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MUX API Updates

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- Add alpha support in mux.
- Remove WebPMuxAddNamedData() and WebPMuxGetNamedData() APIs. Add WebPMuxSetImage(), WebPmuxGetImage() and WebPMuxDeleteImage() APIs instead.
- Refactor code using WebPImage struct.
- Corresponding changes in webpmux binary.
- WebPMuxSetImage()/AddFrame()/AddTile() can now work with data which starts from "RIFF...". This simplifies reading a single-image webp file and adding it as an image/frame/tile in mux.

Change-Id: I7d98a6407dfe55c84a682ef7e46bc622f5a6f8d9
This commit is contained in:
Urvang Joshi 2011-11-22 14:40:41 +05:30
parent 059f03ef99
commit c398f59536
5 changed files with 779 additions and 374 deletions
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6
README.mux
View File

@ -73,7 +73,8 @@ metadata.
int copy_data = 0;
WebPMux* mux = WebPMuxNew();
// ... (Prepare image data).
WebPMuxAddNamedData(mux, 1, "image", image_data, image_data_size, copy_data);
WebPMuxSetImage(mux, image_data, image_data_size, alpha_data, alpha_size,
copy_data);
// ... (Prepare ICCP color profile data).
WebPMuxSetColorProfile(mux, icc_data, icc_data_size, copy_data);
// ... (Prepare XMP metadata).
@ -90,7 +91,8 @@ Example#2 (pseudo code): Get image & color profile data from a WebP file.
int copy_data = 0;
// ... (Read data from file).
WebPMux* mux = WebPMuxCreate(data, data_size, copy_data);
WebPMuxGetNamedData(mux, "image", 1, &image_data, &image_data_size);
WebPMuxGetImage(mux, &image_data, &image_data_size,
&alpha_data, &alpha_size);
// ... (Consume image_data; e.g. call WebPDecode() to decode the data).
WebPMuxGetColorProfile(mux, &icc_data, &icc_data_size);
// ... (Consume icc_data).

75
doc/webp-container-spec.txt
View File

@ -50,6 +50,9 @@ document describes additional support for:
* **Animation.** An image may have pauses between frames, making it
an animation.
* **Transparency.** An image may have transparency, i.e., an alpha channel for
each frame/tile.
Files not using these new features are backward compatible with the
original format. Use of these features will produce files that are not
compatible with older programs.
@ -215,6 +218,10 @@ multiple frames. Data for each frame consists of:
present at the beginning of data for an image that's represented as
multiple tile images.
* An optional "ALPH" chunk with alpha bitstream of the tile. It **MUST** be
present for an image containing transparency. It **MUST NOT** be present
in non-transparent images.
* A "VP8 " chunk with the bitstream of the tile.
All chunks **MUST** be placed in the same order as listed above (except
@ -228,8 +235,8 @@ position, a decoder can choose to stop searching for it. The rule of
ignoring late chunks should make programs that need to do a full search
give the same results as the ones stopping early.
**Example:** An example layout of a non-animated, tiled image may look
as follows:
**Example:** An example layout of a non-animated, tiled image without
transparency may look as follows:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RIFF/WEBP
@ -246,17 +253,20 @@ RIFF/WEBP
+- META (XMP metadata)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
**Example:** An example layout of an animated image may look as follows:
**Example:** An example layout of an animated image with transparency may look
as follows:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RIFF/WEBP
+- VP8X (descriptions of features used)
+- LOOP (animation control parameters)
+- FRM (first animation frame parameters)
+- ALPH (alpha bitstream - first image frame)
+- VP8 (bitstream - first image frame)
+- FRM (second animation frame parameters)
+- ALPH (alpha bitstream - second image frame)
+- VP8 (bitstream - second image frame)
+- META(XMP metadata)
+- META (XMP metadata)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -272,14 +282,20 @@ pseudocode:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
assert not VP8X.flags.haveAnimation
canvas ← new black image of size VP8X.canvasWidth x VP8X.canvasHeight.
canvas ← new black image of size
VP8X.canvasWidth x VP8X.canvasHeight.
tile_params.tileCanvasX = tile_params.tileCanvasY = 0
for chunk in data_for_all_frames:
if chunk.tag == "TILE":
assert No other TILE chunk after the last "VP8 " chunk
assert No ALPH chunk after the last "VP8 " chunk
tile_params = chunk
if chunk.tag == "ALPH":
assert No other ALPH chunk after the last "VP8 " chunk
tile_params.alpha = alpha_data
if chunk.tag == "VP8 ":
render image in chunk in canvas with top-left corner in (tile_params.tileCanvasX, tile_params.tileCanvasY) using the isometry in VP8X.flags.rotationAndSymmetry.
render image in chunk in canvas with top-left corner in
(tile_params.tileCanvasX, tile_params.tileCanvasY).
tile_params.tileCanvasX = tile_params.tileCanvasY = 0
Ignore unknown chunks
canvas contains the decoded canvas.
