Add a WebP decoder

Container and lossy decoding by Aneesh Dogra <aneesh@sugarlabs.org>
Lossless decoding by Justin Ruggles <justin.ruggles@gmail.com>

8 files changed, 1483 insertions, 10 deletions

diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index bb4f960356..b10526bb43 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -390,6 +390,7 @@ OBJS-$(CONFIG_VP6_DECODER)             += vp6.o vp56.o vp56data.o vp56dsp.o \
 OBJS-$(CONFIG_VP8_DECODER)             += vp8.o vp8dsp.o vp56rac.o
 OBJS-$(CONFIG_VQA_DECODER)             += vqavideo.o
 OBJS-$(CONFIG_WAVPACK_DECODER)         += wavpack.o
+OBJS-$(CONFIG_WEBP_DECODER)            += webp.o
 OBJS-$(CONFIG_WMALOSSLESS_DECODER)     += wmalosslessdec.o wma_common.o
 OBJS-$(CONFIG_WMAPRO_DECODER)          += wmaprodec.o wma.o wma_common.o
 OBJS-$(CONFIG_WMAV1_DECODER)           += wmadec.o wma.o wma_common.o aactab.o
diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
index d4531f2dff..f827ca3a31 100644
--- a/libavcodec/allcodecs.c
+++ b/libavcodec/allcodecs.c
@@ -253,6 +253,7 @@ void avcodec_register_all(void)
     REGISTER_DECODER(VP6F,              vp6f);
     REGISTER_DECODER(VP8,               vp8);
     REGISTER_DECODER(VQA,               vqa);
+    REGISTER_DECODER(WEBP,              webp);
     REGISTER_ENCDEC (WMV1,              wmv1);
     REGISTER_ENCDEC (WMV2,              wmv2);
     REGISTER_DECODER(WMV3,              wmv3);
diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 2a39b433c3..b894ee8ecc 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -273,6 +273,7 @@ enum AVCodecID {
     AV_CODEC_ID_AIC,
     AV_CODEC_ID_ESCAPE130,
     AV_CODEC_ID_G2M,
+    AV_CODEC_ID_WEBP,
 
     /* various PCM "codecs" */
     AV_CODEC_ID_FIRST_AUDIO = 0x10000,     ///< A dummy id pointing at the start of audio codecs
diff --git a/libavcodec/codec_desc.c b/libavcodec/codec_desc.c
index 90e489175c..abab828ec6 100644
--- a/libavcodec/codec_desc.c
+++ b/libavcodec/codec_desc.c
@@ -1228,6 +1228,14 @@ static const AVCodecDescriptor codec_descriptors[] = {
         .long_name = NULL_IF_CONFIG_SMALL("Go2Meeting"),
         .props     = AV_CODEC_PROP_LOSSY,
     },
+    {
+        .id        = AV_CODEC_ID_WEBP,
+        .type      = AVMEDIA_TYPE_VIDEO,
+        .name      = "webp",
+        .long_name = NULL_IF_CONFIG_SMALL("WebP"),
+        .props     = AV_CODEC_PROP_INTRA_ONLY | AV_CODEC_PROP_LOSSY |
+                     AV_CODEC_PROP_LOSSLESS,
+    },
 
     /* various PCM "codecs" */
     {
diff --git a/libavcodec/version.h b/libavcodec/version.h
index 980c5c5240..9775a650e4 100644
--- a/libavcodec/version.h
+++ b/libavcodec/version.h
@@ -27,7 +27,7 @@
  */
 
 #define LIBAVCODEC_VERSION_MAJOR 55
-#define LIBAVCODEC_VERSION_MINOR 18
+#define LIBAVCODEC_VERSION_MINOR 19
 #define LIBAVCODEC_VERSION_MICRO  0
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
diff --git a/libavcodec/vp8.c b/libavcodec/vp8.c
index 17b79f5fc4..3c60aa3409 100644
--- a/libavcodec/vp8.c
+++ b/libavcodec/vp8.c
@@ -1853,8 +1853,8 @@ static int vp8_decode_mb_row_sliced(AVCodecContext *avctx, void *tdata,
     return 0;
 }
 
-static int vp8_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
-                            AVPacket *avpkt)
+int ff_vp8_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
+                        AVPacket *avpkt)
 {
     VP8Context *s = avctx->priv_data;
     int ret, i, referenced, num_jobs;
@@ -2010,7 +2010,7 @@ err:
     return ret;
 }
 
-static av_cold int vp8_decode_free(AVCodecContext *avctx)
+av_cold int ff_vp8_decode_free(AVCodecContext *avctx)
 {
     VP8Context *s = avctx->priv_data;
     int i;
@@ -2033,7 +2033,7 @@ static av_cold int vp8_init_frames(VP8Context *s)
     return 0;
 }
 
-static av_cold int vp8_decode_init(AVCodecContext *avctx)
+av_cold int ff_vp8_decode_init(AVCodecContext *avctx)
 {
     VP8Context *s = avctx->priv_data;
     int ret;
@@ -2047,7 +2047,7 @@ static av_cold int vp8_decode_init(AVCodecContext *avctx)
     ff_vp8dsp_init(&s->vp8dsp);
 
     if ((ret = vp8_init_frames(s)) < 0) {
-        vp8_decode_free(avctx);
+        ff_vp8_decode_free(avctx);
         return ret;
     }
 
@@ -2062,7 +2062,7 @@ static av_cold int vp8_decode_init_thread_copy(AVCodecContext *avctx)
     s->avctx = avctx;
 
     if ((ret = vp8_init_frames(s)) < 0) {
-        vp8_decode_free(avctx);
+        ff_vp8_decode_free(avctx);
         return ret;
     }
 
@@ -2110,9 +2110,9 @@ AVCodec ff_vp8_decoder = {
     .type                  = AVMEDIA_TYPE_VIDEO,
     .id                    = AV_CODEC_ID_VP8,
     .priv_data_size        = sizeof(VP8Context),
-    .init                  = vp8_decode_init,
-    .close                 = vp8_decode_free,
-    .decode                = vp8_decode_frame,
+    .init                  = ff_vp8_decode_init,
+    .close                 = ff_vp8_decode_free,
+    .decode                = ff_vp8_decode_frame,
     .capabilities          = CODEC_CAP_DR1 | CODEC_CAP_FRAME_THREADS | CODEC_CAP_SLICE_THREADS,
     .flush                 = vp8_decode_flush,
     .long_name             = NULL_IF_CONFIG_SMALL("On2 VP8"),
diff --git a/libavcodec/vp8.h b/libavcodec/vp8.h
index 80f555f404..6555629806 100644
--- a/libavcodec/vp8.h
+++ b/libavcodec/vp8.h
@@ -269,4 +269,11 @@ typedef struct VP8Context {
     int mb_layout;
 } VP8Context;
 
+int ff_vp8_decode_init(AVCodecContext *avctx);
+
+int ff_vp8_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
+                        AVPacket *avpkt);
+
+int ff_vp8_decode_free(AVCodecContext *avctx);
+
 #endif /* AVCODEC_VP8_H */
diff --git a/libavcodec/webp.c b/libavcodec/webp.c
new file mode 100644
index 0000000000..8ad24f8fb7
--- /dev/null
+++ b/libavcodec/webp.c
@@ -0,0 +1,1455 @@
+/*
+ * WebP (.webp) image decoder
+ * Copyright (c) 2013 Aneesh Dogra <aneesh@sugarlabs.org>
+ * Copyright (c) 2013 Justin Ruggles <justin.ruggles@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * WebP image decoder
+ *
+ * @author Aneesh Dogra <aneesh@sugarlabs.org>
+ * Container and Lossy decoding
+ *
+ * @author Justin Ruggles <justin.ruggles@gmail.com>
+ * Lossless decoder
+ * Compressed alpha for lossy
+ *
+ * Unimplemented:
+ *   - Animation
+ *   - ICC profile
+ *   - Exif and XMP metadata
+ */
+
+#define BITSTREAM_READER_LE
+#include "libavutil/imgutils.h"
+#include "avcodec.h"
+#include "bytestream.h"
+#include "internal.h"
+#include "get_bits.h"
+#include "thread.h"
+#include "vp8.h"
+
+#define VP8X_FLAG_ANIMATION             0x02
+#define VP8X_FLAG_XMP_METADATA          0x04
+#define VP8X_FLAG_EXIF_METADATA         0x08
+#define VP8X_FLAG_ALPHA                 0x10
+#define VP8X_FLAG_ICC                   0x20
