libwebp/README.mux

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Description:
============

WebP Mux: library to create a WebP container object for features like
color profile, metadata, animation and fragmented images. A reference command
line tool 'webpmux' and WebP container specification
'doc/webp-container-spec.txt' are also provided in this package.

WebP Mux tool:
==============

The examples/ directory contains a tool (webpmux) for manipulating WebP
files. The webpmux tool can be used to create a WebP container file and to
extract or strip relevant data from the container file.

A list of options is available using the -help command line flag:

> webpmux -help
Usage: webpmux -get GET_OPTIONS INPUT -o OUTPUT
       webpmux -set SET_OPTIONS INPUT -o OUTPUT
       webpmux -strip STRIP_OPTIONS INPUT -o OUTPUT
       webpmux -frgm FRAGMENT_OPTIONS [-frgm...] -o OUTPUT
       webpmux -frame FRAME_OPTIONS [-frame...] [-loop LOOP_COUNT]
               [-bgcolor BACKGROUND_COLOR] -o OUTPUT
       webpmux -info INPUT
       webpmux [-h|-help]

GET_OPTIONS:
 Extract relevant data.
   icc       Get ICC profile.
   exif      Get EXIF metadata.
   xmp       Get XMP metadata.
   frgm n    Get nth fragment.
   frame n   Get nth frame.

SET_OPTIONS:
 Set color profile/metadata.
   icc  file.icc     Set ICC profile.
   exif file.exif    Set EXIF metadata.
   xmp  file.xmp     Set XMP metadata.
   where:    'file.icc' contains the ICC profile to be set,
             'file.exif' contains the EXIF metadata to be set and
             'file.xmp' contains the XMP metadata to be set

STRIP_OPTIONS:
 Strip color profile/metadata.
   icc       Strip ICC profile.
   exif      Strip EXIF metadata.
   xmp       Strip XMP metadata.

FRAGMENT_OPTIONS(i):
 Create fragmented image.
   file_i +xi+yi
   where:    'file_i' is the i'th fragment (WebP format),
             'xi','yi' specify the image offset for this fragment.

FRAME_OPTIONS(i):
 Create animation.
   file_i +xi+yi+di+mi
   where:    'file_i' is the i'th animation frame (WebP format),
             'xi','yi' specify the image offset for this frame.
             'di' is the pause duration before next frame.
             'mi' is the dispose method for this frame (0 or 1).

LOOP_COUNT:
 Number of times to repeat the animation.
 Valid range is 0 to 65535 [Default: 0 (infinite)].

BACKGROUND_COLOR:
 Background color of the canvas.
  A,R,G,B
  where:    'A', 'R', 'G' and 'B' are integers in the range 0 to 255 specifying
            the Alpha, Red, Green and Blue component values respectively
            [Default: 255,255,255,255].

INPUT & OUTPUT are in WebP format.

Note: The nature of EXIF, XMP and ICC data is not checked and is assumed to be
valid.

WebP Mux API:
==============
The WebP Mux API contains methods for adding data to and reading data from
WebPMux (a WebP container object). This API currently supports XMP/EXIF
metadata, ICC profile, animation and fragmented images. Other features
will be added in subsequent releases.

Example#1 (pseudo code): Creating a WebPMux object with image data, color
profile and XMP metadata.

  int copy_data = 0;
  WebPMux* mux = WebPMuxNew();
  // ... (Prepare image data).
  WebPMuxSetImage(mux, &image, copy_data);
  // ... (Prepare ICC profile data).
  WebPMuxSetChunk(mux, "ICCP", &icc_profile, copy_data);
  // ... (Prepare XMP metadata).
  WebPMuxSetChunk(mux, "XMP ", &xmp, copy_data);
  // Get data from mux in WebP RIFF format.
  WebPMuxAssemble(mux, &output_data);
  WebPMuxDelete(mux);
  // ... (Consume output_data; e.g. write output_data.bytes to file).
  WebPDataClear(&output_data);


Example#2 (pseudo code): Get image and color profile data from a WebP file.

  int copy_data = 0;
  // ... (Read data from file).
  WebPMux* mux = WebPMuxCreate(&data, copy_data);
  WebPMuxGetFrame(mux, 1, &image);
  // ... (Consume image; e.g. call WebPDecode() to decode the data).
  WebPMuxGetChunk(mux, "ICCP", &icc_profile);
  // ... (Consume icc_profile).
  WebPMuxDelete(mux);
  free(data);


For detailed Mux API reference, please refer to the header file (src/webp/mux.h)

Bugs:
=====

Please report all bugs to our issue tracker:
    http://code.google.com/p/webp/issues
Patches welcome! See this page to get started:
    http://www.webmproject.org/code/contribute/submitting-patches/

Discuss:
========

Email: webp-discuss@webmproject.org
Web: http://groups.google.com/a/webmproject.org/group/webp-discuss