->gb, 4);     /* crc */
+
+    return 0;
+}
+
+static int decode_trns_chunk(AVCodecContext *avctx, PNGDecContext *s,
+                             uint32_t length)
+{
+    int v, i;
+
+    if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
+        if (length > 256 || !(s->state & PNG_PLTE))
+            return AVERROR_INVALIDDATA;
+
+        for (i = 0; i < length; i++) {
+            v = bytestream2_get_byte(&s->gb);
+            s->palette[i] = (s->palette[i] & 0x00ffffff) | (v << 24);
+        }
+    } else if (s->color_type == PNG_COLOR_TYPE_GRAY || s->color_type == PNG_COLOR_TYPE_RGB) {
+        if ((s->color_type == PNG_COLOR_TYPE_GRAY && length != 2) ||
+            (s->color_type == PNG_COLOR_TYPE_RGB && length != 6))
+            return AVERROR_INVALIDDATA;
+
+        for (i = 0; i < length / 2; i++) {
+            /* only use the least significant bits */
+            v = av_mod_uintp2(bytestream2_get_be16(&s->gb), s->bit_depth);
+
+            if (s->bit_depth > 8)
+                AV_WB16(&s->transparent_color_be[2 * i], v);
+            else
+                s->transparent_color_be[i] = v;
+        }
+    } else {
+        return AVERROR_INVALIDDATA;
+    }
+
+    bytestream2_skip(&s->gb, 4); /* crc */
+    s->has_trns = 1;
+
+    return 0;
+}
+
+static void handle_small_bpp(PNGDecContext *s, AVFrame *p)
+{
+    if (s->bits_per_pixel == 1 && s->color_type == PNG_COLOR_TYPE_PALETTE) {
         int i, j, k;
         uint8_t *pd = p->data[0];
         for (j = 0; j < s->height; j++) {
@@ -777,13 +826,12 @@ static int decode_frame(AVCodecContext *avctx,
             }
             pd += s->image_linesize;
         }
-    }
-    if (s->bits_per_pixel == 2){
+    } else if (s->bits_per_pixel == 2) {
         int i, j;
         uint8_t *pd = p->data[0];
         for (j = 0; j < s->height; j++) {
             i = s->width / 4;
-            if (s->color_type == PNG_COLOR_TYPE_PALETTE){
+            if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
                 if ((s->width&3) >= 3) pd[4*i + 2]= (pd[i] >> 2) & 3;
                 if ((s->width&3) >= 2) pd[4*i + 1]= (pd[i] >> 4) & 3;
                 if ((s->width&3) >= 1) pd[4*i + 0]=  pd[i] >> 6;
@@ -806,18 +854,17 @@ static int decode_frame(AVCodecContext *avctx,
             }
             pd += s->image_linesize;
         }
-    }
-    if (s->bits_per_pixel == 4){
+    } else if (s->bits_per_pixel == 4) {
         int i, j;
         uint8_t *pd = p->data[0];
         for (j = 0; j < s->height; j++) {
             i = s->width/2;
-            if (s->color_type == PNG_COLOR_TYPE_PALETTE){
+            if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
                 if (s->width&1) pd[2*i+0]= pd[i]>>4;
                 for (i--; i >= 0; i--) {
-                pd[2*i + 1] = pd[i] & 15;
-                pd[2*i + 0] = pd[i] >> 4;
-            }
+                    pd[2*i + 1] = pd[i] & 15;
+                    pd[2*i + 0] = pd[i] >> 4;
+                }
             } else {
                 if (s->width & 1) pd[2*i + 0]= (pd[i] >> 4) * 0x11;
                 for (i--; i >= 0; i--) {
@@ -828,32 +875,464 @@ static int decode_frame(AVCodecContext *avctx,
             pd += s->image_linesize;
         }
     }
+}
+
+static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
+                             uint32_t length)
+{
+    uint32_t sequence_number;
+    int cur_w, cur_h, x_offset, y_offset, dispose_op, blend_op;
+
+    if (length != 26)
+        return AVERROR_INVALIDDATA;
+
