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      1 // Copyright 2011 Google Inc. All Rights Reserved.
      2 //
      3 // Use of this source code is governed by a BSD-style license
      4 // that can be found in the COPYING file in the root of the source
      5 // tree. An additional intellectual property rights grant can be found
      6 // in the file PATENTS. All contributing project authors may
      7 // be found in the AUTHORS file in the root of the source tree.
      8 // -----------------------------------------------------------------------------
      9 //
     10 // Read APIs for mux.
     11 //
     12 // Authors: Urvang (urvang (at) google.com)
     13 //          Vikas (vikasa (at) google.com)
     14 
     15 #include <assert.h>
     16 #include "src/mux/muxi.h"
     17 #include "src/utils/utils.h"
     18 
     19 //------------------------------------------------------------------------------
     20 // Helper method(s).
     21 
     22 // Handy MACRO.
     23 #define SWITCH_ID_LIST(INDEX, LIST)                                           \
     24   if (idx == (INDEX)) {                                                       \
     25     const WebPChunk* const chunk = ChunkSearchList((LIST), nth,               \
     26                                                    kChunks[(INDEX)].tag);     \
     27     if (chunk) {                                                              \
     28       *data = chunk->data_;                                                   \
     29       return WEBP_MUX_OK;                                                     \
     30     } else {                                                                  \
     31       return WEBP_MUX_NOT_FOUND;                                              \
     32     }                                                                         \
     33   }
     34 
     35 static WebPMuxError MuxGet(const WebPMux* const mux, CHUNK_INDEX idx,
     36                            uint32_t nth, WebPData* const data) {
     37   assert(mux != NULL);
     38   assert(!IsWPI(kChunks[idx].id));
     39   WebPDataInit(data);
     40 
     41   SWITCH_ID_LIST(IDX_VP8X, mux->vp8x_);
     42   SWITCH_ID_LIST(IDX_ICCP, mux->iccp_);
     43   SWITCH_ID_LIST(IDX_ANIM, mux->anim_);
     44   SWITCH_ID_LIST(IDX_EXIF, mux->exif_);
     45   SWITCH_ID_LIST(IDX_XMP, mux->xmp_);
     46   assert(idx != IDX_UNKNOWN);
     47   return WEBP_MUX_NOT_FOUND;
     48 }
     49 #undef SWITCH_ID_LIST
     50 
     51 // Fill the chunk with the given data (includes chunk header bytes), after some
     52 // verifications.
     53 static WebPMuxError ChunkVerifyAndAssign(WebPChunk* chunk,
     54                                          const uint8_t* data, size_t data_size,
     55                                          size_t riff_size, int copy_data) {
     56   uint32_t chunk_size;
     57   WebPData chunk_data;
     58 
     59   // Sanity checks.
     60   if (data_size < CHUNK_HEADER_SIZE) return WEBP_MUX_NOT_ENOUGH_DATA;
     61   chunk_size = GetLE32(data + TAG_SIZE);
     62   if (chunk_size > MAX_CHUNK_PAYLOAD) return WEBP_MUX_BAD_DATA;
     63 
     64   {
     65     const size_t chunk_disk_size = SizeWithPadding(chunk_size);
     66     if (chunk_disk_size > riff_size) return WEBP_MUX_BAD_DATA;
     67     if (chunk_disk_size > data_size) return WEBP_MUX_NOT_ENOUGH_DATA;
     68   }
     69 
     70   // Data assignment.
     71   chunk_data.bytes = data + CHUNK_HEADER_SIZE;
     72   chunk_data.size = chunk_size;
     73   return ChunkAssignData(chunk, &chunk_data, copy_data, GetLE32(data + 0));
     74 }
     75 
     76 int MuxImageFinalize(WebPMuxImage* const wpi) {
     77   const WebPChunk* const img = wpi->img_;
     78   const WebPData* const image = &img->data_;
     79   const int is_lossless = (img->tag_ == kChunks[IDX_VP8L].tag);
     80   int w, h;
     81   int vp8l_has_alpha = 0;
     82   const int ok = is_lossless ?
