libwebp/examples/gif2webp.c

// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
//  simple tool to convert animated GIFs to WebP
//
// Authors: Skal (pascal.massimino@gmail.com)
//          Urvang (urvang@google.com)

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef HAVE_CONFIG_H
#include "webp/config.h"
#endif

#ifdef WEBP_HAVE_GIF

#include <gif_lib.h>
#include "webp/encode.h"
#include "webp/mux.h"
#include "./example_util.h"

// GIFLIB_MAJOR is only defined in libgif >= 4.2.0.
#if defined(GIFLIB_MAJOR) && defined(GIFLIB_MINOR)
# define LOCAL_GIF_VERSION ((GIFLIB_MAJOR << 8) | GIFLIB_MINOR)
# define LOCAL_GIF_PREREQ(maj, min) \
    (LOCAL_GIF_VERSION >= (((maj) << 8) | (min)))
#else
# define LOCAL_GIF_VERSION 0
# define LOCAL_GIF_PREREQ(maj, min) 0
#endif

#define GIF_TRANSPARENT_MASK 0x01
#define GIF_DISPOSE_MASK     0x07
#define GIF_DISPOSE_SHIFT    2
#define WHITE_COLOR          0xffffffff
#define TRANSPARENT_COLOR    0x00ffffff
#define MAX_CACHE_SIZE       30

typedef enum GIFDisposeMethod {
  GIF_DISPOSE_NONE,
  GIF_DISPOSE_BACKGROUND,
  GIF_DISPOSE_RESTORE_PREVIOUS
} GIFDisposeMethod;

typedef struct {
  int x_offset, y_offset, width, height;
} GIFFrameRect;

//------------------------------------------------------------------------------

static int transparent_index = -1;  // Opaque frame by default.

static void ClearRectangle(WebPPicture* const picture,
                           int left, int top, int width, int height) {
  int j;
  for (j = top; j < top + height; ++j) {
    uint32_t* const dst = picture->argb + j * picture->argb_stride;
    int i;
    for (i = left; i < left + width; ++i) {
      dst[i] = TRANSPARENT_COLOR;
    }
  }
}

static void ClearPic(WebPPicture* const pic, const GIFFrameRect* const rect) {
  if (rect != NULL) {
    ClearRectangle(pic, rect->x_offset, rect->y_offset,
                   rect->width, rect->height);
  } else {
    ClearRectangle(pic, 0, 0, pic->width, pic->height);
  }
}

// TODO: Also used in picture.c. Move to a common location?
// Copy width x height pixels from 'src' to 'dst' honoring the strides.
static void CopyPlane(const uint8_t* src, int src_stride,
                      uint8_t* dst, int dst_stride, int width, int height) {
  while (height-- > 0) {
    memcpy(dst, src, width);
    src += src_stride;
    dst += dst_stride;
  }
}

// Copy pixels from 'src' to 'dst' honoring strides. 'src' and 'dst' are assumed
// to be already allocated.
static void CopyPixels(const WebPPicture* const src, WebPPicture* const dst) {
  assert(src->width == dst->width && src->height == dst->height);
  CopyPlane((uint8_t*)src->argb, 4 * src->argb_stride, (uint8_t*)dst->argb,
            4 * dst->argb_stride, 4 * src->width, src->height);
}

// Given 'src' picture and its frame rectangle 'rect', blend it into 'dst'.
static void BlendPixels(const WebPPicture* const src,
                        const GIFFrameRect* const rect,
                        WebPPicture* const dst) {
  int j;
  assert(src->width == dst->width && src->height == dst->height);
  for (j = rect->y_offset; j < rect->y_offset + rect->height; ++j) {
    int i;
    for (i = rect->x_offset; i < rect->x_offset + rect->width; ++i) {
      const uint32_t src_pixel = src->argb[j * src->argb_stride + i];
      const int src_alpha = src_pixel >> 24;
      if (src_alpha != 0) {
        dst->argb[j * dst->argb_stride + i] = src_pixel;
      }
    }
  }
}

