webpmux -duration: set default 'end' value equal to 'start'

The options are now:
  -duration d     -> set the whole animation to duration 'd'
  -duration d,s   -> set only frame 's' to duration 'd'
  -duration d,s,e -> set only interval [s,d] to duration 'd'

+ style fix

Change-Id: I72e95282d520146f76696666f44280ad9506affa

README.mux

@@ -51,12 +51,15 @@ SET_OPTIONS:
              'file.xmp' contains the XMP metadata to be set
 
 DURATION_OPTIONS:
- Set constant duration of frames:
+ Set duration of selected frames:
-   duration[,start[,end]]
+   duration            set duration for each frames
-   where: 'duration' is the duration in milliseconds,
+   duration,frame      set duration of a particular frame
-          'start' is the start frame index (optional)(default=1),
+   duration,start,end  set duration of frames in the
-          'end' is the inclusive end frame index (optional).
+                        interval [start,end])
-           The special value '0' means: last frame (default=0).
+   where: 'duration' is the duration in milliseconds
+          'start' is the start frame index
+          'end' is the inclusive end frame index
+           The special 'end' value '0' means: last frame.
 
 STRIP_OPTIONS:
  Strip color profile/metadata:

examples/webpmux.c

@@ -40,8 +40,8 @@
 
   Change duration of frame intervals:
     webpmux -duration 150 in.webp -o out.webp
-    webpmux -duration 33,10,0 in.webp -o out.webp
+    webpmux -duration 33,2 in.webp -o out.webp
-    webpmux -duration 200,2 -duration 150,0,50 in.webp -o out.webp
+    webpmux -duration 200,10,0 -duration 150,6,50 in.webp -o out.webp
 
   Misc:
     webpmux -info in.webp
@@ -322,12 +322,15 @@ static void PrintHelp(void) {
 
   printf("\n");
   printf("DURATION_OPTIONS:\n");
-  printf(" Set constant duration of frames:\n");
+  printf(" Set duration of selected frames:\n");
-  printf("   duration[,start[,end]]\n");
+  printf("   duration            set duration for each frames\n");
-  printf("   where: 'duration' is the duration in milliseconds,\n");
+  printf("   duration,frame      set duration of a particular frame\n");
-  printf("          'start' is the start frame index (optional)(default=1),\n");
+  printf("   duration,start,end  set duration of frames in the\n");
-  printf("          'end' is the inclusive end frame index (optional).\n");
+  printf("                        interval [start,end])\n");
-  printf("           The special value '0' means: last frame (default=0).\n");
+  printf("   where: 'duration' is the duration in milliseconds\n");
+  printf("          'start' is the start frame index\n");
+  printf("          'end' is the inclusive end frame index\n");
+  printf("           The special 'end' value '0' means: last frame.\n");
 
   printf("\n");
   printf("STRIP_OPTIONS:\n");
@@ -1053,12 +1056,19 @@ static int Process(const WebPMuxConfig* config) {
             ERROR_GOTO1("ERROR: duration must be strictly positive.\n", Err3);
           }
 
-          start = (nb_args >= 2) ? args[1] : 1;
+          if (nb_args == 1) {   // only duration is present -> use full interval
-          if (start <= 0) start = 1;
+            start = 1;
-
+            end = num_frames;
-          end = (nb_args >= 3) ? args[2] : num_frames;
+          } else {
-          if (end == 0) end = num_frames;
+            start = args[1];
-          if (end > num_frames) end = num_frames;
+            if (start <= 0) {
+              start = 1;
+            } else if (start > num_frames) {
+              start = num_frames;
+            }
+            end = (nb_args >= 3) ? args[2] : start;
+            if (end == 0 || end > num_frames) end = num_frames;
+          }
 
           for (k = start; k <= end; ++k) {
             assert(k >= 1 && k <= num_frames);
@@ -1085,7 +1095,7 @@ static int Process(const WebPMuxConfig* config) {
         mux = new_mux;  // transfer for the WebPMuxDelete() call
         new_mux = NULL;
 
-  Err3:
+ Err3:
         free(durations);
         WebPMuxDelete(new_mux);
         if (!ok) goto Err2;

man/webpmux.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH WEBPMUX 1 "November 8, 2016"
+.TH WEBPMUX 1 "November 10, 2016"
 .SH NAME
 webpmux \- create animated WebP files from non\-animated WebP images, extract
 frames from animated WebP images, and manage XMP/EXIF metadata and ICC profile.
@@ -99,17 +99,39 @@ Strip EXIF metadata.
 Strip XMP metadata.
 
 .SS DURATION_OPTIONS (\-duration)
-Amend the duration of a specific interval of frames.
+Amend the duration of a specific interval of frames. This option is only
+effective on animated WebP and has no effect on a single-frame file.
 .TP
 .I duration[,start[,end]]
 Where:
- 'duration' is the duration for the interval (mandatory). Must be non-negative.
+.br
- 'start' is the starting frame index of the interval (optional). If 'start'
+.B duration
-is less or equal to '1', its value will be set to '1'.
+is the duration for the interval in milliseconds (mandatory).
- 'end' is the ending frame index (inclusive) of the interval (optional). The
+Must be non-negative.
-value '0' has the special meaning 'last frame of the animation'.
+.br
+.B start
+is the starting frame index of the interval (optional).
+.br
+.B end
+is the ending frame index (inclusive) of the interval (optional).
+.TP
+The three typical usages of this option are:
+.br
+.B -duration d
+     set the duration to 'd' for the whole animation.
+.br
+.B -duration d,f
+     set the duration of frame 'f' to 'd'.
+.br
+.B -duration d,start,end
+     set the duration to 'd' for the whole [start,end] interval.
+.TP
+.P
 Note that the frames outside of the [start, end] interval will remain untouched.
-.I Reminder: frame indexing starts at '1'.
+The 'end' value '0' has the special meaning 'last frame of the animation'.
+.TP
+.I Reminder:
+frame indexing starts at '1'.
 .br
 
 .SS FRAME_OPTIONS (\-frame)