     83       VP8LGetInfo(image->bytes, image->size, &w, &h, &vp8l_has_alpha) :
     84       VP8GetInfo(image->bytes, image->size, image->size, &w, &h);
     85   assert(img != NULL);
     86   if (ok) {
     87     // Ignore ALPH chunk accompanying VP8L.
     88     if (is_lossless && (wpi->alpha_ != NULL)) {
     89       ChunkDelete(wpi->alpha_);
     90       wpi->alpha_ = NULL;
     91     }
     92     wpi->width_ = w;
     93     wpi->height_ = h;
     94     wpi->has_alpha_ = vp8l_has_alpha || (wpi->alpha_ != NULL);
     95   }
     96   return ok;
     97 }
     98 
     99 static int MuxImageParse(const WebPChunk* const chunk, int copy_data,
    100                          WebPMuxImage* const wpi) {
    101   const uint8_t* bytes = chunk->data_.bytes;
    102   size_t size = chunk->data_.size;
    103   const uint8_t* const last = bytes + size;
    104   WebPChunk subchunk;
    105   size_t subchunk_size;
    106   WebPChunk** unknown_chunk_list = &wpi->unknown_;
    107   ChunkInit(&subchunk);
    108 
    109   assert(chunk->tag_ == kChunks[IDX_ANMF].tag);
    110   assert(!wpi->is_partial_);
    111 
    112   // ANMF.
    113   {
    114     const size_t hdr_size = ANMF_CHUNK_SIZE;
    115     const WebPData temp = { bytes, hdr_size };
    116     // Each of ANMF chunk contain a header at the beginning. So, its size should
    117     // be at least 'hdr_size'.
    118     if (size < hdr_size) goto Fail;
    119     ChunkAssignData(&subchunk, &temp, copy_data, chunk->tag_);
    120   }
    121   ChunkSetHead(&subchunk, &wpi->header_);
    122   wpi->is_partial_ = 1;  // Waiting for ALPH and/or VP8/VP8L chunks.
    123 
    124   // Rest of the chunks.
    125   subchunk_size = ChunkDiskSize(&subchunk) - CHUNK_HEADER_SIZE;
    126   bytes += subchunk_size;
    127   size -= subchunk_size;
    128 
    129   while (bytes != last) {
    130     ChunkInit(&subchunk);
    131     if (ChunkVerifyAndAssign(&subchunk, bytes, size, size,
    132                              copy_data) != WEBP_MUX_OK) {
    133       goto Fail;
    134     }
    135     switch (ChunkGetIdFromTag(subchunk.tag_)) {
    136       case WEBP_CHUNK_ALPHA:
    137         if (wpi->alpha_ != NULL) goto Fail;  // Consecutive ALPH chunks.
    138         if (ChunkSetHead(&subchunk, &wpi->alpha_) != WEBP_MUX_OK) goto Fail;
    139         wpi->is_partial_ = 1;  // Waiting for a VP8 chunk.
    140         break;
    141       case WEBP_CHUNK_IMAGE:
    142         if (wpi->img_ != NULL) goto Fail;  // Only 1 image chunk allowed.
    143         if (ChunkSetHead(&subchunk, &wpi->img_) != WEBP_MUX_OK) goto Fail;
    144         if (!MuxImageFinalize(wpi)) goto Fail;
    145         wpi->is_partial_ = 0;  // wpi is completely filled.
    146         break;
    147       case WEBP_CHUNK_UNKNOWN:
    148         if (wpi->is_partial_) {
    149           goto Fail;  // Encountered an unknown chunk
    150                       // before some image chunks.