static void DisposeFrameRectangle(GIFDisposeMethod dispose_method,
                                  const GIFFrameRect* const rect,
                                  const WebPPicture* const prev_canvas,
                                  WebPPicture* const curr_canvas) {
  assert(rect != NULL);
  if (dispose_method == GIF_DISPOSE_BACKGROUND) {
    ClearPic(curr_canvas, rect);
  } else if (dispose_method == GIF_DISPOSE_RESTORE_PREVIOUS) {
    const int src_stride = prev_canvas->argb_stride;
    const uint32_t* const src =
        prev_canvas->argb + rect->x_offset + rect->y_offset * src_stride;
    const int dst_stride = curr_canvas->argb_stride;
    uint32_t* const dst =
        curr_canvas->argb + rect->x_offset + rect->y_offset * dst_stride;
    assert(prev_canvas != NULL);
    CopyPlane((uint8_t*)src, 4 * src_stride, (uint8_t*)dst, 4 * dst_stride,
              4 * rect->width, rect->height);
  }
}

static void Remap(const uint8_t* const src, const GifFileType* const gif,
                  uint32_t* dst, int len) {
  int i;
  const GifColorType* colors;
  const ColorMapObject* const cmap =
      gif->Image.ColorMap ? gif->Image.ColorMap : gif->SColorMap;
  if (cmap == NULL) return;
  colors = cmap->Colors;

  for (i = 0; i < len; ++i) {
    const GifColorType c = colors[src[i]];
    dst[i] = (src[i] == transparent_index) ? TRANSPARENT_COLOR
           : c.Blue | (c.Green << 8) | (c.Red << 16) | (0xff << 24);
  }
}

// Read the GIF image frame.
static int ReadFrame(GifFileType* const gif, GIFFrameRect* const gif_rect,
                     WebPPicture* const webp_frame) {
  WebPPicture sub_image;
  const GifImageDesc* const image_desc = &gif->Image;
  uint32_t* dst = NULL;
  uint8_t* tmp = NULL;
  int ok = 0;
  GIFFrameRect rect = {
      image_desc->Left, image_desc->Top, image_desc->Width, image_desc->Height
  };
  *gif_rect = rect;

  // Use a view for the sub-picture:
  if (!WebPPictureView(webp_frame, rect.x_offset, rect.y_offset,
                       rect.width, rect.height, &sub_image)) {
    fprintf(stderr, "Sub-image %dx%d at position %d,%d is invalid!\n",
            rect.width, rect.height, rect.x_offset, rect.y_offset);
    return 0;
  }
  dst = sub_image.argb;

  tmp = (uint8_t*)malloc(rect.width * sizeof(*tmp));
  if (tmp == NULL) goto End;

  if (image_desc->Interlace) {  // Interlaced image.
    // We need 4 passes, with the following offsets and jumps.
    const int interlace_offsets[] = { 0, 4, 2, 1 };
    const int interlace_jumps[]   = { 8, 8, 4, 2 };
    int pass;
    for (pass = 0; pass < 4; ++pass) {
      int y;
      for (y = interlace_offsets[pass]; y < rect.height;
           y += interlace_jumps[pass]) {
        if (DGifGetLine(gif, tmp, rect.width) == GIF_ERROR) goto End;
        Remap(tmp, gif, dst + y * sub_image.argb_stride, rect.width);
      }
    }
  } else {  // Non-interlaced image.
    int y;
    for (y = 0; y < rect.height; ++y) {
      if (DGifGetLine(gif, tmp, rect.width) == GIF_ERROR) goto End;
      Remap(tmp, gif, dst + y * sub_image.argb_stride, rect.width);
    }
  }
  ok = 1;

 End:
  if (!ok) webp_frame->error_code = sub_image.error_code;
  WebPPictureFree(&sub_image);
  free(tmp);
  return ok;
}

static void GetBackgroundColor(const ColorMapObject* const color_map,
                               int bgcolor_idx, uint32_t* const bgcolor) {
  if (transparent_index != -1 && bgcolor_idx == transparent_index) {
    *bgcolor = TRANSPARENT_COLOR;  // Special case.
  } else if (color_map == NULL || color_map->Colors == NULL
             || bgcolor_idx >= color_map->ColorCount) {
    *bgcolor = WHITE_COLOR;
    fprintf(stderr,
            "GIF decode warning: invalid background color index. Assuming "
            "white background.\n");
  } else {
    const GifColorType color = color_map->Colors[bgcolor_idx];
    *bgcolor = (0xff        << 24)
             | (color.Red   << 16)
             | (color.Green <<  8)
             | (color.Blue  <<  0);
  }
}