+    if (!(s->state & PNG_IHDR)) {
+        av_log(avctx, AV_LOG_ERROR, "fctl before IHDR\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    s->last_w = s->cur_w;
+    s->last_h = s->cur_h;
+    s->last_x_offset = s->x_offset;
+    s->last_y_offset = s->y_offset;
+    s->last_dispose_op = s->dispose_op;
+
+    sequence_number = bytestream2_get_be32(&s->gb);
+    cur_w           = bytestream2_get_be32(&s->gb);
+    cur_h           = bytestream2_get_be32(&s->gb);
+    x_offset        = bytestream2_get_be32(&s->gb);
+    y_offset        = bytestream2_get_be32(&s->gb);
+    bytestream2_skip(&s->gb, 4); /* delay_num (2), delay_den (2) */
+    dispose_op      = bytestream2_get_byte(&s->gb);
+    blend_op        = bytestream2_get_byte(&s->gb);
+    bytestream2_skip(&s->gb, 4); /* crc */
+
+    if (sequence_number == 0 &&
+        (cur_w != s->width ||
+         cur_h != s->height ||
+         x_offset != 0 ||
+         y_offset != 0) ||
+        cur_w <= 0 || cur_h <= 0 ||
+        x_offset < 0 || y_offset < 0 ||
+        cur_w > s->width - x_offset|| cur_h > s->height - y_offset)
+            return AVERROR_INVALIDDATA;
+
+    if (blend_op != APNG_BLEND_OP_OVER && blend_op != APNG_BLEND_OP_SOURCE) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid blend_op %d\n", blend_op);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if (sequence_number == 0 && dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
+        // No previous frame to revert to for the first frame
+        // Spec says to just treat it as a APNG_DISPOSE_OP_BACKGROUND
+        dispose_op = APNG_DISPOSE_OP_BACKGROUND;
+    }
+
+    if (blend_op == APNG_BLEND_OP_OVER && !s->has_trns && (
+            avctx->pix_fmt == AV_PIX_FMT_RGB24 ||
+            avctx->pix_fmt == AV_PIX_FMT_RGB48BE ||
+            avctx->pix_fmt == AV_PIX_FMT_PAL8 ||
+            avctx->pix_fmt == AV_PIX_FMT_GRAY8 ||
+            avctx->pix_fmt == AV_PIX_FMT_GRAY16BE ||
+            avctx->pix_fmt == AV_PIX_FMT_MONOBLACK
+        )) {
+        // APNG_BLEND_OP_OVER is the same as APNG_BLEND_OP_SOURCE when there is no alpha channel
+        blend_op = APNG_BLEND_OP_SOURCE;
+    }
+
+    s->cur_w      = cur_w;
+    s->cur_h      = cur_h;
+    s->x_offset   = x_offset;
+    s->y_offset   = y_offset;
+    s->dispose_op = dispose_op;
+    s->blend_op   = blend_op;
+
+    return 0;
+}
+
+static void handle_p_frame_png(PNGDecContext *s, AVFrame *p)
+{
+    int i, j;
+    uint8_t *pd      = p->data[0];
+    uint8_t *pd_last = s->last_picture.f->data[0];
+    int ls = FFMIN(av_image_get_linesize(p->format, s->width, 0), s->width * s->bpp);
+
+    ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
+    for (j = 0; j < s->height; j++) {
+        for (i = 0; i < ls; i++)
+            pd[i] += pd_last[i];
+        pd      += s->image_linesize;
+        pd_last += s->image_linesize;
+    }
+}
+
+// divide by 255 and round to nearest
+// apply a fast variant: (X+127)/255 = ((X+127)*257+257)>>16 = ((X+128)*257)>>16
+#define FAST_DIV255(x) ((((x) + 128) * 257) >> 16)
+
+static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
+                               AVFrame *p)
+{
+    size_t x, y;
+    uint8_t *buffer;
+
+    if (s->blend_op == APNG_BLEND_OP_OVER &&
+        avctx->pix_fmt != AV_PIX_FMT_RGBA &&
+        avctx->pix_fmt != AV_PIX_FMT_GRAY8A &&
+        avctx->pix_fmt != AV_PIX_FMT_PAL8) {
+        avpriv_request_sample(avctx, "Blending with pixel format %s",
+                              av_get_pix_fmt_name(avctx->pix_fmt));