@ -290,7 +306,8 @@ pseudocode:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
assert VP8X.flags.haveAnimation
canvas ← new black image of size VP8X.canvasWidth x VP8X.canvasHeight.
canvas ← new black image of size
VP8X.canvasWidth x VP8X.canvasHeight.
if LOOP.loopCount==0:
LOOP.loopCount=∞
current_FRM ← nil
@ -298,15 +315,24 @@ for LOOP.loop = 0, ..., LOOP.loopCount-1
assert First chunk in data_for_all_frames is a FRM
for chunk in data_for_all_frames:
if chunk.tag == "FRM ":
assert No other FRM chunk after the last "VP8 " chunk
assert No ALPH chunk after the last "VP8 " chunk
if current_FRM != nil:
Show the contents of canvas for current_FRM.frameDuration*10ms.
Show the contents of canvas for
current_FRM.frameDuration * 1ms.
current_FRM = chunk
if chunk.tag == "ALPH":
assert No other ALPH chunk after the last "VP8 " chunk
tile_params.alpha = alpha_data
if chunk.tag == "VP8 ":
assert tile_params.tileCanvasX >= current_FRM.frameX
assert tile_params.tileCanvasY >= current_FRM.frameY
assert tile_params.tileCanvasX + chunk.tileWidth >= current_FRM.frameX + current_FRM.frameWidth
assert tile_params.tileCanvasY + chunk.tileHeight >= current_FRM.frameX + current_FRM.frameHeight
render image in chunk in canvas with top-left corner in (tile_params.tileCanvasX, tile_params.tileCanvasY) using the isometry in VP8X.flags.rotationAndSymmetry.
assert tile_params.tileCanvasX + chunk.tileWidth >=
current_FRM.frameX + current_FRM.frameWidth
assert tile_params.tileCanvasY + chunk.tileHeight >=
current_FRM.frameX + current_FRM.frameHeight
render image in chunk in canvas with top-left corner in
(tile_params.tileCanvasX, tile_params.tileCanvasY).
tile_params.tileCanvasX = tile_params.tileCanvasY = 0
Ignore unknown chunks
canvas contains the decoded canvas.
@ -482,6 +508,31 @@ constraints:
_tileCanvasY + tileHeight == canvasHeight_ **MUST** be true.
### ALPH Chunks (Alpha Bitstreams)
This optional chunk contains encoded alpha data for a single tile. Either
**ALL or NONE** of the tiles must contain this chunk.
The alpha channel can be encoded either losslessly or with lossy preprocessing
(quantization). After the optional preprocessing, the alpha values are encoded
with a lossless compression method like zlib. Work is in progress to improve the
compression gain further by exploring alternate compression methods and hence,
the bit-stream for the Alpha-chunk is still experimental and expected to change.
The contents of such a chunk are as follows:
* Byte 0: The _compression method_ used. Currently two methods are
supported:
* 0 --> No compression
* 1 --> Zlib compression.
* Byte 1: _Reserved_. **Should** be 0.
* Byte 2 onwards: _Encoded alpha bitstream_.