static void DisplayGifError(const GifFileType* const gif, int gif_error) {
  // libgif 4.2.0 has retired PrintGifError() and added GifErrorString().
#if LOCAL_GIF_PREREQ(4,2)
#if LOCAL_GIF_PREREQ(5,0)
  // Static string actually, hence the const char* cast.
  const char* error_str = (const char*)GifErrorString(
      (gif == NULL) ? gif_error : gif->Error);
#else
  const char* error_str = (const char*)GifErrorString();
  (void)gif;
#endif
  if (error_str == NULL) error_str = "Unknown error";
  fprintf(stderr, "GIFLib Error %d: %s\n", gif_error, error_str);
#else
  (void)gif;
  fprintf(stderr, "GIFLib Error %d: ", gif_error);
  PrintGifError();
  fprintf(stderr, "\n");
#endif
}

static const char* const kErrorMessages[-WEBP_MUX_NOT_ENOUGH_DATA + 1] = {
  "WEBP_MUX_NOT_FOUND", "WEBP_MUX_INVALID_ARGUMENT", "WEBP_MUX_BAD_DATA",
  "WEBP_MUX_MEMORY_ERROR", "WEBP_MUX_NOT_ENOUGH_DATA"
};

static const char* ErrorString(WebPMuxError err) {
  assert(err <= WEBP_MUX_NOT_FOUND && err >= WEBP_MUX_NOT_ENOUGH_DATA);
  return kErrorMessages[-err];
}

enum {
  METADATA_ICC  = (1 << 0),
  METADATA_XMP  = (1 << 1),
  METADATA_ALL  = METADATA_ICC | METADATA_XMP
};

//------------------------------------------------------------------------------

static void Help(void) {
  printf("Usage:\n");
  printf(" gif2webp [options] gif_file -o webp_file\n");
  printf("Options:\n");
  printf("  -h / -help  ............ this help\n");
  printf("  -lossy ................. encode image using lossy compression\n");
  printf("  -mixed ................. for each frame in the image, pick lossy\n"
         "                           or lossless compression heuristically\n");
  printf("  -q <float> ............. quality factor (0:small..100:big)\n");
  printf("  -m <int> ............... compression method (0=fast, 6=slowest)\n");
  printf("  -min_size .............. minimize output size (default:off)\n"
         "                           lossless compression by default; can be\n"
         "                           combined with -q, -m, -lossy or -mixed\n"
         "                           options\n");
  printf("  -kmin <int> ............ min distance between key frames\n");
  printf("  -kmax <int> ............ max distance between key frames\n");
  printf("  -f <int> ............... filter strength (0=off..100)\n");
  printf("  -metadata <string> ..... comma separated list of metadata to\n");
  printf("                           ");
  printf("copy from the input to the output if present\n");
  printf("                           "
         "Valid values: all, none, icc, xmp (default)\n");
  printf("  -mt .................... use multi-threading if available\n");
  printf("\n");
  printf("  -version ............... print version number and exit\n");
  printf("  -v ..................... verbose\n");
  printf("  -quiet ................. don't print anything\n");
  printf("\n");
}

//------------------------------------------------------------------------------

int main(int argc, const char *argv[]) {
  int verbose = 0;
  int gif_error = GIF_ERROR;
  WebPMuxError err = WEBP_MUX_OK;
  int ok = 0;
  const char *in_file = NULL, *out_file = NULL;
  FILE* out = NULL;
  GifFileType* gif = NULL;
  int duration = 0;
  GIFDisposeMethod orig_dispose = GIF_DISPOSE_NONE;

  WebPPicture frame;                // Frame rectangle only (not disposed).
  WebPPicture curr_canvas;          // Not disposed.
  WebPPicture prev_canvas;          // Disposed.
  WebPPicture prev_to_prev_canvas;  // Disposed.

  WebPAnimEncoder* enc = NULL;
  WebPAnimEncoderOptions enc_options;
  WebPConfig config;

  int is_first_frame = 1;     // Whether we are processing the first frame.
  int done;
  int c;
  int quiet = 0;
  WebPData webp_data;

  int keep_metadata = METADATA_XMP;  // ICC not output by default.
  WebPData icc_data;
  int stored_icc = 0;         // Whether we have already stored an ICC profile.
  WebPData xmp_data;
  int stored_xmp = 0;         // Whether we have already stored an XMP profile.
  int loop_count = 0;
  int stored_loop_count = 0;  // Whether we have found an explicit loop count.
  WebPMux* mux = NULL;

  int default_kmin = 1;  // Whether to use default kmin value.
  int default_kmax = 1;

  if (!WebPConfigInit(&config) || !WebPAnimEncoderOptionsInit(&enc_options) ||
      !WebPPictureInit(&frame) || !WebPPictureInit(&curr_canvas) ||
      !WebPPictureInit(&prev_canvas) ||
      !WebPPictureInit(&prev_to_prev_canvas)) {
    fprintf(stderr, "Error! Version mismatch!\n");
    return -1;
  }
  config.lossless = 1;  // Use lossless compression by default.