+        return AVERROR_PATCHWELCOME;
+    }
 
-     /* handle p-frames only if a predecessor frame is available */
-     if (s->last_picture.f->data[0]) {
-         if (   !(avpkt->flags & AV_PKT_FLAG_KEY) && avctx->codec_tag != AV_RL32("MPNG")
+    buffer = av_malloc_array(s->image_linesize, s->height);
+    if (!buffer)
+        return AVERROR(ENOMEM);
+
+
+    // Do the disposal operation specified by the last frame on the frame
+    if (s->last_dispose_op != APNG_DISPOSE_OP_PREVIOUS) {
+        ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
+        memcpy(buffer, s->last_picture.f->data[0], s->image_linesize * s->height);
+
+        if (s->last_dispose_op == APNG_DISPOSE_OP_BACKGROUND)
+            for (y = s->last_y_offset; y < s->last_y_offset + s->last_h; ++y)
+                memset(buffer + s->image_linesize * y + s->bpp * s->last_x_offset, 0, s->bpp * s->last_w);
+
+        memcpy(s->previous_picture.f->data[0], buffer, s->image_linesize * s->height);
+        ff_thread_report_progress(&s->previous_picture, INT_MAX, 0);
+    } else {
+        ff_thread_await_progress(&s->previous_picture, INT_MAX, 0);
+        memcpy(buffer, s->previous_picture.f->data[0], s->image_linesize * s->height);
+    }
+
+    // Perform blending
+    if (s->blend_op == APNG_BLEND_OP_SOURCE) {
+        for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) {
+            size_t row_start = s->image_linesize * y + s->bpp * s->x_offset;
+            memcpy(buffer + row_start, p->data[0] + row_start, s->bpp * s->cur_w);
+        }
+    } else { // APNG_BLEND_OP_OVER
+        for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) {
+            uint8_t *foreground = p->data[0] + s->image_linesize * y + s->bpp * s->x_offset;
+            uint8_t *background = buffer + s->image_linesize * y + s->bpp * s->x_offset;
+            for (x = s->x_offset; x < s->x_offset + s->cur_w; ++x, foreground += s->bpp, background += s->bpp) {
+                size_t b;
+                uint8_t foreground_alpha, background_alpha, output_alpha;
+                uint8_t output[10];
+
+                // Since we might be blending alpha onto alpha, we use the following equations:
+                // output_alpha = foreground_alpha + (1 - foreground_alpha) * background_alpha
+                // output = (foreground_alpha * foreground + (1 - foreground_alpha) * background_alpha * background) / output_alpha
+
+                switch (avctx->pix_fmt) {
+                case AV_PIX_FMT_RGBA:
+                    foreground_alpha = foreground[3];
+                    background_alpha = background[3];
+                    break;
+
+                case AV_PIX_FMT_GRAY8A:
+                    foreground_alpha = foreground[1];
+                    background_alpha = background[1];
+                    break;
+
+                case AV_PIX_FMT_PAL8:
+                    foreground_alpha = s->palette[foreground[0]] >> 24;
+                    background_alpha = s->palette[background[0]] >> 24;
+                    break;
+                }
+
+                if (foreground_alpha == 0)
+                    continue;
+
+                if (foreground_alpha == 255) {
+                    memcpy(background, foreground, s->bpp);
+                    continue;
+                }
+
+                if (avctx->pix_fmt == AV_PIX_FMT_PAL8) {
+                    // TODO: Alpha blending with PAL8 will likely need the entire image converted over to RGBA first
+                    avpriv_request_sample(avctx, "Alpha blending palette samples");