### ICCP Chunk (Color Profile)
An optional "ICCP" chunk contains an ICC profile. There **SHOULD** be
@ -525,4 +576,4 @@ specification. Such chunks **MUST** be ignored, but preserved. Writers
[vp8spec]: http://tools.ietf.org/html/draft-bankoski-vp8-bitstream
[xmpspec]: http://www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMPSpecificationPart1.pdf
[metadata]: http://www.metadataworkinggroup.org/pdf/mwg_guidance.pdf
[metadata]: http://www.metadataworkinggroup.org/pdf/mwg_guidance.pdf

70
examples/webpmux.c
View File

@ -191,8 +191,8 @@ static WebPMuxError DisplayInfo(const WebPMux* mux) {
fprintf(stderr, "No.: x_offset y_offset duration\n");
for (i = 1; i <= nFrames; i++) {
err = WebPMuxGetFrame(mux, i, &data, &size, &x_offset, &y_offset,
&duration);
err = WebPMuxGetFrame(mux, i, &data, &size, NULL, NULL,
&x_offset, &y_offset, &duration);
assert(err == WEBP_MUX_OK);
fprintf(stderr, "%3d: %8d %8d %8d\n", i, x_offset, y_offset, duration);
}
@ -209,7 +209,8 @@ static WebPMuxError DisplayInfo(const WebPMux* mux) {
uint32_t x_offset, y_offset;
fprintf(stderr, "No.: x_offset y_offset\n");
for (i = 1; i <= nTiles; i++) {
err = WebPMuxGetTile(mux, i, &data, &size, &x_offset, &y_offset);
err = WebPMuxGetTile(mux, i, &data, &size, NULL, NULL,
&x_offset, &y_offset);
assert(err == WEBP_MUX_OK);
fprintf(stderr, "%3d: %8d %8d\n", i, x_offset, y_offset);
}
@ -350,45 +351,6 @@ static int ReadFile(const char* const filename, WebPMux** mux) {
return 0;
}
static int ReadImageData(const char* filename, int image_index,
const uint8_t** data_ptr, uint32_t* size_ptr) {
uint32_t size = 0;
void* data = NULL;
WebPMux* mux;
WebPMuxError err;
int ok = 1;
if (!ReadData(filename, &data, &size)) return 0;
mux = WebPMuxCreate((const uint8_t*)data, size, 1);
free(data);
if (mux == NULL) {
fprintf(stderr, "Failed to create mux object from file %s.\n",
filename);
return 0;
}
err = WebPMuxGetNamedData(mux, "image", image_index, (const uint8_t**)&data,
&size);
if (err == WEBP_MUX_OK) {
*size_ptr = size;
*data_ptr = (uint8_t*)malloc(*size_ptr);
if (*data_ptr != NULL) {
memcpy((void*)*data_ptr, data, (size_t)size);
} else {
err = WEBP_MUX_MEMORY_ERROR;
fprintf(stderr, "Failed to allocate %d bytes to extract image data from"
" file %s. Error: %d\n", size, filename, err);
ok = 0;
}
} else {
fprintf(stderr, "Failed to extract image data from file %s. Error: %d\n",
filename, err);
ok = 0;
}
WebPMuxDelete(mux);
return ok;
}
static int WriteData(const char* filename, void* data, uint32_t size) {
int ok = 0;
FILE* fout = strcmp(filename, "-") ? fopen(filename, "wb") : stdout;
@ -770,13 +732,14 @@ static int GetFrameTile(const WebPMux* mux,
}
if (isFrame) {
err = WebPMuxGetFrame(mux, num, &data, &size, &x_offset, &y_offset,
&duration);
err = WebPMuxGetFrame(mux, num, &data, &size, NULL, NULL,
&x_offset, &y_offset, &duration);
if (err != WEBP_MUX_OK) {
ERROR_GOTO3("ERROR#%d: Could not get frame %ld.\n", err, num, ErrGet);
}
} else {
err = WebPMuxGetTile(mux, num, &data, &size, &x_offset, &y_offset);
err = WebPMuxGetTile(mux, num, &data, &size, NULL, NULL,
&x_offset, &y_offset);
if (err != WEBP_MUX_OK) {
ERROR_GOTO3("ERROR#%d: Could not get frame %ld.\n", err, num, ErrGet);
}
@ -787,7 +750,7 @@ static int GetFrameTile(const WebPMux* mux,
err = WEBP_MUX_MEMORY_ERROR;
ERROR_GOTO2("ERROR#%d: Could not allocate a mux object.\n", err, ErrGet);
}
err = WebPMuxAddNamedData(mux_single, 0, "image", data, size, 1);