+
+#define MAX_PALETTE_SIZE                256
+#define MAX_CACHE_BITS                  11
+#define NUM_CODE_LENGTH_CODES           19
+#define HUFFMAN_CODES_PER_META_CODE     5
+#define NUM_LITERAL_CODES               256
+#define NUM_LENGTH_CODES                24
+#define NUM_DISTANCE_CODES              40
+#define NUM_SHORT_DISTANCES             120
+#define MAX_HUFFMAN_CODE_LENGTH         15
+
+static const uint16_t alphabet_sizes[HUFFMAN_CODES_PER_META_CODE] = {
+    NUM_LITERAL_CODES + NUM_LENGTH_CODES,
+    NUM_LITERAL_CODES, NUM_LITERAL_CODES, NUM_LITERAL_CODES,
+    NUM_DISTANCE_CODES
+};
+
+static const uint8_t code_length_code_order[NUM_CODE_LENGTH_CODES] = {
+    17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
+};
+
+static const int8_t lz77_distance_offsets[NUM_SHORT_DISTANCES][2] = {
+    {  0, 1 }, {  1, 0 }, {  1, 1 }, { -1, 1 }, {  0, 2 }, {  2, 0 }, {  1, 2 }, { -1, 2 },
+    {  2, 1 }, { -2, 1 }, {  2, 2 }, { -2, 2 }, {  0, 3 }, {  3, 0 }, {  1, 3 }, { -1, 3 },
+    {  3, 1 }, { -3, 1 }, {  2, 3 }, { -2, 3 }, {  3, 2 }, { -3, 2 }, {  0, 4 }, {  4, 0 },
+    {  1, 4 }, { -1, 4 }, {  4, 1 }, { -4, 1 }, {  3, 3 }, { -3, 3 }, {  2, 4 }, { -2, 4 },
+    {  4, 2 }, { -4, 2 }, {  0, 5 }, {  3, 4 }, { -3, 4 }, {  4, 3 }, { -4, 3 }, {  5, 0 },
+    {  1, 5 }, { -1, 5 }, {  5, 1 }, { -5, 1 }, {  2, 5 }, { -2, 5 }, {  5, 2 }, { -5, 2 },
+    {  4, 4 }, { -4, 4 }, {  3, 5 }, { -3, 5 }, {  5, 3 }, { -5, 3 }, {  0, 6 }, {  6, 0 },
+    {  1, 6 }, { -1, 6 }, {  6, 1 }, { -6, 1 }, {  2, 6 }, { -2, 6 }, {  6, 2 }, { -6, 2 },
+    {  4, 5 }, { -4, 5 }, {  5, 4 }, { -5, 4 }, {  3, 6 }, { -3, 6 }, {  6, 3 }, { -6, 3 },
+    {  0, 7 }, {  7, 0 }, {  1, 7 }, { -1, 7 }, {  5, 5 }, { -5, 5 }, {  7, 1 }, { -7, 1 },
+    {  4, 6 }, { -4, 6 }, {  6, 4 }, { -6, 4 }, {  2, 7 }, { -2, 7 }, {  7, 2 }, { -7, 2 },
+    {  3, 7 }, { -3, 7 }, {  7, 3 }, { -7, 3 }, {  5, 6 }, { -5, 6 }, {  6, 5 }, { -6, 5 },
+    {  8, 0 }, {  4, 7 }, { -4, 7 }, {  7, 4 }, { -7, 4 }, {  8, 1 }, {  8, 2 }, {  6, 6 },
+    { -6, 6 }, {  8, 3 }, {  5, 7 }, { -5, 7 }, {  7, 5 }, { -7, 5 }, {  8, 4 }, {  6, 7 },
+    { -6, 7 }, {  7, 6 }, { -7, 6 }, {  8, 5 }, {  7, 7 }, { -7, 7 }, {  8, 6 }, {  8, 7 }
+};
+
+enum AlphaCompression {
+    ALPHA_COMPRESSION_NONE,
+    ALPHA_COMPRESSION_VP8L,
+};
+
+enum AlphaFilter {
+    ALPHA_FILTER_NONE,
+    ALPHA_FILTER_HORIZONTAL,
+    ALPHA_FILTER_VERTICAL,
+    ALPHA_FILTER_GRADIENT,
+};
+
+enum TransformType {
+    PREDICTOR_TRANSFORM      = 0,
+    COLOR_TRANSFORM          = 1,
+    SUBTRACT_GREEN           = 2,
+    COLOR_INDEXING_TRANSFORM = 3,
+};
+
+enum PredictionMode {
+    PRED_MODE_BLACK,
+    PRED_MODE_L,
+    PRED_MODE_T,
+    PRED_MODE_TR,
+    PRED_MODE_TL,
+    PRED_MODE_AVG_T_AVG_L_TR,
+    PRED_MODE_AVG_L_TL,
+    PRED_MODE_AVG_L_T,
+    PRED_MODE_AVG_TL_T,
+    PRED_MODE_AVG_T_TR,
+    PRED_MODE_AVG_AVG_L_TL_AVG_T_TR,
+    PRED_MODE_SELECT,
+    PRED_MODE_ADD_SUBTRACT_FULL,
+    PRED_MODE_ADD_SUBTRACT_HALF,
+};
+
+enum HuffmanIndex {
+    HUFF_IDX_GREEN = 0,
+    HUFF_IDX_RED   = 1,
+    HUFF_IDX_BLUE  = 2,
+    HUFF_IDX_ALPHA = 3,
+    HUFF_IDX_DIST  = 4
+};
+
+/* The structure of WebP lossless is an optional series of transformation data,
+ * followed by the primary image. The primary image also optionally contains
+ * an entropy group mapping if there are multiple entropy groups. There is a
+ * basic image type called an "entropy coded image" that is used for all of
+ * these. The type of each entropy coded image is referred to by the
+ * specification as its role. */
+enum ImageRole {
+    /* Primary Image: Stores the actual pixels of the image. */
+    IMAGE_ROLE_ARGB,
+
+    /* Entropy Image: Defines which Huffman group to use for different areas of
+     *                the primary image. */
+    IMAGE_ROLE_ENTROPY,
+
+    /* Predictors: Defines which predictor type to use for different areas of
+     *             the primary image. */
+    IMAGE_ROLE_PREDICTOR,
+
+    /* Color Transform Data: Defines the color transformation for different
+     *                       areas of the primary image. */
+    IMAGE_ROLE_COLOR_TRANSFORM,
+
+    /* Color Index: Stored as an image of height == 1. */
+    IMAGE_ROLE_COLOR_INDEXING,
+
+    IMAGE_ROLE_NB,
+};
+
+typedef struct HuffReader {
+    VLC vlc;                            /* Huffman decoder context */
+    int simple;                         /* whether to use simple mode */
+    int nb_symbols;                     /* number of coded symbols */
+    uint16_t simple_symbols[2];         /* symbols for simple mode */
+} HuffReader;
+
+typedef struct ImageContext {
+    enum ImageRole role;                /* role of this image */
+    AVFrame *frame;                     /* AVFrame for data */
+    int color_cache_bits;               /* color cache size, log2 */
+    uint32_t *color_cache;              /* color cache data */
+    int nb_huffman_groups;              /* number of huffman groups */
+    HuffReader *huffman_groups;         /* reader for each huffman group */
+    int size_reduction;                 /* relative size compared to primary image, log2 */
+    int is_alpha_primary;
+} ImageContext;
+
+typedef struct WebPContext {
+    VP8Context v;                       /* VP8 Context used for lossy decoding */
+    GetBitContext gb;                   /* bitstream reader for main image chunk */
+    AVFrame *alpha_frame;               /* AVFrame for alpha data decompressed from VP8L */
+    AVCodecContext *avctx;              /* parent AVCodecContext */
+    int initialized;                    /* set once the VP8 context is initialized */
+    int has_alpha;                      /* has a separate alpha chunk */
+    enum AlphaCompression alpha_compression; /* compression type for alpha chunk */
+    enum AlphaFilter alpha_filter;      /* filtering method for alpha chunk */
+    uint8_t *alpha_data;                /* alpha chunk data */
+    int alpha_data_size;                /* alpha chunk data size */
+    int width;                          /* image width */
+    int height;                         /* image height */
+    int lossless;                       /* indicates lossless or lossy */
+
+    int nb_transforms;                  /* number of transforms */
+    enum TransformType transforms[4];   /* transformations used in the image, in order */
+    int reduced_width;                  /* reduced width for index image, if applicable */
+    int nb_huffman_groups;              /* number of huffman groups in the primary image */
+    ImageContext image[IMAGE_ROLE_NB];  /* image context for each role */
+} WebPContext;
+