    151         }
    152         if (ChunkAppend(&subchunk, &unknown_chunk_list) != WEBP_MUX_OK) {
    153           goto Fail;
    154         }
    155         break;
    156       default:
    157         goto Fail;
    158         break;
    159     }
    160     subchunk_size = ChunkDiskSize(&subchunk);
    161     bytes += subchunk_size;
    162     size -= subchunk_size;
    163   }
    164   if (wpi->is_partial_) goto Fail;
    165   return 1;
    166 
    167  Fail:
    168   ChunkRelease(&subchunk);
    169   return 0;
    170 }
    171 
    172 //------------------------------------------------------------------------------
    173 // Create a mux object from WebP-RIFF data.
    174 
    175 WebPMux* WebPMuxCreateInternal(const WebPData* bitstream, int copy_data,
    176                                int version) {
    177   size_t riff_size;
    178   uint32_t tag;
    179   const uint8_t* end;
    180   WebPMux* mux = NULL;
    181   WebPMuxImage* wpi = NULL;
    182   const uint8_t* data;
    183   size_t size;
    184   WebPChunk chunk;
    185   // Stores the end of the chunk lists so that it is faster to append data to
    186   // their ends.
    187   WebPChunk** chunk_list_ends[WEBP_CHUNK_NIL + 1] = { NULL };
    188   ChunkInit(&chunk);
    189 
    190   // Sanity checks.
    191   if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_MUX_ABI_VERSION)) {
    192     return NULL;  // version mismatch
    193   }
    194   if (bitstream == NULL) return NULL;
    195 
    196   data = bitstream->bytes;
    197   size = bitstream->size;
    198 
    199   if (data == NULL) return NULL;
    200   if (size < RIFF_HEADER_SIZE + CHUNK_HEADER_SIZE) return NULL;
    201   if (GetLE32(data + 0) != MKFOURCC('R', 'I', 'F', 'F') ||
    202       GetLE32(data + CHUNK_HEADER_SIZE) != MKFOURCC('W', 'E', 'B', 'P')) {
    203     return NULL;
    204   }
    205 
    206   mux = WebPMuxNew();
    207   if (mux == NULL) return NULL;
    208 
    209   tag = GetLE32(data + RIFF_HEADER_SIZE);
    210   if (tag != kChunks[IDX_VP8].tag &&
    211       tag != kChunks[IDX_VP8L].tag &&
    212       tag != kChunks[IDX_VP8X].tag) {
    213     goto Err;  // First chunk should be VP8, VP8L or VP8X.
    214   }
    215 
    216   riff_size = GetLE32(data + TAG_SIZE);
    217   if (riff_size > MAX_CHUNK_PAYLOAD) goto Err;
    218 
    219   // Note this padding is historical and differs from demux.c which does not
    220   // pad the file size.
    221   riff_size = SizeWithPadding(riff_size);
    222   if (riff_size < CHUNK_HEADER_SIZE) goto Err;
    223   if (riff_size > size) goto Err;
    224   // There's no point in reading past the end of the RIFF chunk.
    225   if (size > riff_size + CHUNK_HEADER_SIZE) {
    226     size = riff_size + CHUNK_HEADER_SIZE;
    227   }
    228 
    229   end = data + size;
    230   data += RIFF_HEADER_SIZE;
    231   size -= RIFF_HEADER_SIZE;
    232 
    233   wpi = (WebPMuxImage*)WebPSafeMalloc(1ULL, sizeof(*wpi));
    234   if (wpi == NULL) goto Err;
    235   MuxImageInit(wpi);
    236 
    237   // Loop over chunks.
    238   while (data != end) {
    239     size_t data_size;
    240     WebPChunkId id;
    241     if (ChunkVerifyAndAssign(&chunk, data, size, riff_size,
    242                              copy_data) != WEBP_MUX_OK) {
    243       goto Err;
    244     }
    245     data_size = ChunkDiskSize(&chunk);
    246     id = ChunkGetIdFromTag(chunk.tag_);
    247     switch (id) {
    248       case WEBP_CHUNK_ALPHA:
    249         if (wpi->alpha_ != NULL) goto Err;  // Consecutive ALPH chunks.