err = WebPMuxSetImage(mux_single, data, size, NULL, 0, 1);
if (err != WEBP_MUX_OK) {
ERROR_GOTO2("ERROR#%d: Could not create single image mux object.\n", err,
ErrGet);
@ -870,8 +833,8 @@ static int Process(const WebPMuxConfig* config) {
ERROR_GOTO2("ERROR#%d: Could not set loop count.\n", err, Err2);
}
} else if (feature->args_[index].subtype_ == SUBTYPE_FRM) {
ok = ReadImageData(feature->args_[index].filename_, 1,
&data, &size);
ok = ReadData(feature->args_[index].filename_,
(void**)&data, &size);
if (!ok) goto Err2;
ok = ParseFrameArgs(feature->args_[index].params_,
&x_offset, &y_offset, &duration);
@ -879,8 +842,8 @@ static int Process(const WebPMuxConfig* config) {
free((void*)data);
ERROR_GOTO1("ERROR: Could not parse frame properties.\n", Err2);
}
err = WebPMuxAddFrame(mux, 0, data, size, x_offset, y_offset,
duration, 1);
err = WebPMuxAddFrame(mux, 0, data, size, NULL, 0,
x_offset, y_offset, duration, 1);
free((void*)data);
if (err != WEBP_MUX_OK) {
ERROR_GOTO3("ERROR#%d: Could not add a frame at index %d.\n",
@ -899,8 +862,8 @@ static int Process(const WebPMuxConfig* config) {
WEBP_MUX_MEMORY_ERROR, Err2);
}
for (index = 0; index < feature->arg_count_; ++index) {
ok = ReadImageData(feature->args_[index].filename_, 1,
&data, &size);
ok = ReadData(feature->args_[index].filename_,
(void**)&data, &size);
if (!ok) goto Err2;
ok = ParseTileArgs(feature->args_[index].params_, &x_offset,
&y_offset);
@ -908,7 +871,8 @@ static int Process(const WebPMuxConfig* config) {
free((void*)data);
ERROR_GOTO1("ERROR: Could not parse tile properties.\n", Err2);
}
err = WebPMuxAddTile(mux, 0, data, size, x_offset, y_offset, 1);
err = WebPMuxAddTile(mux, 0, data, size, NULL, 0,
x_offset, y_offset, 1);
free((void*)data);
if (err != WEBP_MUX_OK) {
ERROR_GOTO3("ERROR#%d: Could not add a tile at index %d.\n",

867
src/mux/mux.c
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File diff suppressed because it is too large Load Diff

135
src/webp/mux.h
View File

@ -18,8 +18,8 @@
// int copy_data = 0;
// WebPMux* mux = WebPMuxNew();
// // ... (Prepare image data).
// WebPMuxAddNamedData(mux, 1, "image", image_data, image_data_size,
// copy_data);
// WebPMuxSetImage(mux, image_data, image_data_size, alpha_data, alpha_size,
// copy_data);
// // ... (Prepare ICCP color profile data).
// WebPMuxSetColorProfile(mux, icc_data, icc_data_size, copy_data);
// // ... (Prepare XMP metadata).
@ -35,7 +35,8 @@
// int copy_data = 0;
// // ... (Read data from file).
// WebPMux* mux = WebPMuxCreate(data, data_size, copy_data);
// WebPMuxGetNamedData(mux, "image", 1, &image_data, &image_data_size);
// WebPMuxGetImage(mux, &image_data, &image_data_size,
// &alpha_data, &alpha_size);
// // ... (Consume image_data; e.g. call WebPDecode() to decode the data).
// WebPMuxGetColorProfile(mux, &icc_data, &icc_data_size);
// // ... (Consume icc_data).
@ -67,7 +68,8 @@ typedef enum {
TILE_FLAG = 0x00000001,
ANIMATION_FLAG = 0x00000002,
ICCP_FLAG = 0x00000004,
META_FLAG = 0x00000008
META_FLAG = 0x00000008,
ALPHA_FLAG = 0x00000010
} FeatureFlags;
typedef struct WebPMux WebPMux; // main opaque object.
@ -100,6 +102,57 @@ WEBP_EXTERN(void) WebPMuxDelete(WebPMux* const mux);
WEBP_EXTERN(WebPMux*) WebPMuxCreate(const uint8_t* data, uint32_t size,
int copy_data);
//------------------------------------------------------------------------------
// Single Image.
// Sets the image in the mux object. Any existing images (including frame/tile)
// will be removed.