+                    background[0] = foreground[0];
+                    continue;
+                }
+
+                output_alpha = foreground_alpha + FAST_DIV255((255 - foreground_alpha) * background_alpha);
+
+                av_assert0(s->bpp <= 10);
+
+                for (b = 0; b < s->bpp - 1; ++b) {
+                    if (output_alpha == 0) {
+                        output[b] = 0;
+                    } else if (background_alpha == 255) {
+                        output[b] = FAST_DIV255(foreground_alpha * foreground[b] + (255 - foreground_alpha) * background[b]);
+                    } else {
+                        output[b] = (255 * foreground_alpha * foreground[b] + (255 - foreground_alpha) * background_alpha * background[b]) / (255 * output_alpha);
+                    }
+                }
+                output[b] = output_alpha;
+                memcpy(background, output, s->bpp);
+            }
+        }
+    }
+
+    // Copy blended buffer into the frame and free
+    memcpy(p->data[0], buffer, s->image_linesize * s->height);
+    av_free(buffer);
+
+    return 0;
+}
+
+static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
+                               AVFrame *p, AVPacket *avpkt)
+{
+    AVDictionary *metadata  = NULL;
+    uint32_t tag, length;
+    int decode_next_dat = 0;
+    int ret;
+
+    for (;;) {
+        length = bytestream2_get_bytes_left(&s->gb);
+        if (length <= 0) {
+
+            if (avctx->codec_id == AV_CODEC_ID_PNG &&
+                avctx->skip_frame == AVDISCARD_ALL) {
+                av_frame_set_metadata(p, metadata);
+                return 0;
+            }
+
+            if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && length == 0) {
+                if (!(s->state & PNG_IDAT))
+                    return 0;
+                else
+                    goto exit_loop;
+            }
+            av_log(avctx, AV_LOG_ERROR, "%d bytes left\n", length);
+            if (   s->state & PNG_ALLIMAGE
+                && avctx->strict_std_compliance <= FF_COMPLIANCE_NORMAL)
+                goto exit_loop;
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
+
+        length = bytestream2_get_be32(&s->gb);
+        if (length > 0x7fffffff || length > bytestream2_get_bytes_left(&s->gb)) {
+            av_log(avctx, AV_LOG_ERROR, "chunk too big\n");
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
+        tag = bytestream2_get_le32(&s->gb);
+        if (avctx->debug & FF_DEBUG_STARTCODE)
+            av_log(avctx, AV_LOG_DEBUG, "png: tag=%c%c%c%c length=%u\n",
+                (tag & 0xff),
+                ((tag >> 8) & 0xff),
+                ((tag >> 16) & 0xff),
+                ((tag >> 24) & 0xff), length);
+
+        if (avctx->codec_id == AV_CODEC_ID_PNG &&
+            avctx->skip_frame == AVDISCARD_ALL) {
+            switch(tag) {
+            case MKTAG('I', 'H', 'D', 'R'):
+            case MKTAG('p', 'H', 'Y', 's'):
+            case MKTAG('t', 'E', 'X', 't'):
+            case MKTAG('I', 'D', 'A', 'T'):
+            case MKTAG('t', 'R', 'N', 'S'):
+                break;
+            default:
+                goto skip_tag;
+            }
+        }
+
+        switch (tag) {
+        case MKTAG('I', 'H', 'D', 'R'):
+            if ((ret = decode_ihdr_chunk(avctx, s, length)) < 0)
+                goto fail;
+            break;
+        case MKTAG('p', 'H', 'Y', 's'):
+            if ((ret = decode_phys_chunk(avctx, s)) < 0)
