avcodec/pngdec: Fix alpha detection with skip_frame
[ffmpeg.git] / libavcodec / pngdec.c
index 4c9d321..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"
-#include "libavformat/apng.h"
 
 #include <zlib.h>
 
@@ -38,14 +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;
@@ -54,6 +61,8 @@ 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;
@@ -270,9 +279,10 @@ static void png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
         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;
+            int w = (bpp & 3) ? size - 3 : size;
+
             if (w > i) {
-                dsp->add_paeth_prediction(dst + i, src + i, last + i, w - i, bpp);
+                dsp->add_paeth_prediction(dst + i, src + i, last + i, size - i, bpp);
                 i = w;
             }
         }
@@ -305,13 +315,13 @@ static void png_handle_row(PNGDecContext *s)
 
     if (!s->interlace_type) {
         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;
+        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) {
@@ -536,10 +546,15 @@ static int decode_ihdr_chunk(AVCodecContext *avctx, PNGDecContext *s,
         return AVERROR_INVALIDDATA;
     }
 
+    if (s->state & PNG_IHDR) {
+        av_log(avctx, AV_LOG_ERROR, "Multiple IHDR\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     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->width = s->height = 0;
+        s->cur_w = s->cur_h = s->width = s->height = 0;
         av_log(avctx, AV_LOG_ERROR, "Invalid image size\n");
         return AVERROR_INVALIDDATA;
     }
@@ -579,6 +594,7 @@ 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");
@@ -615,7 +631,7 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
         } 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) {
+        } 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) {
@@ -630,8 +646,41 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
             return AVERROR_INVALIDDATA;
         }
 
+        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;
+            }
+
+            s->bpp += byte_depth;
+        }
+
         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);
 
         p->pict_type        = AV_PICTURE_TYPE_I;
@@ -648,7 +697,7 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
                     s->cur_w);
             s->crow_size = s->pass_row_size + 1;
         }
-        av_dlog(avctx, "row_size=%d crow_size =%d\n",
+        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];
@@ -674,14 +723,22 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
         s->crow_buf          = s->buffer + 15;
         s->zstream.avail_out = s->crow_size;
         s->zstream.next_out  = s->crow_buf;
-
-        if (avctx->codec_id == AV_CODEC_ID_APNG &&
-            s->dispose_op == APNG_DISPOSE_OP_BACKGROUND)
-            memset(s->zstream.next_out, 0, s->zstream.avail_out);
     }
+
     s->state |= PNG_IDAT;
-    if ((ret = png_decode_idat(s, length)) < 0)
+
+    /* 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;
@@ -715,16 +772,34 @@ static int decode_trns_chunk(AVCodecContext *avctx, PNGDecContext *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))
+    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;
-    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 */
+
+    bytestream2_skip(&s->gb, 4); /* crc */
+    s->has_trns = 1;
 
     return 0;
 }
@@ -806,40 +881,72 @@ 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);
-    s->cur_w        = bytestream2_get_be32(&s->gb);
-    s->cur_h        = bytestream2_get_be32(&s->gb);
-    s->x_offset     = bytestream2_get_be32(&s->gb);
-    s->y_offset     = 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) */
-    s->dispose_op   = bytestream2_get_byte(&s->gb);
-    s->blend_op     = bytestream2_get_byte(&s->gb);
+    dispose_op      = bytestream2_get_byte(&s->gb);
+    blend_op        = bytestream2_get_byte(&s->gb);
     bytestream2_skip(&s->gb, 4); /* crc */
 
     if (sequence_number == 0 &&
-        (s->cur_w != s->width ||
-         s->cur_h != s->height ||
-         s->x_offset != 0 ||
-         s->y_offset != 0) ||
-        s->cur_w <= 0 || s->cur_h <= 0 ||
-        s->x_offset < 0 || s->y_offset < 0 ||
-        s->cur_w > s->width - s->x_offset|| s->cur_h > s->height - s->y_offset)
+        (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;
 
-    /* always (re)start with a clean frame */
-    if (sequence_number == 0)
-        s->dispose_op = APNG_DISPOSE_OP_BACKGROUND;
+    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 (s->dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
-        av_log(avctx, AV_LOG_ERROR,
-               "Dispose operation 'previous' is not yet implemented, using 'none'.\n");
-        s->dispose_op = APNG_DISPOSE_OP_NONE;
+    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;
 }
 
@@ -866,78 +973,112 @@ static void handle_p_frame_png(PNGDecContext *s, AVFrame *p)
 static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
                                AVFrame *p)
 {
-    int i, j;
-    uint8_t *pd      = p->data[0];
-    /* TODO make pd_last point to the one before for APNG_DISPOSE_OP_PREVIOUS */
-    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);
+    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_ARGB) {
+        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;
     }
 
-    ff_thread_await_progress(&s->last_picture, INT_MAX, 0);
-    for (j = 0; j < s->y_offset; j++) {
-        for (i = 0; i < ls; i++)
-            pd[i] = pd_last[i];
-        pd      += s->image_linesize;
-        pd_last += s->image_linesize;
-    }
+    buffer = av_malloc_array(s->image_linesize, s->height);
+    if (!buffer)
+        return AVERROR(ENOMEM);
 
-    if (s->blend_op == APNG_BLEND_OP_OVER) {
-        uint8_t ri, gi, bi, ai;
 
-        if (avctx->pix_fmt == AV_PIX_FMT_RGBA) {
-            ri = 0;
-            gi = 1;
-            bi = 2;
-            ai = 3;
-        } else {
-            ri = 3;
-            gi = 2;
-            bi = 1;
-            ai = 0;
-        }
+    // 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);
+    }
 