// Parameters:
// mux - (in/out) object in which the image is to be set
// data - (in) the image data to be set. The data can be either a VP8
// bitstream or a single-image WebP file (non-animated & non-tiled)
// size - (in) size of the image data
// alpha_data - (in) the alpha data corresponding to the image (if present)
// alpha_size - (in) size of alpha chunk data
// copy_data - (in) value 1 indicates given data WILL copied to the mux, and
// value 0 indicates data will NOT be copied.
// Returns:
// WEBP_MUX_INVALID_ARGUMENT - if mux is NULL or data is NULL.
// WEBP_MUX_MEMORY_ERROR - on memory allocation error.
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxSetImage(WebPMux* const mux,
const uint8_t* data, uint32_t size,
const uint8_t* alpha_data,
uint32_t alpha_size, int copy_data);
// Gets a reference to the image in the mux object.
// The caller should NOT free the returned data.
// Parameters:
// mux - (in) object from which the image is to be fetched
// data - (out) the returned image data
// size - (out) size of the returned image data
// alpha_data - (in) the returned alpha data of the image (if present)
// alpha_size - (in) size of alpha chunk data
// Returns:
// WEBP_MUX_INVALID_ARGUMENT - if either of mux, data or size is NULL
// OR if mux contains animation/tiling.
// WEBP_MUX_NOT_FOUND - if image is not present in mux object.
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxGetImage(const WebPMux* const mux,
const uint8_t** data, uint32_t* size,
const uint8_t** alpha_data,
uint32_t* alpha_size);
// Deletes the image in the mux object.
// Parameters:
// mux - (in/out) object from which the image is to be deleted
// Returns:
// WEBP_MUX_INVALID_ARGUMENT - if mux is NULL
// OR if mux contains animation/tiling.
// WEBP_MUX_NOT_FOUND - if image is not present in mux object.
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxDeleteImage(WebPMux* const mux);
//------------------------------------------------------------------------------
// XMP Metadata.
@ -192,8 +245,12 @@ WEBP_EXTERN(WebPMuxError) WebPMuxDeleteColorProfile(WebPMux* const mux);
// Parameters:
// mux - (in/out) object to which an animation frame is to be added
// nth - (in) The position at which the frame is to be added.
// data - (in) the raw VP8 image data corresponding to frame image
// data - (in) the raw VP8 image data corresponding to frame image. The data
// can be either a VP8 bitstream or a single-image WebP file
// (non-animated & non-tiled)
// size - (in) size of frame chunk data
// alpha_data - (in) the alpha data corresponding to frame image (if present)
// alpha_size - (in) size of alpha chunk data
// x_offset - (in) x-offset of the frame to be added
// y_offset - (in) y-offset of the frame to be added
// duration - (in) duration of the frame to be added (in milliseconds)
@ -206,9 +263,22 @@ WEBP_EXTERN(WebPMuxError) WebPMuxDeleteColorProfile(WebPMux* const mux);
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxAddFrame(WebPMux* const mux, uint32_t nth,
const uint8_t* data, uint32_t size,
const uint8_t* alpha_data,
uint32_t alpha_size,
uint32_t x_offset, uint32_t y_offset,
uint32_t duration, int copy_data);
// TODO(urvang): Create a struct as follows to reduce argument list size:
// typedef struct {
// int nth;
// uint8_t* data;
// uint32_t data_size;
// uint8_t* alpha;
// uint32_t alpha_size;
// uint32_t x_offset, y_offset;
// uint32_t duration;
// } FrameInfo;
// Gets a reference to the nth animation frame from the mux object.
// The caller should NOT free the returned data.
// nth=0 has a special meaning - last position.
@ -217,6 +287,8 @@ WEBP_EXTERN(WebPMuxError) WebPMuxAddFrame(WebPMux* const mux, uint32_t nth,
// nth - (in) index of the frame in the mux object
// data - (out) the returned image data
// size - (out) size of the returned image data
// alpha_data - (in) the alpha data corresponding to frame image (if present)
// alpha_size - (in) size of alpha chunk data
// x_offset - (out) x-offset of the returned frame
// y_offset - (out) y-offset of the returned frame
// duration - (out) duration of the returned frame (in milliseconds)
@ -229,6 +301,8 @@ WEBP_EXTERN(WebPMuxError) WebPMuxAddFrame(WebPMux* const mux, uint32_t nth,
WEBP_EXTERN(WebPMuxError) WebPMuxGetFrame(const WebPMux* const mux,
uint32_t nth,
const uint8_t** data, uint32_t* size,
const uint8_t** alpha_data,
uint32_t* alpha_size,
uint32_t* x_offset,
uint32_t* y_offset,
uint32_t* duration);
@ -277,8 +351,12 @@ WEBP_EXTERN(WebPMuxError) WebPMuxGetLoopCount(const WebPMux* const mux,
// Parameters:
// mux - (in/out) object to which a tile is to be added
// nth - (in) The position at which the tile is to be added.