+#define GET_PIXEL(frame, x, y) \
+    ((frame)->data[0] + (y) * frame->linesize[0] + 4 * (x))
+
+#define GET_PIXEL_COMP(frame, x, y, c) \
+    (*((frame)->data[0] + (y) * frame->linesize[0] + 4 * (x) + c))
+
+static void image_ctx_free(ImageContext *img)
+{
+    int i, j;
+
+    av_free(img->color_cache);
+    if (img->role != IMAGE_ROLE_ARGB && !img->is_alpha_primary)
+        av_frame_free(&img->frame);
+    if (img->huffman_groups) {
+        for (i = 0; i < img->nb_huffman_groups; i++) {
+            for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; j++)
+                ff_free_vlc(&img->huffman_groups[i * HUFFMAN_CODES_PER_META_CODE + j].vlc);
+        }
+        av_free(img->huffman_groups);
+    }
+    memset(img, 0, sizeof(*img));
+}
+
+
+/* Differs from get_vlc2() in the following ways:
+ *   - codes are bit-reversed
+ *   - assumes 8-bit table to make reversal simpler
+ *   - assumes max depth of 2 since the max code length for WebP is 15
+ */
+static av_always_inline int webp_get_vlc(GetBitContext *gb, VLC_TYPE (*table)[2])
+{
+    int n, nb_bits;
+    unsigned int index;
+    int code;
+
+    OPEN_READER(re, gb);
+    UPDATE_CACHE(re, gb);
+
+    index = SHOW_UBITS(re, gb, 8);
+    index = ff_reverse[index];
+    code  = table[index][0];
+    n     = table[index][1];
+
+    if (n < 0) {
+        LAST_SKIP_BITS(re, gb, 8);
+        UPDATE_CACHE(re, gb);
+
+        nb_bits = -n;
+
+        index = SHOW_UBITS(re, gb, nb_bits);
+        index = (ff_reverse[index] >> (8 - nb_bits)) + code;
+        code  = table[index][0];
+        n     = table[index][1];
+    }
+    SKIP_BITS(re, gb, n);
+
+    CLOSE_READER(re, gb);
+
+    return code;
+}
+
+static int huff_reader_get_symbol(HuffReader *r, GetBitContext *gb)
+{
+    if (r->simple) {
+        if (r->nb_symbols == 1)
+            return r->simple_symbols[0];
+        else
+            return r->simple_symbols[get_bits1(gb)];
+    } else
+        return webp_get_vlc(gb, r->vlc.table);
+}
+
+static int huff_reader_build_canonical(HuffReader *r, int *code_lengths,
+                                       int alphabet_size)
+{
+    int len, sym, code, ret;
+    int max_code_length = 0;
+    uint16_t *codes;
+
+    for (sym = 0; sym < alphabet_size; sym++)
+        max_code_length = FFMAX(max_code_length, code_lengths[sym]);
+
+    if (max_code_length == 0 || max_code_length > MAX_HUFFMAN_CODE_LENGTH)
+        return AVERROR(EINVAL);
+
+    codes = av_malloc(alphabet_size * sizeof(*codes));
+    if (!codes)
+        return AVERROR(ENOMEM);
+
+    code = 0;
+    r->nb_symbols = 0;
+    for (len = 1; len <= max_code_length; len++) {
+        for (sym = 0; sym < alphabet_size; sym++) {
+            if (code_lengths[sym] != len)
+                continue;
+            codes[sym] = code++;
+            r->nb_symbols++;
+        }
+        code <<= 1;
+    }
+    if (!r->nb_symbols) {
+        av_free(codes);
+        return AVERROR_INVALIDDATA;
+    }
+
+    ret = init_vlc(&r->vlc, 8, alphabet_size,
+                   code_lengths, sizeof(*code_lengths), sizeof(*code_lengths),
+                   codes, sizeof(*codes), sizeof(*codes), 0);
+    if (ret < 0) {
+        av_free(codes);
+        return ret;
+    }
+    r->simple = 0;
+
+    av_free(codes);
+    return 0;
+}
+
+static void read_huffman_code_simple(WebPContext *s, HuffReader *hc)
+{
+    hc->nb_symbols = get_bits1(&s->gb) + 1;
+
+    if (get_bits1(&s->gb))
+        hc->simple_symbols[0] = get_bits(&s->gb, 8);
+    else
+        hc->simple_symbols[0] = get_bits1(&s->gb);
+
+    if (hc->nb_symbols == 2)
+        hc->simple_symbols[1] = get_bits(&s->gb, 8);
+
+    hc->simple = 1;
+}
+
+static int read_huffman_code_normal(WebPContext *s, HuffReader *hc,
+                                    int alphabet_size)
+{
+    HuffReader code_len_hc = { { 0 }, 0, 0, { 0 } };
+    int *code_lengths = NULL;
+    int code_length_code_lengths[NUM_CODE_LENGTH_CODES] = { 0 };
+    int i, symbol, max_symbol, prev_code_len, ret;
+    int num_codes = 4 + get_bits(&s->gb, 4);
+
+    if (num_codes > NUM_CODE_LENGTH_CODES)
+        return AVERROR_INVALIDDATA;
+
+    for (i = 0; i < num_codes; i++)
+        code_length_code_lengths[code_length_code_order[i]] = get_bits(&s->gb, 3);
+
+    ret = huff_reader_build_canonical(&code_len_hc, code_length_code_lengths,
+                                      NUM_CODE_LENGTH_CODES);
+    if (ret < 0)
+        goto finish;
+
+    code_lengths = av_mallocz_array(alphabet_size, sizeof(*code_lengths));
+    if (!code_lengths) {
+        ret = AVERROR(ENOMEM);
+        goto finish;
+    }
+
+    if (get_bits1(&s->gb)) {
+        int bits   = 2 + 2 * get_bits(&s->gb, 3);
+        max_symbol = 2 + get_bits(&s->gb, bits);
+        if (max_symbol > alphabet_size) {
+            av_log(s->avctx, AV_LOG_ERROR, "max symbol %d > alphabet size %d\n",
+                   max_symbol, alphabet_size);
+            ret = AVERROR_INVALIDDATA;
+            goto finish;
+        }
+    } else {
+        max_symbol = alphabet_size;
+    }
+
+    prev_code_len = 8;
+    symbol        = 0;
+    while (symbol < alphabet_size) {
+        int code_len;
+
+        if (!max_symbol--)
+            break;
+        code_len = huff_reader_get_symbol(&code_len_hc, &s->gb);
+        if (code_len < 16) {
+            /* Code length code [0..15] indicates literal code lengths. */
+            code_lengths[symbol++] = code_len;
+            if (code_len)
+                prev_code_len = code_len;
+        } else {
+            int repeat = 0, length = 0;
+            switch (code_len) {
+            case 16:
+                /* Code 16 repeats the previous non-zero value [3..6] times,
+                 * i.e., 3 + ReadBits(2) times. If code 16 is used before a
+                 * non-zero value has been emitted, a value of 8 is repeated. */
+                repeat = 3 + get_bits(&s->gb, 2);
+                length = prev_code_len;
+                break;
+            case 17:
+                /* Code 17 emits a streak of zeros [3..10], i.e.,
+                 * 3 + ReadBits(3) times. */
+                repeat = 3 + get_bits(&s->gb, 3);
+                break;
+            case 18:
+                /* Code 18 emits a streak of zeros of length [11..138], i.e.,
+                 * 11 + ReadBits(7) times. */
+                repeat = 11 + get_bits(&s->gb, 7);
+                break;
+            }
+            if (symbol + repeat > alphabet_size) {
+                av_log(s->avctx, AV_LOG_ERROR,
+                       "invalid symbol %d + repeat %d > alphabet size %d\n",
+                       symbol, repeat, alphabet_size);
+                ret = AVERROR_INVALIDDATA;
