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  -f <int> ............... filter strength (0=off..100)
  -metadata <string> ..... comma separated list of metadata to
                           copy from the input to the output if present
                           Valid values: all, none, icc, xmp (default)
  -mt .................... use multi-threading if available

  -version ............... print version number and exit
  -v ..................... verbose
  -quiet ................. don't print anything

Building:
---------
With the libgif development files installed, gif2webp can be built using
makefile.unix:
$ make -f makefile.unix examples/gif2webp

or using autoconf:
$ ./configure --enable-everything
$ make

Encoding API:
=============

The main encoding functions are available in the header src/webp/encode.h
The ready-to-use ones are:
size_t WebPEncodeRGB(const uint8_t* rgb, int width, int height, int stride,
                     float quality_factor, uint8_t** output);
size_t WebPEncodeBGR(const uint8_t* bgr, int width, int height, int stride,
                     float quality_factor, uint8_t** output);
size_t WebPEncodeRGBA(const uint8_t* rgba, int width, int height, int stride,
                      float quality_factor, uint8_t** output);
size_t WebPEncodeBGRA(const uint8_t* bgra, int width, int height, int stride,
                      float quality_factor, uint8_t** output);

They will convert raw RGB samples to a WebP data. The only control supplied
is the quality factor.

There are some variants for using the lossless format:

size_t WebPEncodeLosslessRGB(const uint8_t* rgb, int width, int height,
                             int stride, uint8_t** output);
size_t WebPEncodeLosslessBGR(const uint8_t* bgr, int width, int height,
                             int stride, uint8_t** output);
size_t WebPEncodeLosslessRGBA(const uint8_t* rgba, int width, int height,
                              int stride, uint8_t** output);
size_t WebPEncodeLosslessBGRA(const uint8_t* bgra, int width, int height,
                              int stride, uint8_t** output);

Of course in this case, no quality factor is needed since the compression
occurs without loss of the input values, at the expense of larger output sizes.

Advanced encoding API:
----------------------

A more advanced API is based on the WebPConfig and WebPPicture structures.

WebPConfig contains the encoding settings and is not tied to a particular
picture.
WebPPicture contains input data, on which some WebPConfig will be used for
compression.
The encoding flow looks like:

-------------------------------------- BEGIN PSEUDO EXAMPLE

#include <webp/encode.h>

  // Setup a config, starting form a preset and tuning some additional
  // parameters
  WebPConfig config;
  if (!WebPConfigPreset(&config, WEBP_PRESET_PHOTO, quality_factor))
    return 0;   // version error
  }
  // ... additional tuning
  config.sns_strength = 90;
  config.filter_sharpness = 6;
  config_error = WebPValidateConfig(&config);  // not mandatory, but useful

  // Setup the input data
  WebPPicture pic;
  if (!WebPPictureInit(&pic)) {
    return 0;  // version error
  }
  pic.width = width;
  pic.height = height;
  // allocated picture of dimension width x height
  if (!WebPPictureAllocate(&pic)) {
    return 0;   // memory error
  }
  // at this point, 'pic' has been initialized as a container,
  // and can receive the Y/U/V samples.
  // Alternatively, one could use ready-made import functions like
  // WebPPictureImportRGB(), which will take care of memory allocation.
  // In any case, past this point, one will have to call
  // WebPPictureFree(&pic) to reclaim memory.

  // Set up a byte-output write method. WebPMemoryWriter, for instance.
  WebPMemoryWriter wrt;
  WebPMemoryWriterInit(&wrt);     // initialize 'wrt'

  pic.writer = MyFileWriter;
  pic.custom_ptr = my_opaque_structure_to_make_MyFileWriter_work;

  // Compress!
  int ok = WebPEncode(&config, &pic);   // ok = 0 => error occurred!
  WebPPictureFree(&pic);  // must be called independently of the 'ok' result.

  // output data should have been handled by the writer at that point.
  // -> compressed data is the memory buffer described by wrt.mem / wrt.size

  // deallocate the memory used by compressed data
  WebPMemoryWriterClear(&wrt);

-------------------------------------- END PSEUDO EXAMPLE

Decoding API:
=============

This is mainly just one function to call:

#include "webp/decode.h"
uint8_t* WebPDecodeRGB(const uint8_t* data, size_t data_size,