+                goto fail;
+            break;
+        case MKTAG('f', 'c', 'T', 'L'):
+            if (!CONFIG_APNG_DECODER || avctx->codec_id != AV_CODEC_ID_APNG)
+                goto skip_tag;
+            if ((ret = decode_fctl_chunk(avctx, s, length)) < 0)
+                goto fail;
+            decode_next_dat = 1;
+            break;
+        case MKTAG('f', 'd', 'A', 'T'):
+            if (!CONFIG_APNG_DECODER || avctx->codec_id != AV_CODEC_ID_APNG)
+                goto skip_tag;
+            if (!decode_next_dat) {
+                ret = AVERROR_INVALIDDATA;
+                goto fail;
+            }
+            bytestream2_get_be32(&s->gb);
+            length -= 4;
+            /* fallthrough */
+        case MKTAG('I', 'D', 'A', 'T'):
+            if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && !decode_next_dat)
+                goto skip_tag;
+            if ((ret = decode_idat_chunk(avctx, s, length, p)) < 0)
+                goto fail;
+            break;
+        case MKTAG('P', 'L', 'T', 'E'):
+            if (decode_plte_chunk(avctx, s, length) < 0)
+                goto skip_tag;
+            break;
+        case MKTAG('t', 'R', 'N', 'S'):
+            if (decode_trns_chunk(avctx, s, length) < 0)
+                goto skip_tag;
+            break;
+        case MKTAG('t', 'E', 'X', 't'):
+            if (decode_text_chunk(s, length, 0, &metadata) < 0)
+                av_log(avctx, AV_LOG_WARNING, "Broken tEXt chunk\n");
+            bytestream2_skip(&s->gb, length + 4);
+            break;
+        case MKTAG('z', 'T', 'X', 't'):
+            if (decode_text_chunk(s, length, 1, &metadata) < 0)
+                av_log(avctx, AV_LOG_WARNING, "Broken zTXt chunk\n");
+            bytestream2_skip(&s->gb, length + 4);
+            break;
+        case MKTAG('s', 'T', 'E', 'R'): {
+            int mode = bytestream2_get_byte(&s->gb);
+            AVStereo3D *stereo3d = av_stereo3d_create_side_data(p);
+            if (!stereo3d)
+                goto fail;
+
+            if (mode == 0 || mode == 1) {
+                stereo3d->type  = AV_STEREO3D_SIDEBYSIDE;
+                stereo3d->flags = mode ? 0 : AV_STEREO3D_FLAG_INVERT;
+            } else {
+                 av_log(avctx, AV_LOG_WARNING,
+                        "Unknown value in sTER chunk (%d)\n", mode);
+            }
+            bytestream2_skip(&s->gb, 4); /* crc */
+            break;
+        }
+        case MKTAG('I', 'E', 'N', 'D'):
+            if (!(s->state & PNG_ALLIMAGE))
+                av_log(avctx, AV_LOG_ERROR, "IEND without all image\n");
+            if (!(s->state & (PNG_ALLIMAGE|PNG_IDAT))) {
+                ret = AVERROR_INVALIDDATA;
+                goto fail;
+            }
+            bytestream2_skip(&s->gb, 4); /* crc */
+            goto exit_loop;
+        default:
+            /* skip tag */
+skip_tag:
+            bytestream2_skip(&s->gb, length + 4);
+            break;
+        }
+    }
+exit_loop:
+    if (avctx->codec_id == AV_CODEC_ID_PNG &&
+        avctx->skip_frame == AVDISCARD_ALL) {
+        av_frame_set_metadata(p, metadata);
+        return 0;
+    }
+
+    if (s->bits_per_pixel <= 4)
+        handle_small_bpp(s, p);
+
+    /* apply transparency if needed */
+    if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE) {
+        size_t byte_depth = s->bit_depth > 8 ? 2 : 1;
+        size_t raw_bpp = s->bpp - byte_depth;
+        unsigned x, y;
+
+        for (y = 0; y < s->height; ++y) {
+            uint8_t *row = &s->image_buf[s->image_linesize * y];