+                goto finish;
+            }
+            while (repeat-- > 0)
+                code_lengths[symbol++] = length;
+        }
+    }
+
+    ret = huff_reader_build_canonical(hc, code_lengths, alphabet_size);
+
+finish:
+    ff_free_vlc(&code_len_hc.vlc);
+    av_free(code_lengths);
+    return ret;
+}
+
+static int decode_entropy_coded_image(WebPContext *s, enum ImageRole role,
+                                      int w, int h);
+
+#define PARSE_BLOCK_SIZE(w, h) do {                                         \
+    block_bits = get_bits(&s->gb, 3) + 2;                                   \
+    blocks_w   = FFALIGN((w), 1 << block_bits) >> block_bits;               \
+    blocks_h   = FFALIGN((h), 1 << block_bits) >> block_bits;               \
+} while (0)
+
+static int decode_entropy_image(WebPContext *s)
+{
+    ImageContext *img;
+    int ret, block_bits, width, blocks_w, blocks_h, x, y, max;
+
+    width = s->width;
+    if (s->reduced_width > 0)
+        width = s->reduced_width;
+
+    PARSE_BLOCK_SIZE(width, s->height);
+
+    ret = decode_entropy_coded_image(s, IMAGE_ROLE_ENTROPY, blocks_w, blocks_h);
+    if (ret < 0)
+        return ret;
+
+    img = &s->image[IMAGE_ROLE_ENTROPY];
+    img->size_reduction = block_bits;
+
+    /* the number of huffman groups is determined by the maximum group number
+     * coded in the entropy image */
+    max = 0;
+    for (y = 0; y < img->frame->height; y++) {
+        for (x = 0; x < img->frame->width; x++) {
+            int p = GET_PIXEL_COMP(img->frame, x, y, 2);
+            max = FFMAX(max, p);
+        }
+    }
+    s->nb_huffman_groups = max + 1;
+
+    return 0;
+}
+
+static int parse_transform_predictor(WebPContext *s)
+{
+    int block_bits, blocks_w, blocks_h, ret;
+
+    PARSE_BLOCK_SIZE(s->width, s->height);
+
+    ret = decode_entropy_coded_image(s, IMAGE_ROLE_PREDICTOR, blocks_w,
+                                     blocks_h);
+    if (ret < 0)
+        return ret;
+
+    s->image[IMAGE_ROLE_PREDICTOR].size_reduction = block_bits;
+
+    return 0;
+}
+
+static int parse_transform_color(WebPContext *s)
+{
+    int block_bits, blocks_w, blocks_h, ret;
+
+    PARSE_BLOCK_SIZE(s->width, s->height);
+
+    ret = decode_entropy_coded_image(s, IMAGE_ROLE_COLOR_TRANSFORM, blocks_w,
+                                     blocks_h);
+    if (ret < 0)
+        return ret;
+
+    s->image[IMAGE_ROLE_COLOR_TRANSFORM].size_reduction = block_bits;
+
+    return 0;
+}
+
+static int parse_transform_color_indexing(WebPContext *s)
+{
+    ImageContext *img;
+    int width_bits, index_size, ret, x;
+    uint8_t *ct;
+
+    index_size = get_bits(&s->gb, 8) + 1;
+
+    if (index_size <= 2)
+        width_bits = 3;
+    else if (index_size <= 4)
+        width_bits = 2;
+    else if (index_size <= 16)
+        width_bits = 1;
+    else
+        width_bits = 0;
+
+    ret = decode_entropy_coded_image(s, IMAGE_ROLE_COLOR_INDEXING,
+                                     index_size, 1);
+    if (ret < 0)
+        return ret;
+
+    img = &s->image[IMAGE_ROLE_COLOR_INDEXING];
+    img->size_reduction = width_bits;
+    if (width_bits > 0)
+        s->reduced_width = (s->width + ((1 << width_bits) - 1)) >> width_bits;
+
+    /* color index values are delta-coded */
+    ct  = img->frame->data[0] + 4;
+    for (x = 4; x < img->frame->width * 4; x++, ct++)
+        ct[0] += ct[-4];
+
+    return 0;
+}
+
+static HuffReader *get_huffman_group(WebPContext *s, ImageContext *img,
+                                     int x, int y)
+{
+    ImageContext *gimg = &s->image[IMAGE_ROLE_ENTROPY];
+    int group = 0;
+
+    if (gimg->size_reduction > 0) {
+        int group_x = x >> gimg->size_reduction;
+        int group_y = y >> gimg->size_reduction;
+        group       = GET_PIXEL_COMP(gimg->frame, group_x, group_y, 2);
+    }
+
+    return &img->huffman_groups[group * HUFFMAN_CODES_PER_META_CODE];
+}
+
+static av_always_inline void color_cache_put(ImageContext *img, uint32_t c)
+{
+    uint32_t cache_idx = (0x1E35A7BD * c) >> (32 - img->color_cache_bits);
+    img->color_cache[cache_idx] = c;
+}
+
+static int decode_entropy_coded_image(WebPContext *s, enum ImageRole role,
+                                      int w, int h)
+{
+    ImageContext *img;
+    HuffReader *hg;
+    int i, j, ret, x, y, width;
+
+    img       = &s->image[role];
+    img->role = role;
+
+    if (!img->frame) {
+        img->frame = av_frame_alloc();
+        if (!img->frame)
+            return AVERROR(ENOMEM);
+    }
+
+    img->frame->format = AV_PIX_FMT_ARGB;
+    img->frame->width  = w;
+    img->frame->height = h;
+
+    if (role == IMAGE_ROLE_ARGB && !img->is_alpha_primary) {
+        ThreadFrame pt = { .f = img->frame };
+        ret = ff_thread_get_buffer(s->avctx, &pt, 0);
+    } else
+        ret = av_frame_get_buffer(img->frame, 1);
+    if (ret < 0)
+        return ret;
+
+    if (get_bits1(&s->gb)) {
+        img->color_cache_bits = get_bits(&s->gb, 4);
+        if (img->color_cache_bits < 1 || img->color_cache_bits > 11) {
+            av_log(s->avctx, AV_LOG_ERROR, "invalid color cache bits: %d\n",
+                   img->color_cache_bits);
+            return AVERROR_INVALIDDATA;
+        }
+        img->color_cache = av_mallocz_array(1 << img->color_cache_bits,
+                                            sizeof(*img->color_cache));
+        if (!img->color_cache)
+            return AVERROR(ENOMEM);
+    } else {
+        img->color_cache_bits = 0;
+    }
+
+    img->nb_huffman_groups = 1;
+    if (role == IMAGE_ROLE_ARGB && get_bits1(&s->gb)) {
+        ret = decode_entropy_image(s);
+        if (ret < 0)
+            return ret;
+        img->nb_huffman_groups = s->nb_huffman_groups;
+    }
+    img->huffman_groups = av_mallocz_array(img->nb_huffman_groups *
+                                           HUFFMAN_CODES_PER_META_CODE,
+                                           sizeof(*img->huffman_groups));
+    if (!img->huffman_groups)
+        return AVERROR(ENOMEM);
+
+    for (i = 0; i < img->nb_huffman_groups; i++) {
+        hg = &img->huffman_groups[i * HUFFMAN_CODES_PER_META_CODE];
+        for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; j++) {
+            int alphabet_size = alphabet_sizes[j];
+            if (!j && img->color_cache_bits > 0)
+                alphabet_size += 1 << img->color_cache_bits;
+
+            if (get_bits1(&s->gb)) {
+                read_huffman_code_simple(s, &hg[j]);
+            } else {
+                ret = read_huffman_code_normal(s, &hg[j], alphabet_size);
+                if (ret < 0)
+                    return ret;
+            }
