avconv: print an error on applying options of the wrong type.

I.e. input options to output files or vice versa.

cmdutils.c

@@ -351,6 +351,16 @@ int parse_optgroup(void *optctx, OptionGroup *g)
     for (i = 0; i < g->nb_opts; i++) {
         Option *o = &g->opts[i];
 
+        if (g->group_def->flags &&
+            !(g->group_def->flags & o->opt->flags)) {
+            av_log(NULL, AV_LOG_ERROR, "Option %s (%s) cannot be applied to "
+                   "%s %s -- you are trying to apply an input option to an "
+                   "output file or vice versa. Move this option before the "
+                   "file it belongs to.\n", o->key, o->opt->help,
+                   g->group_def->name, g->arg);
+            return AVERROR(EINVAL);
+        }
+
         av_log(NULL, AV_LOG_DEBUG, "Applying option %s (%s) with argument %s.\n",
                o->key, o->opt->help, o->val);
 

cmdutils.h

@@ -144,6 +144,8 @@ typedef struct OptionDef {
                                    an int containing element count in the array. */
 #define OPT_TIME  0x10000
 #define OPT_DOUBLE 0x20000
+#define OPT_INPUT  0x40000
+#define OPT_OUTPUT 0x80000
      union {
         void *dst_ptr;
         int (*func_arg)(void *, const char *, const char *);
@@ -224,6 +226,11 @@ typedef struct OptionGroupDef {
      * are terminated by a non-option argument (e.g. avconv output files)
      */
     const char *sep;
+    /**
+     * Option flags that must be set on each option that is
+     * applied to this group
+     */
+    int flags;
 } OptionGroupDef;
 
 typedef struct OptionGroup {