+
+            /* since we're updating in-place, we have to go from right to left */
+            for (x = s->width; x > 0; --x) {
+                uint8_t *pixel = &row[s->bpp * (x - 1)];
+                memmove(pixel, &row[raw_bpp * (x - 1)], raw_bpp);
+
+                if (!memcmp(pixel, s->transparent_color_be, raw_bpp)) {
+                    memset(&pixel[raw_bpp], 0, byte_depth);
+                } else {
+                    memset(&pixel[raw_bpp], 0xff, byte_depth);
+                }
+            }
+        }
+    }
+
+    /* handle p-frames only if a predecessor frame is available */
+    if (s->last_picture.f->data[0]) {
+        if (   !(avpkt->flags & AV_PKT_FLAG_KEY) && avctx->codec_tag != AV_RL32("MPNG")
             && s->last_picture.f->width == p->width
             && s->last_picture.f->height== p->height
             && s->last_picture.f->format== p->format
          ) {
-            int i, j;
-            uint8_t *pd      = p->data[0];
-            uint8_t *pd_last = s->last_picture.f->data[0];
-
-            ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
-            for (j = 0; j < s->height; j++) {
-                for (i = 0; i < s->width * s->bpp; i++) {
-                    pd[i] += pd_last[i];
-                }
-                pd      += s->image_linesize;
-                pd_last += s->image_linesize;
-            }
+            if (CONFIG_PNG_DECODER && avctx->codec_id != AV_CODEC_ID_APNG)
+                handle_p_frame_png(s, p);
+            else if (CONFIG_APNG_DECODER &&
+                     avctx->codec_id == AV_CODEC_ID_APNG &&
+                     (ret = handle_p_frame_apng(avctx, s, p)) < 0)
+                goto fail;
         }
     }
     ff_thread_report_progress(&s->picture, INT_MAX, 0);
+    ff_thread_report_progress(&s->previous_picture, INT_MAX, 0);
 
     av_frame_set_metadata(p, metadata);
     metadata   = NULL;
+    return 0;
+
+fail:
+    av_dict_free(&metadata);
+    ff_thread_report_progress(&s->picture, INT_MAX, 0);
+    ff_thread_report_progress(&s->previous_picture, INT_MAX, 0);
+    return ret;
+}
+
+#if CONFIG_PNG_DECODER
+static int decode_frame_png(AVCodecContext *avctx,
+                        void *data, int *got_frame,
+                        AVPacket *avpkt)
+{
+    PNGDecContext *const s = avctx->priv_data;
+    const uint8_t *buf     = avpkt->data;
+    int buf_size           = avpkt->size;
+    AVFrame *p;
+    int64_t sig;
+    int ret;
+
+    ff_thread_release_buffer(avctx, &s->last_picture);
+    FFSWAP(ThreadFrame, s->picture, s->last_picture);
+    p = s->picture.f;
+
+    bytestream2_init(&s->gb, buf, buf_size);
+
+    /* check signature */
+    sig = bytestream2_get_be64(&s->gb);
+    if (sig != PNGSIG &&
+        sig != MNGSIG) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid PNG signature 0x%08"PRIX64".\n", sig);
+        return AVERROR_INVALIDDATA;
+    }
+
+    s->y = s->state = s->has_trns = 0;
+
+    /* init the zlib */
+    s->zstream.zalloc = ff_png_zalloc;
+    s->zstream.zfree  = ff_png_zfree;
+    s->zstream.opaque = NULL;
+    ret = inflateInit(&s->zstream);
+    if (ret != Z_OK) {
+        av_log(avctx, AV_LOG_ERROR, "inflateInit returned error %d\n", ret);
+        return AVERROR_EXTERNAL;
+    }
+
+    if ((ret = decode_frame_common(avctx, s, p, avpkt)) < 0)
+        goto the_end;
+
+    if (avctx->skip_frame == AVDISCARD_ALL) {
+        *got_frame = 0;
+        ret = bytestream2_tell(&s->gb);
+        goto the_end;
+    }
 