+        }
+    }
+
+    width = img->frame->width;
+    if (role == IMAGE_ROLE_ARGB && s->reduced_width > 0)
+        width = s->reduced_width;
+
+    x = 0; y = 0;
+    while (y < img->frame->height) {
+        int v;
+
+        hg = get_huffman_group(s, img, x, y);
+        v = huff_reader_get_symbol(&hg[HUFF_IDX_GREEN], &s->gb);
+        if (v < NUM_LITERAL_CODES) {
+            /* literal pixel values */
+            uint8_t *p = GET_PIXEL(img->frame, x, y);
+            p[2] = v;
+            p[1] = huff_reader_get_symbol(&hg[HUFF_IDX_RED],   &s->gb);
+            p[3] = huff_reader_get_symbol(&hg[HUFF_IDX_BLUE],  &s->gb);
+            p[0] = huff_reader_get_symbol(&hg[HUFF_IDX_ALPHA], &s->gb);
+            if (img->color_cache_bits)
+                color_cache_put(img, AV_RB32(p));
+            x++;
+            if (x == width) {
+                x = 0;
+                y++;
+            }
+        } else if (v < NUM_LITERAL_CODES + NUM_LENGTH_CODES) {
+            /* LZ77 backwards mapping */
+            int prefix_code, length, distance, ref_x, ref_y;
+
+            /* parse length and distance */
+            prefix_code = v - NUM_LITERAL_CODES;
+            if (prefix_code < 4) {
+                length = prefix_code + 1;
+            } else {
+                int extra_bits = (prefix_code - 2) >> 1;
+                int offset     = 2 + (prefix_code & 1) << extra_bits;
+                length = offset + get_bits(&s->gb, extra_bits) + 1;
+            }
+            prefix_code = huff_reader_get_symbol(&hg[HUFF_IDX_DIST], &s->gb);
+            if (prefix_code < 4) {
+                distance = prefix_code + 1;
+            } else {
+                int extra_bits = prefix_code - 2 >> 1;
+                int offset     = 2 + (prefix_code & 1) << extra_bits;
+                distance = offset + get_bits(&s->gb, extra_bits) + 1;
+            }
+
+            /* find reference location */
+            if (distance <= NUM_SHORT_DISTANCES) {
+                int xi = lz77_distance_offsets[distance - 1][0];
+                int yi = lz77_distance_offsets[distance - 1][1];
+                distance = FFMAX(1, xi + yi * width);
+            } else {
+                distance -= NUM_SHORT_DISTANCES;
+            }
+            ref_x = x;
+            ref_y = y;
+            if (distance <= x) {
+                ref_x -= distance;
+                distance = 0;
+            } else {
+                ref_x = 0;
+                distance -= x;
+            }
+            while (distance >= width) {
+                ref_y--;
+                distance -= width;
+            }
+            if (distance > 0) {
+                ref_x = width - distance;
+                ref_y--;
+            }
+            ref_x = FFMAX(0, ref_x);
+            ref_y = FFMAX(0, ref_y);
+
+            /* copy pixels
+             * source and dest regions can overlap and wrap lines, so just
+             * copy per-pixel */
+            for (i = 0; i < length; i++) {
+                uint8_t *p_ref = GET_PIXEL(img->frame, ref_x, ref_y);
+                uint8_t *p     = GET_PIXEL(img->frame,     x,     y);
+
+                AV_COPY32(p, p_ref);
+                if (img->color_cache_bits)
+                    color_cache_put(img, AV_RB32(p));
+                x++;
+                ref_x++;
+                if (x == width) {
+                    x = 0;
+                    y++;
+                }
+                if (ref_x == width) {
+                    ref_x = 0;
+                    ref_y++;
+                }
+                if (y == img->frame->height || ref_y == img->frame->height)
+                    break;
+            }
+        } else {
+            /* read from color cache */
+            uint8_t *p = GET_PIXEL(img->frame, x, y);
+            int cache_idx = v - (NUM_LITERAL_CODES + NUM_LENGTH_CODES);
+
+            if (!img->color_cache_bits) {
+                av_log(s->avctx, AV_LOG_ERROR, "color cache not found\n");
+                return AVERROR_INVALIDDATA;
+            }
+            if (cache_idx >= 1 << img->color_cache_bits) {
+                av_log(s->avctx, AV_LOG_ERROR,
+                       "color cache index out-of-bounds\n");
+                return AVERROR_INVALIDDATA;
+            }
+            AV_WB32(p, img->color_cache[cache_idx]);
+            x++;
+            if (x == width) {
+                x = 0;
+                y++;
+            }
+        }
+    }
+
+    return 0;
+}
+
+/* PRED_MODE_BLACK */
+static void inv_predict_0(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    AV_WB32(p, 0xFF000000);
+}
+
+/* PRED_MODE_L */
+static void inv_predict_1(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    AV_COPY32(p, p_l);
+}
+
+/* PRED_MODE_T */
+static void inv_predict_2(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    AV_COPY32(p, p_t);
+}
+
+/* PRED_MODE_TR */
+static void inv_predict_3(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    AV_COPY32(p, p_tr);
+}
+
+/* PRED_MODE_TL */
+static void inv_predict_4(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    AV_COPY32(p, p_tl);
+}
+
+/* PRED_MODE_AVG_T_AVG_L_TR */
+static void inv_predict_5(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = p_t[0] + (p_l[0] + p_tr[0] >> 1) >> 1;
+    p[1] = p_t[1] + (p_l[1] + p_tr[1] >> 1) >> 1;
+    p[2] = p_t[2] + (p_l[2] + p_tr[2] >> 1) >> 1;
+    p[3] = p_t[3] + (p_l[3] + p_tr[3] >> 1) >> 1;
+}
+
+/* PRED_MODE_AVG_L_TL */
+static void inv_predict_6(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = p_l[0] + p_tl[0] >> 1;
+    p[1] = p_l[1] + p_tl[1] >> 1;
+    p[2] = p_l[2] + p_tl[2] >> 1;
+    p[3] = p_l[3] + p_tl[3] >> 1;
+}
+
+/* PRED_MODE_AVG_L_T */
+static void inv_predict_7(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = p_l[0] + p_t[0] >> 1;
+    p[1] = p_l[1] + p_t[1] >> 1;
+    p[2] = p_l[2] + p_t[2] >> 1;
+    p[3] = p_l[3] + p_t[3] >> 1;
+}
+
+/* PRED_MODE_AVG_TL_T */
+static void inv_predict_8(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = p_tl[0] + p_t[0] >> 1;
+    p[1] = p_tl[1] + p_t[1] >> 1;
+    p[2] = p_tl[2] + p_t[2] >> 1;
+    p[3] = p_tl[3] + p_t[3] >> 1;
+}
+
+/* PRED_MODE_AVG_T_TR */
+static void inv_predict_9(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                          const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = p_t[0] + p_tr[0] >> 1;
+    p[1] = p_t[1] + p_tr[1] >> 1;
+    p[2] = p_t[2] + p_tr[2] >> 1;
+    p[3] = p_t[3] + p_tr[3] >> 1;
+}
+
+/* PRED_MODE_AVG_AVG_L_TL_AVG_T_TR */
+static void inv_predict_10(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                           const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = (p_l[0] + p_tl[0] >> 1) + (p_t[0] + p_tr[0] >> 1) >> 1;
