Support comments in preset files.

Originally committed as revision 15366 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -3718,7 +3718,7 @@ static int opt_bsf(const char *opt, const char *arg)
 static int opt_preset(const char *opt, const char *arg)
 {
     FILE *f=NULL;
-    char tmp[1000], tmp2[1000];
+    char tmp[1000], tmp2[1000], line[1000];
     int i;
     const char *base[3]= { getenv("HOME"),
                            "/usr/local/share",
@@ -3743,8 +3743,11 @@ static int opt_preset(const char *opt, const char *arg)
     }
 
     while(!feof(f)){
-        int e= fscanf(f, "%999[^=]=%999[^\n]\n", tmp, tmp2);
-        if(e!=2){
+        int e= fscanf(f, "%999[^\n]\n", line) - 1;
+        if(line[0] == '#' && !e)
+            continue;
+        e|= sscanf(line, "%999[^=]=%999[^\n]\n", tmp, tmp2) - 2;
+        if(e){
             fprintf(stderr, "Preset file invalid\n");
             av_exit(1);
         }