  WebPDataInit(&webp_data);
  WebPDataInit(&icc_data);
  WebPDataInit(&xmp_data);

  if (argc == 1) {
    Help();
    return 0;
  }

  for (c = 1; c < argc; ++c) {
    int parse_error = 0;
    if (!strcmp(argv[c], "-h") || !strcmp(argv[c], "-help")) {
      Help();
      return 0;
    } else if (!strcmp(argv[c], "-o") && c < argc - 1) {
      out_file = argv[++c];
    } else if (!strcmp(argv[c], "-lossy")) {
      config.lossless = 0;
    } else if (!strcmp(argv[c], "-mixed")) {
      enc_options.allow_mixed = 1;
      config.lossless = 0;
    } else if (!strcmp(argv[c], "-q") && c < argc - 1) {
      config.quality = ExUtilGetFloat(argv[++c], &parse_error);
    } else if (!strcmp(argv[c], "-m") && c < argc - 1) {
      config.method = ExUtilGetInt(argv[++c], 0, &parse_error);
    } else if (!strcmp(argv[c], "-min_size")) {
      enc_options.minimize_size = 1;
    } else if (!strcmp(argv[c], "-kmax") && c < argc - 1) {
      enc_options.kmax = ExUtilGetUInt(argv[++c], 0, &parse_error);
      default_kmax = 0;
    } else if (!strcmp(argv[c], "-kmin") && c < argc - 1) {
      enc_options.kmin = ExUtilGetUInt(argv[++c], 0, &parse_error);
      default_kmin = 0;
    } else if (!strcmp(argv[c], "-f") && c < argc - 1) {
      config.filter_strength = ExUtilGetInt(argv[++c], 0, &parse_error);
    } else if (!strcmp(argv[c], "-metadata") && c < argc - 1) {
      static const struct {
        const char* option;
        int flag;
      } kTokens[] = {
        { "all",  METADATA_ALL },
        { "none", 0 },
        { "icc",  METADATA_ICC },
        { "xmp",  METADATA_XMP },
      };
      const size_t kNumTokens = sizeof(kTokens) / sizeof(*kTokens);
      const char* start = argv[++c];
      const char* const end = start + strlen(start);

      keep_metadata = 0;
      while (start < end) {
        size_t i;
        const char* token = strchr(start, ',');
        if (token == NULL) token = end;

        for (i = 0; i < kNumTokens; ++i) {
          if ((size_t)(token - start) == strlen(kTokens[i].option) &&
              !strncmp(start, kTokens[i].option, strlen(kTokens[i].option))) {
            if (kTokens[i].flag != 0) {
              keep_metadata |= kTokens[i].flag;
            } else {
              keep_metadata = 0;
            }
            break;
          }
        }
        if (i == kNumTokens) {
          fprintf(stderr, "Error! Unknown metadata type '%.*s'\n",
                  (int)(token - start), start);
          Help();
          return -1;
        }
        start = token + 1;
      }
    } else if (!strcmp(argv[c], "-mt")) {
      ++config.thread_level;
    } else if (!strcmp(argv[c], "-version")) {
      const int enc_version = WebPGetEncoderVersion();
      const int mux_version = WebPGetMuxVersion();
      printf("WebP Encoder version: %d.%d.%d\nWebP Mux version: %d.%d.%d\n",
             (enc_version >> 16) & 0xff, (enc_version >> 8) & 0xff,
             enc_version & 0xff, (mux_version >> 16) & 0xff,
             (mux_version >> 8) & 0xff, mux_version & 0xff);
      return 0;
    } else if (!strcmp(argv[c], "-quiet")) {
      quiet = 1;
    } else if (!strcmp(argv[c], "-v")) {
      verbose = 1;
      enc_options.verbose = 1;
    } else if (!strcmp(argv[c], "--")) {
      if (c < argc - 1) in_file = argv[++c];
      break;
    } else if (argv[c][0] == '-') {
      fprintf(stderr, "Error! Unknown option '%s'\n", argv[c]);
      Help();
      return -1;
    } else {
      in_file = argv[c];
    }