+    p[1] = (p_l[1] + p_tl[1] >> 1) + (p_t[1] + p_tr[1] >> 1) >> 1;
+    p[2] = (p_l[2] + p_tl[2] >> 1) + (p_t[2] + p_tr[2] >> 1) >> 1;
+    p[3] = (p_l[3] + p_tl[3] >> 1) + (p_t[3] + p_tr[3] >> 1) >> 1;
+}
+
+/* PRED_MODE_SELECT */
+static void inv_predict_11(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                           const uint8_t *p_t, const uint8_t *p_tr)
+{
+    int diff = (FFABS(p_l[0] - p_tl[0]) - FFABS(p_t[0] - p_tl[0])) +
+               (FFABS(p_l[1] - p_tl[1]) - FFABS(p_t[1] - p_tl[1])) +
+               (FFABS(p_l[2] - p_tl[2]) - FFABS(p_t[2] - p_tl[2])) +
+               (FFABS(p_l[3] - p_tl[3]) - FFABS(p_t[3] - p_tl[3]));
+    if (diff <= 0)
+        AV_COPY32(p, p_t);
+    else
+        AV_COPY32(p, p_l);
+}
+
+/* PRED_MODE_ADD_SUBTRACT_FULL */
+static void inv_predict_12(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                           const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = av_clip_uint8(p_l[0] + p_t[0] - p_tl[0]);
+    p[1] = av_clip_uint8(p_l[1] + p_t[1] - p_tl[1]);
+    p[2] = av_clip_uint8(p_l[2] + p_t[2] - p_tl[2]);
+    p[3] = av_clip_uint8(p_l[3] + p_t[3] - p_tl[3]);
+}
+
+static av_always_inline uint8_t clamp_add_subtract_half(int a, int b, int c)
+{
+    int d = a + b >> 1;
+    return av_clip_uint8(d + (d - c) / 2);
+}
+
+/* PRED_MODE_ADD_SUBTRACT_HALF */
+static void inv_predict_13(uint8_t *p, const uint8_t *p_l, const uint8_t *p_tl,
+                           const uint8_t *p_t, const uint8_t *p_tr)
+{
+    p[0] = clamp_add_subtract_half(p_l[0], p_t[0], p_tl[0]);
+    p[1] = clamp_add_subtract_half(p_l[1], p_t[1], p_tl[1]);
+    p[2] = clamp_add_subtract_half(p_l[2], p_t[2], p_tl[2]);
+    p[3] = clamp_add_subtract_half(p_l[3], p_t[3], p_tl[3]);
+}
+
+typedef void (*inv_predict_func)(uint8_t *p, const uint8_t *p_l,
+                                 const uint8_t *p_tl, const uint8_t *p_t,
+                                 const uint8_t *p_tr);
+
+static const inv_predict_func inverse_predict[14] = {
+    inv_predict_0,  inv_predict_1,  inv_predict_2,  inv_predict_3,
+    inv_predict_4,  inv_predict_5,  inv_predict_6,  inv_predict_7,
+    inv_predict_8,  inv_predict_9,  inv_predict_10, inv_predict_11,
+    inv_predict_12, inv_predict_13,
+};
+
+static void inverse_prediction(AVFrame *frame, enum PredictionMode m, int x, int y)
+{
+    uint8_t *dec, *p_l, *p_tl, *p_t, *p_tr;
+    uint8_t p[4];
+
+    dec  = GET_PIXEL(frame, x,     y);
+    p_l  = GET_PIXEL(frame, x - 1, y);
+    p_tl = GET_PIXEL(frame, x - 1, y - 1);
+    p_t  = GET_PIXEL(frame, x,     y - 1);
+    if (x == frame->width - 1)
+        p_tr = GET_PIXEL(frame, 0, y);
+    else
+        p_tr = GET_PIXEL(frame, x + 1, y - 1);
+
+    inverse_predict[m](p, p_l, p_tl, p_t, p_tr);
+
+    dec[0] += p[0];
+    dec[1] += p[1];
+    dec[2] += p[2];
+    dec[3] += p[3];
+}
+
+static int apply_predictor_transform(WebPContext *s)
+{
+    ImageContext *img  = &s->image[IMAGE_ROLE_ARGB];
+    ImageContext *pimg = &s->image[IMAGE_ROLE_PREDICTOR];
+    int x, y;
+
+    for (y = 0; y < img->frame->height; y++) {
+        for (x = 0; x < img->frame->width; x++) {
+            int tx = x >> pimg->size_reduction;
+            int ty = y >> pimg->size_reduction;
+            enum PredictionMode m = GET_PIXEL_COMP(pimg->frame, tx, ty, 2);
+
+            if (x == 0) {
+                if (y == 0)
+                    m = PRED_MODE_BLACK;
+                else
+                    m = PRED_MODE_T;
+            } else if (y == 0)
+                m = PRED_MODE_L;
+
+            if (m > 13) {
+                av_log(s->avctx, AV_LOG_ERROR,
+                       "invalid predictor mode: %d\n", m);
+                return AVERROR_INVALIDDATA;
+            }
+            inverse_prediction(img->frame, m, x, y);
+        }
+    }
+    return 0;
+}
+
+static av_always_inline uint8_t color_transform_delta(uint8_t color_pred,
+                                                      uint8_t color)
+{
+    return (int)ff_u8_to_s8(color_pred) * ff_u8_to_s8(color) >> 5;
+}
+
+static int apply_color_transform(WebPContext *s)
+{
+    ImageContext *img, *cimg;
+    int x, y, cx, cy;
+    uint8_t *p, *cp;
+
+    img  = &s->image[IMAGE_ROLE_ARGB];
+    cimg = &s->image[IMAGE_ROLE_COLOR_TRANSFORM];
+
+    for (y = 0; y < img->frame->height; y++) {
+        for (x = 0; x < img->frame->width; x++) {
+            cx = x >> cimg->size_reduction;
+            cy = y >> cimg->size_reduction;
+            cp = GET_PIXEL(cimg->frame, cx, cy);
+            p  = GET_PIXEL(img->frame,   x,  y);
+
+            p[1] += color_transform_delta(cp[3], p[2]);
+            p[3] += color_transform_delta(cp[2], p[2]) +
+                    color_transform_delta(cp[1], p[1]);
+        }
+    }
+    return 0;
+}
+
+static int apply_subtract_green_transform(WebPContext *s)
+{
+    int x, y;
+    ImageContext *img = &s->image[IMAGE_ROLE_ARGB];
+
+    for (y = 0; y < img->frame->height; y++) {
+        for (x = 0; x < img->frame->width; x++) {
+            uint8_t *p = GET_PIXEL(img->frame, x, y);
+            p[1] += p[2];
+            p[3] += p[2];
+        }
+    }
+    return 0;
+}
+
+static int apply_color_indexing_transform(WebPContext *s)
+{
+    ImageContext *img;
+    ImageContext *pal;
+    int i, x, y;
+    uint8_t *p, *pi;
+
+    img = &s->image[IMAGE_ROLE_ARGB];
+    pal = &s->image[IMAGE_ROLE_COLOR_INDEXING];
+
+    if (pal->size_reduction > 0) {
+        GetBitContext gb_g;
+        uint8_t *line;
+        int pixel_bits = 8 >> pal->size_reduction;
+
+        line = av_malloc(img->frame->linesize[0]);
+        if (!line)
+            return AVERROR(ENOMEM);
+
+        for (y = 0; y < img->frame->height; y++) {
+            p = GET_PIXEL(img->frame, 0, y);
+            memcpy(line, p, img->frame->linesize[0]);
+            init_get_bits(&gb_g, line, img->frame->linesize[0] * 8);
+            skip_bits(&gb_g, 16);
+            i = 0;
+            for (x = 0; x < img->frame->width; x++) {
+                p    = GET_PIXEL(img->frame, x, y);
+                p[2] = get_bits(&gb_g, pixel_bits);
+                i++;
+                if (i == 1 << pal->size_reduction) {
+                    skip_bits(&gb_g, 24);
+                    i = 0;
+                }
+            }
+        }
+        av_free(line);
+    }
+
+    for (y = 0; y < img->frame->height; y++) {
+        for (x = 0; x < img->frame->width; x++) {
+            p = GET_PIXEL(img->frame, x, y);
+            i = p[2];
+            if (i >= pal->frame->width) {
