avcodec/libzvbi-teletextdec: allow -1 subtitle duration and make it the default

Most decoders (pgssubdec, ccaption_dec) are using -1 or UINT32_MAX for a
subtitle event which should be cleared at the next event.
Signed-off-by: Marton Balint <cus@passwd.hu>

doc/decoders.texi

@@ -272,7 +272,8 @@ present between the subtitle lines because of double-sized teletext characters.
 Default value is 1.
 @item txt_duration
 Sets the display duration of the decoded teletext pages or subtitles in
-milliseconds. Default value is 30000 which is 30 seconds.
+milliseconds. Default value is -1 which means infinity or until the next
+subtitle event comes.
 @item txt_transparent
 Force transparent background of the generated teletext bitmaps. Default value
 is 0 which means an opaque background.

libavcodec/libzvbi-teletextdec.c

@@ -548,7 +548,7 @@ static const AVOption options[] = {
     {"txt_left",        "x offset of generated bitmaps",                     OFFSET(x_offset),       AV_OPT_TYPE_INT,    {.i64 = 0},        0, 65535,    SD},
     {"txt_top",         "y offset of generated bitmaps",                     OFFSET(y_offset),       AV_OPT_TYPE_INT,    {.i64 = 0},        0, 65535,    SD},
     {"txt_chop_spaces", "chops leading and trailing spaces from text",       OFFSET(chop_spaces),    AV_OPT_TYPE_INT,    {.i64 = 1},        0, 1,        SD},
-    {"txt_duration",    "display duration of teletext pages in msecs",       OFFSET(sub_duration),   AV_OPT_TYPE_INT,    {.i64 = 30000},    0, 86400000, SD},
+    {"txt_duration",    "display duration of teletext pages in msecs",       OFFSET(sub_duration),   AV_OPT_TYPE_INT,    {.i64 = -1},      -1, 86400000, SD},
     {"txt_transparent", "force transparent background of the teletext",      OFFSET(transparent_bg), AV_OPT_TYPE_INT,    {.i64 = 0},        0, 1,        SD},
     {"txt_opacity",     "set opacity of the transparent background",         OFFSET(opacity),        AV_OPT_TYPE_INT,    {.i64 = -1},      -1, 255,      SD},
     { NULL },

libavcodec/version.h

@@ -29,7 +29,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR  58
 #define LIBAVCODEC_VERSION_MINOR  19
-#define LIBAVCODEC_VERSION_MICRO 100
+#define LIBAVCODEC_VERSION_MICRO 101
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \