[cd]webp: document lack of animated webp support

Bug: webp:479
Change-Id: Iee2d7401400a5ff0a11682028194e561b365ab78

README

@@ -225,6 +225,7 @@ Usage:
 
 If input size (-s) for an image is not specified, it is
 assumed to be a PNG, JPEG, TIFF or WebP file.
+Note: Animated PNG and WebP files are not supported.
 
 Options:
   -h / -help ............. short help
@@ -344,7 +345,9 @@ The full list of options is available using -h:
 > dwebp -h
 Usage: dwebp in_file [options] [-o out_file]
 
-Decodes the WebP image file to PNG format [Default]
+Decodes the WebP image file to PNG format [Default].
+Note: Animated WebP files are not supported.
+
 Use following options to convert into alternate image formats:
   -pam ......... save the raw RGBA samples as a color PAM
   -ppm ......... save the raw RGB samples as a color PPM

examples/cwebp.c

@@ -527,6 +527,7 @@ static void HelpLong(void) {
   printf(" cwebp [-preset <...>] [options] in_file [-o out_file]\n\n");
   printf("If input size (-s) for an image is not specified, it is\n"
          "assumed to be a PNG, JPEG, TIFF or WebP file.\n");
+  printf("Note: Animated PNG and WebP files are not supported.\n");
 #ifdef HAVE_WINCODEC_H
   printf("Windows builds can take as input any of the files handled by WIC.\n");
 #endif

examples/dwebp.c

@@ -76,7 +76,8 @@ static int SaveOutput(const WebPDecBuffer* const buffer,
 
 static void Help(void) {
   printf("Usage: dwebp in_file [options] [-o out_file]\n\n"
-         "Decodes the WebP image file to PNG format [Default]\n"
+         "Decodes the WebP image file to PNG format [Default].\n"
+         "Note: Animated WebP files are not supported.\n\n"
          "Use following options to convert into alternate image formats:\n"
          "  -pam ......... save the raw RGBA samples as a color PAM\n"
          "  -ppm ......... save the raw RGB samples as a color PPM\n"

man/cwebp.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH CWEBP 1 "January 11, 2019"
+.TH CWEBP 1 "November 19, 2020"
 .SH NAME
 cwebp \- compress an image file to a WebP file
 .SH SYNOPSIS
@@ -13,6 +13,7 @@ command.
 .PP
 \fBcwebp\fP compresses an image using the WebP format.
 Input format can be either PNG, JPEG, TIFF, WebP or raw Y'CbCr samples.
+Note: Animated PNG and WebP files are not supported.
 .SH OPTIONS
 The basic options are:
 .TP

man/dwebp.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH DWEBP 1 "June 23, 2016"
+.TH DWEBP 1 "November 19, 2020"
 .SH NAME
 dwebp \- decompress a WebP file to an image file
 .SH SYNOPSIS
@@ -12,6 +12,7 @@ This manual page documents the
 command.
 .PP
 \fBdwebp\fP decompresses WebP files into PNG, PAM, PPM or PGM images.
+Note: Animated WebP files are not supported.
 .SH OPTIONS
 The basic options are:
 .TP