+                av_log(s->avctx, AV_LOG_ERROR, "invalid palette index %d\n", i);
+                return AVERROR_INVALIDDATA;
+            }
+            pi = GET_PIXEL(pal->frame, i, 0);
+            AV_COPY32(p, pi);
+        }
+    }
+
+    return 0;
+}
+
+static int vp8_lossless_decode_frame(AVCodecContext *avctx, AVFrame *p,
+                                     int *got_frame, uint8_t *data_start,
+                                     unsigned int data_size, int is_alpha_chunk)
+{
+    WebPContext *s = avctx->priv_data;
+    int w, h, ret, i;
+
+    if (!is_alpha_chunk) {
+        s->lossless = 1;
+        avctx->pix_fmt = AV_PIX_FMT_ARGB;
+    }
+
+    ret = init_get_bits(&s->gb, data_start, data_size * 8);
+    if (ret < 0)
+        return ret;
+
+    if (!is_alpha_chunk) {
+        if (get_bits(&s->gb, 8) != 0x2F) {
+            av_log(avctx, AV_LOG_ERROR, "Invalid WebP Lossless signature\n");
+            return AVERROR_INVALIDDATA;
+        }
+
+        w = get_bits(&s->gb, 14) + 1;
+        h = get_bits(&s->gb, 14) + 1;
+        if (s->width && s->width != w) {
+            av_log(avctx, AV_LOG_WARNING, "Width mismatch. %d != %d\n",
+                   s->width, w);
+        }
+        s->width = w;
+        if (s->height && s->height != h) {
+            av_log(avctx, AV_LOG_WARNING, "Height mismatch. %d != %d\n",
+                   s->width, w);
+        }
+        s->height = h;
+        ret = av_image_check_size(s->width, s->height, 0, avctx);
+        if (ret < 0)
+            return ret;
+        avcodec_set_dimensions(avctx, s->width, s->height);
+
+        s->has_alpha = get_bits1(&s->gb);
+
+        if (get_bits(&s->gb, 3) != 0x0) {
+            av_log(avctx, AV_LOG_ERROR, "Invalid WebP Lossless version\n");
+            return AVERROR_INVALIDDATA;
+        }
+    } else {
+        if (!s->width || !s->height)
+            return AVERROR_BUG;
+        w = s->width;
+        h = s->height;
+    }
+
+    /* parse transformations */
+    s->nb_transforms = 0;
+    s->reduced_width = 0;
+    while (get_bits1(&s->gb)) {
+        enum TransformType transform = get_bits(&s->gb, 2);
+        s->transforms[s->nb_transforms++] = transform;
+        switch (transform) {
+        case PREDICTOR_TRANSFORM:
+            ret = parse_transform_predictor(s);
+            break;
+        case COLOR_TRANSFORM:
+            ret = parse_transform_color(s);
+            break;
+        case COLOR_INDEXING_TRANSFORM:
+            ret = parse_transform_color_indexing(s);
+            break;
+        }
+        if (ret < 0)
+            goto free_and_return;
+    }
+
+    /* decode primary image */
+    s->image[IMAGE_ROLE_ARGB].frame = p;
+    if (is_alpha_chunk)
+        s->image[IMAGE_ROLE_ARGB].is_alpha_primary = 1;
+    ret = decode_entropy_coded_image(s, IMAGE_ROLE_ARGB, w, h);
+    if (ret < 0) {
+        av_frame_free(&p);
+        goto free_and_return;
+    }
+
+    /* apply transformations */
+    for (i = s->nb_transforms - 1; i >= 0; i--) {
+        switch (s->transforms[i]) {
+        case PREDICTOR_TRANSFORM:
+            ret = apply_predictor_transform(s);
+            break;
+        case COLOR_TRANSFORM:
+            ret = apply_color_transform(s);
+            break;
+        case SUBTRACT_GREEN:
+            ret = apply_subtract_green_transform(s);
+            break;
+        case COLOR_INDEXING_TRANSFORM:
+            ret = apply_color_indexing_transform(s);
+            break;
+        }
+        if (ret < 0) {
+            av_frame_free(&p);
+            goto free_and_return;
+        }
+    }
+
+    *got_frame   = 1;
+    p->pict_type = AV_PICTURE_TYPE_I;
+    p->key_frame = 1;
+    ret          = data_size;
+
+free_and_return:
+    for (i = 0; i < IMAGE_ROLE_NB; i++)
+        image_ctx_free(&s->image[i]);
+
+    return ret;
+}
+
+static void alpha_inverse_prediction(AVFrame *frame, enum AlphaFilter m)
+{
+    int x, y, ls;
+    uint8_t *dec;
+
+    ls = frame->linesize[3];
+
+    /* filter first row using horizontal filter */
+    dec = frame->data[3] + 1;
+    for (x = 1; x < frame->width; x++, dec++)
+        *dec += *(dec - 1);
+
+    /* filter first column using vertical filter */
+    dec = frame->data[3] + ls;
+    for (y = 1; y < frame->height; y++, dec += ls)
+        *dec += *(dec - ls);
+
+    /* filter the rest using the specified filter */
+    switch (m) {
+    case ALPHA_FILTER_HORIZONTAL:
+        for (y = 1; y < frame->height; y++) {
+            dec = frame->data[3] + y * ls + 1;
+            for (x = 1; x < frame->width; x++, dec++)
+                *dec += *(dec - 1);
+        }
+        break;
+    case ALPHA_FILTER_VERTICAL:
+        for (y = 1; y < frame->height; y++) {
+            dec = frame->data[3] + y * ls + 1;
+            for (x = 1; x < frame->width; x++, dec++)
+                *dec += *(dec - ls);
+        }
+        break;
+    case ALPHA_FILTER_GRADIENT:
+        for (y = 1; y < frame->height; y++) {
+            dec = frame->data[3] + y * ls + 1;
+            for (x = 1; x < frame->width; x++, dec++)
+                dec[0] += av_clip_uint8(*(dec - 1) + *(dec - ls) - *(dec - ls - 1));
+        }
+        break;
+    }
+}
+
+static int vp8_lossy_decode_alpha(AVCodecContext *avctx, AVFrame *p,
+                                  uint8_t *data_start,
+                                  unsigned int data_size)
+{
+    WebPContext *s = avctx->priv_data;
+    int x, y, ret;
+
+    if (s->alpha_compression == ALPHA_COMPRESSION_NONE) {
+        GetByteContext gb;
+
+        bytestream2_init(&gb, data_start, data_size);
+        for (y = 0; y < s->height; y++)
+            bytestream2_get_buffer(&gb, p->data[3] + p->linesize[3] * y,
+                                   s->width);
+    } else if (s->alpha_compression == ALPHA_COMPRESSION_VP8L) {
+        uint8_t *ap, *pp;
+        int alpha_got_frame = 0;
+
+        s->alpha_frame = av_frame_alloc();
+        if (!s->alpha_frame)
+            return AVERROR(ENOMEM);
+
+        ret = vp8_lossless_decode_frame(avctx, s->alpha_frame, &alpha_got_frame,
+                                        data_start, data_size, 1);
+        if (ret < 0) {
+            av_frame_free(&s->alpha_frame);
+            return ret;
+        }
+        if (!alpha_got_frame) {
+            av_frame_free(&s->alpha_frame);
+            return AVERROR_INVALIDDATA;
+        }
+
+        /* copy green component of alpha image to alpha plane of primary image */
+        for (y = 0; y < s->height; y++) {
+            ap = GET_PIXEL(s->alpha_frame, 0, y) + 2;
+            pp = p->data[3] + p->linesize[3] * y;
+            for (x = 0; x < s->width; x++) {
+                *pp = *ap;
+                pp++;