    250         if (ChunkSetHead(&chunk, &wpi->alpha_) != WEBP_MUX_OK) goto Err;
    251         wpi->is_partial_ = 1;  // Waiting for a VP8 chunk.
    252         break;
    253       case WEBP_CHUNK_IMAGE:
    254         if (ChunkSetHead(&chunk, &wpi->img_) != WEBP_MUX_OK) goto Err;
    255         if (!MuxImageFinalize(wpi)) goto Err;
    256         wpi->is_partial_ = 0;  // wpi is completely filled.
    257  PushImage:
    258         // Add this to mux->images_ list.
    259         if (MuxImagePush(wpi, &mux->images_) != WEBP_MUX_OK) goto Err;
    260         MuxImageInit(wpi);  // Reset for reading next image.
    261         break;
    262       case WEBP_CHUNK_ANMF:
    263         if (wpi->is_partial_) goto Err;  // Previous wpi is still incomplete.
    264         if (!MuxImageParse(&chunk, copy_data, wpi)) goto Err;
    265         ChunkRelease(&chunk);
    266         goto PushImage;
    267         break;
    268       default:  // A non-image chunk.
    269         if (wpi->is_partial_) goto Err;  // Encountered a non-image chunk before
    270                                          // getting all chunks of an image.
    271         if (chunk_list_ends[id] == NULL) {
    272           chunk_list_ends[id] =
    273               MuxGetChunkListFromId(mux, id);  // List to add this chunk.
    274         }
    275         if (ChunkAppend(&chunk, &chunk_list_ends[id]) != WEBP_MUX_OK) goto Err;
    276         if (id == WEBP_CHUNK_VP8X) {  // grab global specs
    277           if (data_size < CHUNK_HEADER_SIZE + VP8X_CHUNK_SIZE) goto Err;
    278           mux->canvas_width_ = GetLE24(data + 12) + 1;
    279           mux->canvas_height_ = GetLE24(data + 15) + 1;
    280         }
    281         break;
    282     }
    283     data += data_size;
    284     size -= data_size;
    285     ChunkInit(&chunk);
    286   }
    287 
    288   // Incomplete image.
    289   if (wpi->is_partial_) goto Err;
    290 
    291   // Validate mux if complete.
    292   if (MuxValidate(mux) != WEBP_MUX_OK) goto Err;
    293 
    294   MuxImageDelete(wpi);
    295   return mux;  // All OK;
    296 
    297  Err:  // Something bad happened.
    298   ChunkRelease(&chunk);
    299   MuxImageDelete(wpi);
    300   WebPMuxDelete(mux);
    301   return NULL;
    302 }
    303 
    304 //------------------------------------------------------------------------------
    305 // Get API(s).
    306 
    307 // Validates that the given mux has a single image.
    308 static WebPMuxError ValidateForSingleImage(const WebPMux* const mux) {
    309   const int num_images = MuxImageCount(mux->images_, WEBP_CHUNK_IMAGE);
    310   const int num_frames = MuxImageCount(mux->images_, WEBP_CHUNK_ANMF);
    311 
    312   if (num_images == 0) {
    313     // No images in mux.
    314     return WEBP_MUX_NOT_FOUND;
    315   } else if (num_images == 1 && num_frames == 0) {
    316     // Valid case (single image).
    317     return WEBP_MUX_OK;
    318   } else {
    319     // Frame case OR an invalid mux.
    320     return WEBP_MUX_INVALID_ARGUMENT;
    321   }
    322 }
    323 
    324 // Get the canvas width, height and flags after validating that VP8X/VP8/VP8L
    325 // chunk and canvas size are valid.
    326 static WebPMuxError MuxGetCanvasInfo(const WebPMux* const mux,
    327                                      int* width, int* height, uint32_t* flags) {
    328   int w, h;
    329   uint32_t f = 0;
    330   WebPData data;
    331   assert(mux != NULL);
    332 
    333   // Check if VP8X chunk is present.