     if ((ret = av_frame_ref(data, s->picture.f)) < 0)
         return ret;
@@ -861,42 +1340,135 @@ static int decode_frame(AVCodecContext *avctx,
     *got_frame = 1;
 
     ret = bytestream2_tell(&s->gb);
- the_end:
+the_end:
     inflateEnd(&s->zstream);
     s->crow_buf = NULL;
-    av_freep(&s->tmp_row);
     return ret;
- fail:
-    av_dict_free(&metadata);
-    ff_thread_report_progress(&s->picture, INT_MAX, 0);
-    ret = AVERROR_INVALIDDATA;
-    goto the_end;
 }
+#endif
+
+#if CONFIG_APNG_DECODER
+static int decode_frame_apng(AVCodecContext *avctx,
+                        void *data, int *got_frame,
+                        AVPacket *avpkt)
+{
+    PNGDecContext *const s = avctx->priv_data;
+    int ret;
+    AVFrame *p;
+
+    ff_thread_release_buffer(avctx, &s->last_picture);
+    FFSWAP(ThreadFrame, s->picture, s->last_picture);
+    p = s->picture.f;
+
+    if (!(s->state & PNG_IHDR)) {
+        if (!avctx->extradata_size)
+            return AVERROR_INVALIDDATA;
+
+        /* only init fields, there is no zlib use in extradata */
+        s->zstream.zalloc = ff_png_zalloc;
+        s->zstream.zfree  = ff_png_zfree;
+
+        bytestream2_init(&s->gb, avctx->extradata, avctx->extradata_size);
+        if ((ret = decode_frame_common(avctx, s, p, avpkt)) < 0)
+            goto end;
+    }
+
+    /* reset state for a new frame */
+    if ((ret = inflateInit(&s->zstream)) != Z_OK) {
+        av_log(avctx, AV_LOG_ERROR, "inflateInit returned error %d\n", ret);
+        ret = AVERROR_EXTERNAL;
+        goto end;
+    }
+    s->y = 0;
+    s->state &= ~(PNG_IDAT | PNG_ALLIMAGE);
+    bytestream2_init(&s->gb, avpkt->data, avpkt->size);
+    if ((ret = decode_frame_common(avctx, s, p, avpkt)) < 0)
+        goto end;
+
+    if (!(s->state & PNG_ALLIMAGE))
+        av_log(avctx, AV_LOG_WARNING, "Frame did not contain a complete image\n");
+    if (!(s->state & (PNG_ALLIMAGE|PNG_IDAT))) {
+        ret = AVERROR_INVALIDDATA;
+        goto end;
+    }
+    if ((ret = av_frame_ref(data, s->picture.f)) < 0)
+        goto end;
+
+    *got_frame = 1;
+    ret = bytestream2_tell(&s->gb);
+
+end:
+    inflateEnd(&s->zstream);
+    return ret;
+}
+#endif
 
+#if HAVE_THREADS
 static int update_thread_context(AVCodecContext *dst, const AVCodecContext *src)
 {
     PNGDecContext *psrc = src->priv_data;
     PNGDecContext *pdst = dst->priv_data;
+    int ret;
 
     if (dst == src)
         return 0;
 
     ff_thread_release_buffer(dst, &pdst->picture);
-    if (psrc->picture.f->data[0])
-        return ff_thread_ref_frame(&pdst->picture, &psrc->picture);
+    if (psrc->picture.f->data[0] &&
+        (ret = ff_thread_ref_frame(&pdst->picture, &psrc->picture)) < 0)
+        return ret;
+    if (CONFIG_APNG_DECODER && dst->codec_id == AV_CODEC_ID_APNG) {
+        pdst->width             = psrc->width;
+        pdst->height            = psrc->height;
+        pdst->bit_depth         = psrc->bit_depth;
+        pdst->color_type        = psrc->color_type;
+        pdst->compression_type  = psrc->compression_type;
+        pdst->interlace_type    = psrc->interlace_type;
+        pdst->filter_type       = psrc->filter_type;
+        pdst->cur_w = psrc->cur_w;
+        pdst->cur_h = psrc->cur_h;
+        pdst->x_offset = psrc->x_offset;
+        pdst->y_offset = psrc->y_offset;
+        pdst->has_trns = psrc->has_trns;
+        memcpy(pdst->transparent_color_be, psrc->transparent_color_be, sizeof(pdst->transparent_color_be));
+
+        pdst->dispose_op = psrc->dispose_op;