    if (parse_error) {
      Help();
      return -1;
    }
  }

  // Appropriate default kmin, kmax values for lossy and lossless.
  if (default_kmin) {
    enc_options.kmin = config.lossless ? 9 : 3;
  }
  if (default_kmax) {
    enc_options.kmax = config.lossless ? 17 : 5;
  }

  if (!WebPValidateConfig(&config)) {
    fprintf(stderr, "Error! Invalid configuration.\n");
    goto End;
  }

  if (in_file == NULL) {
    fprintf(stderr, "No input file specified!\n");
    Help();
    goto End;
  }

  // Start the decoder object
#if LOCAL_GIF_PREREQ(5,0)
  gif = DGifOpenFileName(in_file, &gif_error);
#else
  gif = DGifOpenFileName(in_file);
#endif
  if (gif == NULL) goto End;

  // Loop over GIF images
  done = 0;
  do {
    GifRecordType type;
    if (DGifGetRecordType(gif, &type) == GIF_ERROR) goto End;

    switch (type) {
      case IMAGE_DESC_RECORD_TYPE: {
        GIFFrameRect gif_rect;
        GifImageDesc* const image_desc = &gif->Image;

        if (!DGifGetImageDesc(gif)) goto End;

        if (is_first_frame) {
          if (verbose) {
            printf("Canvas screen: %d x %d\n", gif->SWidth, gif->SHeight);
          }
          // Fix some broken GIF global headers that report
          // 0 x 0 screen dimension.
          if (gif->SWidth == 0 || gif->SHeight == 0) {
            image_desc->Left = 0;
            image_desc->Top = 0;
            gif->SWidth = image_desc->Width;
            gif->SHeight = image_desc->Height;
            if (gif->SWidth <= 0 || gif->SHeight <= 0) {
              goto End;
            }
            if (verbose) {
              printf("Fixed canvas screen dimension to: %d x %d\n",
                     gif->SWidth, gif->SHeight);
            }
          }
          // Allocate current buffer.
          frame.width = gif->SWidth;
          frame.height = gif->SHeight;
          frame.use_argb = 1;
          if (!WebPPictureAlloc(&frame)) goto End;
          ClearPic(&frame, NULL);
          WebPPictureCopy(&frame, &curr_canvas);
          WebPPictureCopy(&frame, &prev_canvas);
          WebPPictureCopy(&frame, &prev_to_prev_canvas);

          // Background color.
          GetBackgroundColor(gif->SColorMap, gif->SBackGroundColor,
                             &enc_options.anim_params.bgcolor);

          // Initialize encoder.
          enc = WebPAnimEncoderNew(curr_canvas.width, curr_canvas.height,
                                   &enc_options);
          if (enc == NULL) goto End;
          is_first_frame = 0;
        }

        // Some even more broken GIF can have sub-rect with zero width/height.
        if (image_desc->Width == 0 || image_desc->Height == 0) {
          image_desc->Width = gif->SWidth;
          image_desc->Height = gif->SHeight;
        }

        if (!ReadFrame(gif, &gif_rect, &frame)) {
          goto End;
        }
        // Blend frame rectangle with previous canvas to compose full canvas.
        // Note that 'curr_canvas' is same as 'prev_canvas' at this point.
        BlendPixels(&frame, &gif_rect, &curr_canvas);

        if (!WebPAnimEncoderAdd(enc, &curr_canvas, duration, &config)) {
          fprintf(stderr, "Error! Cannot encode frame as WebP\n");
          fprintf(stderr, "Error code: %d\n", curr_canvas.error_code);
        }

        // Update canvases.
        CopyPixels(&prev_canvas, &prev_to_prev_canvas);
        DisposeFrameRectangle(orig_dispose, &gif_rect, &prev_canvas,
                              &curr_canvas);
        CopyPixels(&curr_canvas, &prev_canvas);