-        for (j = s->y_offset; j < s->y_offset + s->cur_h; j++) {
-            for (i = 0; i < s->x_offset * s->bpp; i++)
-                pd[i] = pd_last[i];
-            for (; i < (s->x_offset + s->cur_w) * s->bpp; i += s->bpp) {
-                uint8_t alpha = pd[i+ai];
-
-                /* output = alpha * foreground + (1-alpha) * background */
-                switch (alpha) {
-                case 0:
-                    pd[i+ri] = pd_last[i+ri];
-                    pd[i+gi] = pd_last[i+gi];
-                    pd[i+bi] = pd_last[i+bi];
-                    pd[i+ai] = 0xff;
+    // 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 255:
+
+                case AV_PIX_FMT_GRAY8A:
+                    foreground_alpha = foreground[1];
+                    background_alpha = background[1];
                     break;
-                default:
-                    pd[i+ri] = FAST_DIV255(alpha * pd[i+ri] + (255 - alpha) * pd_last[i+ri]);
-                    pd[i+gi] = FAST_DIV255(alpha * pd[i+gi] + (255 - alpha) * pd_last[i+gi]);
-                    pd[i+bi] = FAST_DIV255(alpha * pd[i+bi] + (255 - alpha) * pd_last[i+bi]);
-                    pd[i+ai] = 0xff;
+
+                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);
             }
-            for (; i < ls; i++)
-                pd[i] = pd_last[i];
-            pd      += s->image_linesize;
-            pd_last += s->image_linesize;
         }
     }
-    for (j = s->y_offset + s->cur_h; j < s->height; j++) {
-        for (i = 0; i < ls; i++)
-            pd[i] = pd_last[i];
-        pd      += s->image_linesize;
-        pd_last += s->image_linesize;
-    }
+
+    // Copy blended buffer into the frame and free
+    memcpy(p->data[0], buffer, s->image_linesize * s->height);
+    av_free(buffer);
 
     return 0;
 }
@@ -948,12 +1089,19 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
     AVDictionary *metadata  = NULL;
     uint32_t tag, length;
     int decode_next_dat = 0;
-    int ret = AVERROR_INVALIDDATA;
+    int ret;
 
     for (;;) {
         length = bytestream2_get_bytes_left(&s->gb);
         if (length <= 0) {
-            if (avctx->codec_id == AV_CODEC_ID_APNG && 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
@@ -963,12 +1111,14 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
             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);
@@ -978,34 +1128,51 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
                 ((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 (decode_ihdr_chunk(avctx, s, length) < 0)
+            if ((ret = decode_ihdr_chunk(avctx, s, length)) < 0)
                 goto fail;
             break;
         case MKTAG('p', 'H', 'Y', 's'):
-            if (decode_phys_chunk(avctx, s) < 0)
+            if ((ret = decode_phys_chunk(avctx, s)) < 0)
                 goto fail;
             break;
         case MKTAG('f', 'c', 'T', 'L'):
-            if (avctx->codec_id != AV_CODEC_ID_APNG)
+            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 (avctx->codec_id != AV_CODEC_ID_APNG)
+            if (!CONFIG_APNG_DECODER || avctx->codec_id != AV_CODEC_ID_APNG)
                 goto skip_tag;
-            if (!decode_next_dat)
+            if (!decode_next_dat) {
+                ret = AVERROR_INVALIDDATA;
                 goto fail;
+            }
             bytestream2_get_be32(&s->gb);
             length -= 4;
             /* fallthrough */
         case MKTAG('I', 'D', 'A', 'T'):
-            if (avctx->codec_id == AV_CODEC_ID_APNG && !decode_next_dat)
+            if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && !decode_next_dat)
                 goto skip_tag;
-            if (decode_idat_chunk(avctx, s, length, p) < 0)
+            if ((ret = decode_idat_chunk(avctx, s, length, p)) < 0)
                 goto fail;
             break;
         case MKTAG('P', 'L', 'T', 'E'):
@@ -1026,10 +1193,27 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
                 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 */
@@ -1042,10 +1226,38 @@ skip_tag:
         }
     }
 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")
@@ -1062,6 +1274,7 @@ exit_loop:
         }
     }
     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;
@@ -1070,6 +1283,7 @@ exit_loop:
 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;
 }
 
@@ -1095,11 +1309,11 @@ static int decode_frame_png(AVCodecContext *avctx,
     sig = bytestream2_get_be64(&s->gb);
     if (sig != PNGSIG &&
         sig != MNGSIG) {
-        av_log(avctx, AV_LOG_ERROR, "Missing png signature\n");
+        av_log(avctx, AV_LOG_ERROR, "Invalid PNG signature 0x%08"PRIX64".\n", sig);
         return AVERROR_INVALIDDATA;
     }
 
-    s->y = s->state = 0;
+    s->y = s->state = s->has_trns = 0;
 
     /* init the zlib */
     s->zstream.zalloc = ff_png_zalloc;
@@ -1114,6 +1328,12 @@ static int decode_frame_png(AVCodecContext *avctx,
     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;
 
@@ -1183,30 +1403,72 @@ end:
 }
 #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;
@@ -1220,6 +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);
@@ -1246,7 +1510,7 @@ AVCodec ff_apng_decoder = {
     .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   = CODEC_CAP_DR1 | CODEC_CAP_FRAME_THREADS /*| CODEC_CAP_DRAW_HORIZ_BAND*/,
+    .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS /*| AV_CODEC_CAP_DRAW_HORIZ_BAND*/,
 };
 #endif
 
@@ -1262,6 +1526,7 @@ AVCodec ff_png_decoder = {
     .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*/,
+    .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