    334   if (MuxGet(mux, IDX_VP8X, 1, &data) == WEBP_MUX_OK) {
    335     if (data.size < VP8X_CHUNK_SIZE) return WEBP_MUX_BAD_DATA;
    336     f = GetLE32(data.bytes + 0);
    337     w = GetLE24(data.bytes + 4) + 1;
    338     h = GetLE24(data.bytes + 7) + 1;
    339   } else {
    340     const WebPMuxImage* const wpi = mux->images_;
    341     // Grab user-forced canvas size as default.
    342     w = mux->canvas_width_;
    343     h = mux->canvas_height_;
    344     if (w == 0 && h == 0 && ValidateForSingleImage(mux) == WEBP_MUX_OK) {
    345       // single image and not forced canvas size => use dimension of first frame
    346       assert(wpi != NULL);
    347       w = wpi->width_;
    348       h = wpi->height_;
    349     }
    350     if (wpi != NULL) {
    351       if (wpi->has_alpha_) f |= ALPHA_FLAG;
    352     }
    353   }
    354   if (w * (uint64_t)h >= MAX_IMAGE_AREA) return WEBP_MUX_BAD_DATA;
    355 
    356   if (width != NULL) *width = w;
    357   if (height != NULL) *height = h;
    358   if (flags != NULL) *flags = f;
    359   return WEBP_MUX_OK;
    360 }
    361 
    362 WebPMuxError WebPMuxGetCanvasSize(const WebPMux* mux, int* width, int* height) {
    363   if (mux == NULL || width == NULL || height == NULL) {
    364     return WEBP_MUX_INVALID_ARGUMENT;
    365   }
    366   return MuxGetCanvasInfo(mux, width, height, NULL);
    367 }
    368 
    369 WebPMuxError WebPMuxGetFeatures(const WebPMux* mux, uint32_t* flags) {
    370   if (mux == NULL || flags == NULL) return WEBP_MUX_INVALID_ARGUMENT;
    371   return MuxGetCanvasInfo(mux, NULL, NULL, flags);
    372 }
    373 
    374 static uint8_t* EmitVP8XChunk(uint8_t* const dst, int width,
    375                               int height, uint32_t flags) {
    376   const size_t vp8x_size = CHUNK_HEADER_SIZE + VP8X_CHUNK_SIZE;
    377   assert(width >= 1 && height >= 1);
    378   assert(width <= MAX_CANVAS_SIZE && height <= MAX_CANVAS_SIZE);
    379   assert(width * (uint64_t)height < MAX_IMAGE_AREA);
    380   PutLE32(dst, MKFOURCC('V', 'P', '8', 'X'));
    381   PutLE32(dst + TAG_SIZE, VP8X_CHUNK_SIZE);
    382   PutLE32(dst + CHUNK_HEADER_SIZE, flags);
    383   PutLE24(dst + CHUNK_HEADER_SIZE + 4, width - 1);
    384   PutLE24(dst + CHUNK_HEADER_SIZE + 7, height - 1);
    385   return dst + vp8x_size;
    386 }
    387 
    388 // Assemble a single image WebP bitstream from 'wpi'.
    389 static WebPMuxError SynthesizeBitstream(const WebPMuxImage* const wpi,
    390                                         WebPData* const bitstream) {
    391   uint8_t* dst;
    392 
    393   // Allocate data.
    394   const int need_vp8x = (wpi->alpha_ != NULL);
    395   const size_t vp8x_size = need_vp8x ? CHUNK_HEADER_SIZE + VP8X_CHUNK_SIZE : 0;
    396   const size_t alpha_size = need_vp8x ? ChunkDiskSize(wpi->alpha_) : 0;
    397   // Note: No need to output ANMF chunk for a single image.