+                ap += 4;
+            }
+        }
+        av_frame_free(&s->alpha_frame);
+    }
+
+    /* apply alpha filtering */
+    if (s->alpha_filter)
+        alpha_inverse_prediction(p, s->alpha_filter);
+
+    return 0;
+}
+
+static int vp8_lossy_decode_frame(AVCodecContext *avctx, AVFrame *p,
+                                  int *got_frame, uint8_t *data_start,
+                                  unsigned int data_size)
+{
+    WebPContext *s = avctx->priv_data;
+    AVPacket pkt;
+    int ret;
+
+    if (!s->initialized) {
+        ff_vp8_decode_init(avctx);
+        s->initialized = 1;
+        if (s->has_alpha)
+            avctx->pix_fmt = AV_PIX_FMT_YUVA420P;
+    }
+    s->lossless = 0;
+
+    if (data_size > INT_MAX) {
+        av_log(avctx, AV_LOG_ERROR, "unsupported chunk size\n");
+        return AVERROR_PATCHWELCOME;
+    }
+
+    av_init_packet(&pkt);
+    pkt.data = data_start;
+    pkt.size = data_size;
+
+    ret = ff_vp8_decode_frame(avctx, p, got_frame, &pkt);
+    if (s->has_alpha) {
+        ret = vp8_lossy_decode_alpha(avctx, p, s->alpha_data,
+                                     s->alpha_data_size);
+        if (ret < 0)
+            return ret;
+    }
+    return ret;
+}
+
+static int webp_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
+                             AVPacket *avpkt)
+{
+    AVFrame * const p = data;
+    WebPContext *s = avctx->priv_data;
+    GetByteContext gb;
+    int ret;
+    uint32_t chunk_type, chunk_size;
+    int vp8x_flags = 0;
+
+    s->avctx     = avctx;
+    s->width     = 0;
+    s->height    = 0;
+    *got_frame   = 0;
+    s->has_alpha = 0;
+    bytestream2_init(&gb, avpkt->data, avpkt->size);
+
+    if (bytestream2_get_bytes_left(&gb) < 12)
+        return AVERROR_INVALIDDATA;
+
+    if (bytestream2_get_le32(&gb) != MKTAG('R', 'I', 'F', 'F')) {
+        av_log(avctx, AV_LOG_ERROR, "missing RIFF tag\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    chunk_size = bytestream2_get_le32(&gb);
+    if (bytestream2_get_bytes_left(&gb) < chunk_size)
+        return AVERROR_INVALIDDATA;
+
+    if (bytestream2_get_le32(&gb) != MKTAG('W', 'E', 'B', 'P')) {
+        av_log(avctx, AV_LOG_ERROR, "missing WEBP tag\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    while (bytestream2_get_bytes_left(&gb) > 0) {
+        char chunk_str[5] = { 0 };
+
+        chunk_type = bytestream2_get_le32(&gb);
+        chunk_size = bytestream2_get_le32(&gb);
+        if (chunk_size == UINT32_MAX)
+            return AVERROR_INVALIDDATA;
+        chunk_size += chunk_size & 1;
+
+        if (bytestream2_get_bytes_left(&gb) < chunk_size)
+            return AVERROR_INVALIDDATA;
+
+        switch (chunk_type) {
+        case MKTAG('V', 'P', '8', ' '):
+            if (!*got_frame) {
+                ret = vp8_lossy_decode_frame(avctx, p, got_frame,
+                                             avpkt->data + bytestream2_tell(&gb),
+                                             chunk_size);
+                if (ret < 0)
+                    return ret;
+            }
+            bytestream2_skip(&gb, chunk_size);
+            break;
+        case MKTAG('V', 'P', '8', 'L'):
+            if (!*got_frame) {
+                ret = vp8_lossless_decode_frame(avctx, p, got_frame,
+                                                avpkt->data + bytestream2_tell(&gb),
+                                                chunk_size, 0);
+                if (ret < 0)
+                    return ret;
+            }
+            bytestream2_skip(&gb, chunk_size);
+            break;
+        case MKTAG('V', 'P', '8', 'X'):
+            vp8x_flags = bytestream2_get_byte(&gb);
+            bytestream2_skip(&gb, 3);
+            s->width  = bytestream2_get_le24(&gb) + 1;
+            s->height = bytestream2_get_le24(&gb) + 1;
+            ret = av_image_check_size(s->width, s->height, 0, avctx);
+            if (ret < 0)
+                return ret;
+            break;
+        case MKTAG('A', 'L', 'P', 'H'): {
+            int alpha_header, filter_m, compression;
+
+            if (!(vp8x_flags & VP8X_FLAG_ALPHA)) {
+                av_log(avctx, AV_LOG_WARNING,
+                       "ALPHA chunk present, but alpha bit not set in the "
+                       "VP8X header\n");
+            }
+            if (chunk_size == 0) {
+                av_log(avctx, AV_LOG_ERROR, "invalid ALPHA chunk size\n");
+                return AVERROR_INVALIDDATA;
+            }
+            alpha_header       = bytestream2_get_byte(&gb);
+            s->alpha_data      = avpkt->data + bytestream2_tell(&gb);
+            s->alpha_data_size = chunk_size - 1;
+            bytestream2_skip(&gb, s->alpha_data_size);
+
+            filter_m    = (alpha_header >> 2) & 0x03;
+            compression =  alpha_header       & 0x03;
+
+            if (compression > ALPHA_COMPRESSION_VP8L) {
+                av_log(avctx, AV_LOG_VERBOSE,
+                       "skipping unsupported ALPHA chunk\n");
+            } else {
+                s->has_alpha         = 1;
+                s->alpha_compression = compression;
+                s->alpha_filter      = filter_m;
+            }
+
+            break;
+        }
+        case MKTAG('I', 'C', 'C', 'P'):
+        case MKTAG('A', 'N', 'I', 'M'):
+        case MKTAG('A', 'N', 'M', 'F'):
+        case MKTAG('E', 'X', 'I', 'F'):
+        case MKTAG('X', 'M', 'P', ' '):
+            AV_WL32(chunk_str, chunk_type);
+            av_log(avctx, AV_LOG_VERBOSE, "skipping unsupported chunk: %s\n",
+                   chunk_str);
+            bytestream2_skip(&gb, chunk_size);
+            break;
+        default:
+            AV_WL32(chunk_str, chunk_type);
+            av_log(avctx, AV_LOG_VERBOSE, "skipping unknown chunk: %s\n",
+                   chunk_str);
+            bytestream2_skip(&gb, chunk_size);
+            break;
+        }
+    }
+
+    if (!*got_frame) {
+        av_log(avctx, AV_LOG_ERROR, "image data not found\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    return avpkt->size;
+}
+
+static av_cold int webp_decode_close(AVCodecContext *avctx)
+{
+    WebPContext *s = avctx->priv_data;
+
+    if (s->initialized)
+        return ff_vp8_decode_free(avctx);
+
+    return 0;
+}
+
+AVCodec ff_webp_decoder = {
+    .name           = "webp",
+    .long_name      = NULL_IF_CONFIG_SMALL("WebP image"),
+    .type           = AVMEDIA_TYPE_VIDEO,
+    .id             = AV_CODEC_ID_WEBP,
+    .priv_data_size = sizeof(WebPContext),
+    .decode         = webp_decode_frame,
+    .close          = webp_decode_close,
+    .capabilities   = CODEC_CAP_DR1 | CODEC_CAP_FRAME_THREADS,
+};