        // In GIF, graphic control extensions are optional for a frame, so we
        // may not get one before reading the next frame. To handle this case,
        // we reset frame properties to reasonable defaults for the next frame.
        orig_dispose = GIF_DISPOSE_NONE;
        duration = 0;
        transparent_index = -1;  // Opaque frame by default.
        break;
      }
      case EXTENSION_RECORD_TYPE: {
        int extension;
        GifByteType *data = NULL;
        if (DGifGetExtension(gif, &extension, &data) == GIF_ERROR) {
          goto End;
        }
        switch (extension) {
          case COMMENT_EXT_FUNC_CODE: {
            break;  // Do nothing for now.
          }
          case GRAPHICS_EXT_FUNC_CODE: {
            const int flags = data[1];
            const int dispose = (flags >> GIF_DISPOSE_SHIFT) & GIF_DISPOSE_MASK;
            const int delay = data[2] | (data[3] << 8);  // In 10 ms units.
            if (data[0] != 4) goto End;
            duration = delay * 10;  // Duration is in 1 ms units for WebP.
            switch (dispose) {
              case 3:
                orig_dispose = GIF_DISPOSE_RESTORE_PREVIOUS;
                break;
              case 2:
                orig_dispose = GIF_DISPOSE_BACKGROUND;
                break;
              case 1:
              case 0:
              default:
                orig_dispose = GIF_DISPOSE_NONE;
                break;
            }
            transparent_index = (flags & GIF_TRANSPARENT_MASK) ? data[4] : -1;
            break;
          }
          case PLAINTEXT_EXT_FUNC_CODE: {
            break;
          }
          case APPLICATION_EXT_FUNC_CODE: {
            if (data[0] != 11) break;    // Chunk is too short
            if (!memcmp(data + 1, "NETSCAPE2.0", 11) ||
                !memcmp(data + 1, "ANIMEXTS1.0", 11)) {
              // Recognize and parse Netscape2.0 NAB extension for loop count.
              if (DGifGetExtensionNext(gif, &data) == GIF_ERROR) goto End;
              if (data == NULL) goto End;  // Loop count sub-block missing.
              if (data[0] < 3 || data[1] != 1) break;   // wrong size/marker
              loop_count = data[2] | (data[3] << 8);
              if (verbose) {
                fprintf(stderr, "Loop count: %d\n", loop_count);
              }
              stored_loop_count = (loop_count != 0);
            } else {  // An extension containing metadata.
              // We only store the first encountered chunk of each type, and
              // only if requested by the user.
              const int is_xmp = (keep_metadata & METADATA_XMP) &&
                                 !stored_xmp &&
                                 !memcmp(data + 1, "XMP DataXMP", 11);
              const int is_icc = (keep_metadata & METADATA_ICC) &&
                                 !stored_icc &&
                                 !memcmp(data + 1, "ICCRGBG1012", 11);
              if (is_xmp || is_icc) {
                WebPData* const metadata = is_xmp ? &xmp_data : &icc_data;
                // Construct metadata from sub-blocks.
                // Usual case (including ICC profile): In each sub-block, the
                // first byte specifies its size in bytes (0 to 255) and the
                // rest of the bytes contain the data.
                // Special case for XMP data: In each sub-block, the first byte
                // is also part of the XMP payload. XMP in GIF also has a 257
                // byte padding data. See the XMP specification for details.
                while (1) {
                  WebPData subblock;
                  const uint8_t* tmp;
                  if (DGifGetExtensionNext(gif, &data) == GIF_ERROR) {
                    goto End;
                  }
                  if (data == NULL) break;  // Finished.
                  subblock.size = is_xmp ? data[0] + 1 : data[0];
                  assert(subblock.size > 0);
                  subblock.bytes = is_xmp ? data : data + 1;
                  // Note: We store returned value in 'tmp' first, to avoid
                  // leaking old memory in metadata->bytes on error.
                  tmp = (uint8_t*)realloc((void*)metadata->bytes,
                                          metadata->size + subblock.size);
                  if (tmp == NULL) {
                    goto End;
                  }
                  memcpy((void*)(tmp + metadata->size),
                         subblock.bytes, subblock.size);
                  metadata->bytes = tmp;
                  metadata->size += subblock.size;
                }
                if (is_xmp) {
                  // XMP padding data is 0x01, 0xff, 0xfe ... 0x01, 0x00.
                  const size_t xmp_pading_size = 257;
                  if (metadata->size > xmp_pading_size) {
                    metadata->size -= xmp_pading_size;
                  }
                }
                if (is_icc) {
                  stored_icc = 1;
                } else if (is_xmp) {
                  stored_xmp = 1;
                }
              }
            }
            break;
          }
          default: {
            break;  // skip
          }
        }
        while (data != NULL) {
          if (DGifGetExtensionNext(gif, &data) == GIF_ERROR) goto End;
        }
        break;
      }
      case TERMINATE_RECORD_TYPE: {
        done = 1;
        break;
      }
      default: {
        if (verbose) {
          fprintf(stderr, "Skipping over unknown record type %d\n", type);
        }
        break;
      }
    }
  } while (!done);