    398   const size_t size = RIFF_HEADER_SIZE + vp8x_size + alpha_size +
    399                       ChunkDiskSize(wpi->img_);
    400   uint8_t* const data = (uint8_t*)WebPSafeMalloc(1ULL, size);
    401   if (data == NULL) return WEBP_MUX_MEMORY_ERROR;
    402 
    403   // There should be at most one alpha_ chunk and exactly one img_ chunk.
    404   assert(wpi->alpha_ == NULL || wpi->alpha_->next_ == NULL);
    405   assert(wpi->img_ != NULL && wpi->img_->next_ == NULL);
    406 
    407   // Main RIFF header.
    408   dst = MuxEmitRiffHeader(data, size);
    409 
    410   if (need_vp8x) {
    411     dst = EmitVP8XChunk(dst, wpi->width_, wpi->height_, ALPHA_FLAG);  // VP8X.
    412     dst = ChunkListEmit(wpi->alpha_, dst);       // ALPH.
    413   }
    414 
    415   // Bitstream.
    416   dst = ChunkListEmit(wpi->img_, dst);
    417   assert(dst == data + size);
    418 
    419   // Output.
    420   bitstream->bytes = data;
    421   bitstream->size = size;
    422   return WEBP_MUX_OK;
    423 }
    424 
    425 WebPMuxError WebPMuxGetChunk(const WebPMux* mux, const char fourcc[4],
    426                              WebPData* chunk_data) {
    427   CHUNK_INDEX idx;
    428   if (mux == NULL || fourcc == NULL || chunk_data == NULL) {
    429     return WEBP_MUX_INVALID_ARGUMENT;
    430   }
    431   idx = ChunkGetIndexFromFourCC(fourcc);
    432   if (IsWPI(kChunks[idx].id)) {     // An image chunk.
    433     return WEBP_MUX_INVALID_ARGUMENT;
    434   } else if (idx != IDX_UNKNOWN) {  // A known chunk type.
    435     return MuxGet(mux, idx, 1, chunk_data);
    436   } else {                          // An unknown chunk type.
    437     const WebPChunk* const chunk =
    438         ChunkSearchList(mux->unknown_, 1, ChunkGetTagFromFourCC(fourcc));
    439     if (chunk == NULL) return WEBP_MUX_NOT_FOUND;
    440     *chunk_data = chunk->data_;
    441     return WEBP_MUX_OK;
    442   }
    443 }
    444 
    445 static WebPMuxError MuxGetImageInternal(const WebPMuxImage* const wpi,
    446                                         WebPMuxFrameInfo* const info) {
    447   // Set some defaults for unrelated fields.
    448   info->x_offset = 0;
    449   info->y_offset = 0;
    450   info->duration = 1;
    451   info->dispose_method = WEBP_MUX_DISPOSE_NONE;
    452   info->blend_method = WEBP_MUX_BLEND;
    453   // Extract data for related fields.
    454   info->id = ChunkGetIdFromTag(wpi->img_->tag_);
    455   return SynthesizeBitstream(wpi, &info->bitstream);
    456 }
    457 
    458 static WebPMuxError MuxGetFrameInternal(const WebPMuxImage* const wpi,
    459                                         WebPMuxFrameInfo* const frame) {
    460   const int is_frame = (wpi->header_->tag_ == kChunks[IDX_ANMF].tag);
    461   const WebPData* frame_data;
    462   if (!is_frame) return WEBP_MUX_INVALID_ARGUMENT;
    463   assert(wpi->header_ != NULL);  // Already checked by WebPMuxGetFrame().
    464   // Get frame chunk.
    465   frame_data = &wpi->header_->data_;
    466   if (frame_data->size < kChunks[IDX_ANMF].size) return WEBP_MUX_BAD_DATA;
    467   // Extract info.