// data - (in) the raw VP8 image data corresponding to tile image
// data - (in) the raw VP8 image data corresponding to tile image. The data
// can be either a VP8 bitstream or a single-image WebP file
// (non-animated & non-tiled)
// size - (in) size of tile chunk data
// alpha_data - (in) the alpha data corresponding to tile image (if present)
// alpha_size - (in) size of alpha chunk data
// x_offset - (in) x-offset of the tile to be added
// y_offset - (in) y-offset of the tile to be added
// copy_data - (in) value 1 indicates given data WILL copied to the mux, and
@ -290,6 +368,8 @@ WEBP_EXTERN(WebPMuxError) WebPMuxGetLoopCount(const WebPMux* const mux,
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxAddTile(WebPMux* const mux, uint32_t nth,
const uint8_t* data, uint32_t size,
const uint8_t* alpha_data,
uint32_t alpha_size,
uint32_t x_offset, uint32_t y_offset,
int copy_data);
@ -301,6 +381,8 @@ WEBP_EXTERN(WebPMuxError) WebPMuxAddTile(WebPMux* const mux, uint32_t nth,
// nth - (in) index of the tile in the mux object
// data - (out) the returned image data
// size - (out) size of the returned image data
// alpha_data - (in) the alpha data corresponding to tile image (if present)
// alpha_size - (in) size of alpha chunk data
// x_offset - (out) x-offset of the returned tile
// y_offset - (out) y-offset of the returned tile
// Returns:
@ -311,6 +393,8 @@ WEBP_EXTERN(WebPMuxError) WebPMuxAddTile(WebPMux* const mux, uint32_t nth,
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxGetTile(const WebPMux* const mux, uint32_t nth,
const uint8_t** data, uint32_t* size,
const uint8_t** alpha_data,
uint32_t* alpha_size,
uint32_t* x_offset,
uint32_t* y_offset);
@ -329,45 +413,6 @@ WEBP_EXTERN(WebPMuxError) WebPMuxDeleteTile(WebPMux* const mux, uint32_t nth);
//------------------------------------------------------------------------------
// Misc Utilities.
// Adds a chunk with given tag at nth position.
// nth=0 has a special meaning - last position.
// Parameters:
// mux - (in/out) object to which a chunk is to be added
// nth - (in) The position at which the chunk is to be added.
// tag - (in) tag name specifying the type of chunk
// data - (in) the chunk data
// size - (in) size of tile chunk data
// copy_data - (in) value 1 indicates given data WILL copied to the mux, and
// value 0 indicates data will NOT be copied.
// Returns:
// WEBP_MUX_INVALID_ARGUMENT - if either mux, tag or data is NULL
// WEBP_MUX_INVALID_PARAMETER - if tag is invalid.
// WEBP_MUX_MEMORY_ERROR - on memory allocation error.
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxAddNamedData(WebPMux* const mux, uint32_t nth,
const char* const tag,
const uint8_t* data,
uint32_t size, int copy_data);
// Gets a reference to the nth chunk having tag value tag in the mux object.
// The caller should NOT free the returned data.
// nth=0 has a special meaning - last position.
// Parameters:
// mux - (in) object from which a chunk is to be fetched
// tag - (in) tag name specifying which type of chunk is to be fetched
// nth - (in) chunk index corresponding to the specified tag to be fetched
// data - (out) raw data of the chunk returned
// size - (out) size of the returned data
// Returns:
// WEBP_MUX_INVALID_ARGUMENT - if either mux, tag, data or size is NULL
// WEBP_MUX_NOT_FOUND - If there are less than nth named elements in the mux
// object.
// WEBP_MUX_OK - on success.
WEBP_EXTERN(WebPMuxError) WebPMuxGetNamedData(const WebPMux* const mux,
const char* tag, uint32_t nth,
const uint8_t** data,
uint32_t* size);
// Gets the feature flags from the mux object.
// Parameters:
// mux - (in) object from which the features are to be fetched