  if (!WebPAnimEncoderAssemble(enc, &webp_data)) {
    // TODO(urvang): Print actual error code.
    fprintf(stderr, "ERROR assembling the WebP file.\n");
    goto End;
  }

  if (stored_loop_count || stored_icc || stored_xmp) {
    // Re-mux to add loop count and/or metadata as needed.
    mux = WebPMuxCreate(&webp_data, 1);
    if (mux == NULL) {
      fprintf(stderr, "ERROR: Could not re-mux to add loop count/metadata.\n");
      goto End;
    }
    WebPDataClear(&webp_data);

    if (stored_loop_count) {  // Update loop count.
      WebPMuxAnimParams new_params;
      err = WebPMuxGetAnimationParams(mux, &new_params);
      if (err != WEBP_MUX_OK) {
        fprintf(stderr, "ERROR (%s): Could not fetch loop count.\n",
                ErrorString(err));
        goto End;
      }
      new_params.loop_count = loop_count;
      err = WebPMuxSetAnimationParams(mux, &new_params);
      if (err != WEBP_MUX_OK) {
        fprintf(stderr, "ERROR (%s): Could not update loop count.\n",
                ErrorString(err));
        goto End;
      }
    }

    if (stored_icc) {   // Add ICCP chunk.
      err = WebPMuxSetChunk(mux, "ICCP", &icc_data, 1);
      if (verbose) {
        fprintf(stderr, "ICC size: %d\n", (int)icc_data.size);
      }
      if (err != WEBP_MUX_OK) {
        fprintf(stderr, "ERROR (%s): Could not set ICC chunk.\n",
                ErrorString(err));
        goto End;
      }
    }

    if (stored_xmp) {   // Add XMP chunk.
      err = WebPMuxSetChunk(mux, "XMP ", &xmp_data, 1);
      if (verbose) {
        fprintf(stderr, "XMP size: %d\n", (int)xmp_data.size);
      }
      if (err != WEBP_MUX_OK) {
        fprintf(stderr, "ERROR (%s): Could not set XMP chunk.\n",
                ErrorString(err));
        goto End;
      }
    }

    err = WebPMuxAssemble(mux, &webp_data);
    if (err != WEBP_MUX_OK) {
      fprintf(stderr, "ERROR (%s): Could not assemble when re-muxing to add "
              "loop count/metadata.\n", ErrorString(err));
      goto End;
    }
  }

  if (out_file != NULL) {
    if (!ExUtilWriteFile(out_file, webp_data.bytes, webp_data.size)) {
      fprintf(stderr, "Error writing output file: %s\n", out_file);
      goto End;
    }
    if (!quiet) {
      fprintf(stderr, "Saved output file: %s\n", out_file);
    }
  } else {
    if (!quiet) {
      fprintf(stderr, "Nothing written; use -o flag to save the result.\n");
    }
  }

  // All OK.
  ok = 1;
  gif_error = GIF_OK;

 End:
  WebPDataClear(&icc_data);
  WebPDataClear(&xmp_data);
  WebPMuxDelete(mux);
  WebPDataClear(&webp_data);
  WebPPictureFree(&frame);
  WebPPictureFree(&curr_canvas);
  WebPPictureFree(&prev_canvas);
  WebPPictureFree(&prev_to_prev_canvas);
  WebPAnimEncoderDelete(enc);
  if (out != NULL && out_file != NULL) fclose(out);

  if (gif_error != GIF_OK) {
    DisplayGifError(gif, gif_error);
  }
  if (gif != NULL) {
#if LOCAL_GIF_PREREQ(5,1)
    DGifCloseFile(gif, &gif_error);
#else
    DGifCloseFile(gif);
#endif
  }

  return !ok;
}

#else  // !WEBP_HAVE_GIF

int main(int argc, const char *argv[]) {
  fprintf(stderr, "GIF support not enabled in %s.\n", argv[0]);
  (void)argc;
  return 0;
}

#endif

//------------------------------------------------------------------------------