    468   frame->x_offset = 2 * GetLE24(frame_data->bytes + 0);
    469   frame->y_offset = 2 * GetLE24(frame_data->bytes + 3);
    470   {
    471     const uint8_t bits = frame_data->bytes[15];
    472     frame->duration = GetLE24(frame_data->bytes + 12);
    473     frame->dispose_method =
    474         (bits & 1) ? WEBP_MUX_DISPOSE_BACKGROUND : WEBP_MUX_DISPOSE_NONE;
    475     frame->blend_method = (bits & 2) ? WEBP_MUX_NO_BLEND : WEBP_MUX_BLEND;
    476   }
    477   frame->id = ChunkGetIdFromTag(wpi->header_->tag_);
    478   return SynthesizeBitstream(wpi, &frame->bitstream);
    479 }
    480 
    481 WebPMuxError WebPMuxGetFrame(
    482     const WebPMux* mux, uint32_t nth, WebPMuxFrameInfo* frame) {
    483   WebPMuxError err;
    484   WebPMuxImage* wpi;
    485 
    486   // Sanity checks.
    487   if (mux == NULL || frame == NULL) {
    488     return WEBP_MUX_INVALID_ARGUMENT;
    489   }
    490 
    491   // Get the nth WebPMuxImage.
    492   err = MuxImageGetNth((const WebPMuxImage**)&mux->images_, nth, &wpi);
    493   if (err != WEBP_MUX_OK) return err;
    494 
    495   // Get frame info.
    496   if (wpi->header_ == NULL) {
    497     return MuxGetImageInternal(wpi, frame);
    498   } else {
    499     return MuxGetFrameInternal(wpi, frame);
    500   }
    501 }
    502 
    503 WebPMuxError WebPMuxGetAnimationParams(const WebPMux* mux,
    504                                        WebPMuxAnimParams* params) {
    505   WebPData anim;
    506   WebPMuxError err;
    507 
    508   if (mux == NULL || params == NULL) return WEBP_MUX_INVALID_ARGUMENT;
    509 
    510   err = MuxGet(mux, IDX_ANIM, 1, &anim);
    511   if (err != WEBP_MUX_OK) return err;
    512   if (anim.size < kChunks[WEBP_CHUNK_ANIM].size) return WEBP_MUX_BAD_DATA;
    513   params->bgcolor = GetLE32(anim.bytes);
    514   params->loop_count = GetLE16(anim.bytes + 4);
    515 
    516   return WEBP_MUX_OK;
    517 }
    518 
    519 // Get chunk index from chunk id. Returns IDX_NIL if not found.
    520 static CHUNK_INDEX ChunkGetIndexFromId(WebPChunkId id) {
    521   int i;
    522   for (i = 0; kChunks[i].id != WEBP_CHUNK_NIL; ++i) {
    523     if (id == kChunks[i].id) return (CHUNK_INDEX)i;
    524   }
    525   return IDX_NIL;
    526 }
    527 
    528 // Count number of chunks matching 'tag' in the 'chunk_list'.
    529 // If tag == NIL_TAG, any tag will be matched.
    530 static int CountChunks(const WebPChunk* const chunk_list, uint32_t tag) {
    531   int count = 0;
    532   const WebPChunk* current;
    533   for (current = chunk_list; current != NULL; current = current->next_) {
    534     if (tag == NIL_TAG || current->tag_ == tag) {
    535       count++;  // Count chunks whose tags match.
    536     }
    537   }
    538   return count;
    539 }
    540 
    541 WebPMuxError WebPMuxNumChunks(const WebPMux* mux,
    542                               WebPChunkId id, int* num_elements) {
    543   if (mux == NULL || num_elements == NULL) {
    544     return WEBP_MUX_INVALID_ARGUMENT;
    545   }
    546 
    547   if (IsWPI(id)) {
    548     *num_elements = MuxImageCount(mux->images_, id);
    549   } else {
    550     WebPChunk* const* chunk_list = MuxGetChunkListFromId(mux, id);
    551     const CHUNK_INDEX idx = ChunkGetIndexFromId(id);
    552     *num_elements = CountChunks(*chunk_list, kChunks[idx].tag);
    553   }
    554 
    555   return WEBP_MUX_OK;
    556 }
    557 
    558 //------------------------------------------------------------------------------
    559