+
+        memcpy(pdst->palette, psrc->palette, sizeof(pdst->palette));
+
+        pdst->state |= psrc->state & (PNG_IHDR | PNG_PLTE);
+
+        ff_thread_release_buffer(dst, &pdst->last_picture);
+        if (psrc->last_picture.f->data[0] &&
+            (ret = ff_thread_ref_frame(&pdst->last_picture, &psrc->last_picture)) < 0)
+            return ret;
+
+        ff_thread_release_buffer(dst, &pdst->previous_picture);
+        if (psrc->previous_picture.f->data[0] &&
+            (ret = ff_thread_ref_frame(&pdst->previous_picture, &psrc->previous_picture)) < 0)
+            return ret;
+    }
 
     return 0;
 }
+#endif
 
 static av_cold int png_dec_init(AVCodecContext *avctx)
 {
     PNGDecContext *s = avctx->priv_data;
 
+    avctx->color_range = AVCOL_RANGE_JPEG;
+
     s->avctx = avctx;
+    s->previous_picture.f = av_frame_alloc();
     s->last_picture.f = av_frame_alloc();
     s->picture.f = av_frame_alloc();
-    if (!s->last_picture.f || !s->picture.f)
+    if (!s->previous_picture.f || !s->last_picture.f || !s->picture.f) {
+        av_frame_free(&s->previous_picture.f);
+        av_frame_free(&s->last_picture.f);
+        av_frame_free(&s->picture.f);
         return AVERROR(ENOMEM);
+    }
 
     if (!avctx->internal->is_copy) {
         avctx->internal->allocate_progress = 1;
@@ -910,6 +1482,8 @@ static av_cold int png_dec_end(AVCodecContext *avctx)
 {
     PNGDecContext *s = avctx->priv_data;
 
+    ff_thread_release_buffer(avctx, &s->previous_picture);
+    av_frame_free(&s->previous_picture.f);
     ff_thread_release_buffer(avctx, &s->last_picture);
     av_frame_free(&s->last_picture.f);
     ff_thread_release_buffer(avctx, &s->picture);
@@ -918,20 +1492,41 @@ static av_cold int png_dec_end(AVCodecContext *avctx)
     s->buffer_size = 0;
     av_freep(&s->last_row);
     s->last_row_size = 0;
+    av_freep(&s->tmp_row);
+    s->tmp_row_size = 0;
 
     return 0;
 }
 
+#if CONFIG_APNG_DECODER
+AVCodec ff_apng_decoder = {
+    .name           = "apng",
+    .long_name      = NULL_IF_CONFIG_SMALL("APNG (Animated Portable Network Graphics) image"),
+    .type           = AVMEDIA_TYPE_VIDEO,
+    .id             = AV_CODEC_ID_APNG,
+    .priv_data_size = sizeof(PNGDecContext),
+    .init           = png_dec_init,
+    .close          = png_dec_end,
+    .decode         = decode_frame_apng,
+    .init_thread_copy = ONLY_IF_THREADS_ENABLED(png_dec_init),
+    .update_thread_context = ONLY_IF_THREADS_ENABLED(update_thread_context),
+    .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS /*| AV_CODEC_CAP_DRAW_HORIZ_BAND*/,
+};
+#endif
+
+#if CONFIG_PNG_DECODER
 AVCodec ff_png_decoder = {
     .name           = "png",
+    .long_name      = NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
     .type           = AVMEDIA_TYPE_VIDEO,
     .id             = AV_CODEC_ID_PNG,
     .priv_data_size = sizeof(PNGDecContext),
     .init           = png_dec_init,
     .close          = png_dec_end,
-    .decode         = decode_frame,
+    .decode         = decode_frame_png,
     .init_thread_copy = ONLY_IF_THREADS_ENABLED(png_dec_init),
     .update_thread_context = ONLY_IF_THREADS_ENABLED(update_thread_context),
-    .capabilities   = CODEC_CAP_DR1 | CODEC_CAP_FRAME_THREADS /*| CODEC_CAP_DRAW_HORIZ_BAND*/,
-    .long_name      = NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
+    .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS /*| AV_CODEC_CAP_DRAW_HORIZ_BAND*/,
+    .caps_internal  = FF_CODEC_CAP_SKIP_FRAME_FILL_PARAM,
 };
+#endif