lavfi/testsrc: make use of AV_OPT_TYPE_DURATION

Simplify.

libavfilter/vsrc_testsrc.c

@@ -53,7 +53,6 @@ typedef struct {
     unsigned int nb_frame;
     AVRational time_base, frame_rate;
     int64_t pts;
-    char *duration_str;         ///< total duration of the generated video
     int64_t duration;           ///< duration expressed in microseconds
     AVRational sar;             ///< sample aspect ratio
     int nb_decimals;
@@ -80,8 +79,8 @@ typedef struct {
     { "s",        "set video size",     OFFSET(w),        AV_OPT_TYPE_IMAGE_SIZE, {.str = "320x240"}, 0, 0, FLAGS },\
     { "rate",     "set video rate",     OFFSET(frame_rate), AV_OPT_TYPE_VIDEO_RATE, {.str = "25"}, 0, 0, FLAGS },\
     { "r",        "set video rate",     OFFSET(frame_rate), AV_OPT_TYPE_VIDEO_RATE, {.str = "25"}, 0, 0, FLAGS },\
-    { "duration", "set video duration", OFFSET(duration_str), AV_OPT_TYPE_STRING, {.str = NULL},   0, 0, FLAGS },\
-    { "d",        "set video duration", OFFSET(duration_str), AV_OPT_TYPE_STRING, {.str = NULL},   0, 0, FLAGS },\
+    { "duration", "set video duration", OFFSET(duration), AV_OPT_TYPE_DURATION, {.i64 = -1}, -1, INT64_MAX, FLAGS },\
+    { "d",        "set video duration", OFFSET(duration), AV_OPT_TYPE_DURATION, {.i64 = -1}, -1, INT64_MAX, FLAGS },\
     { "sar",      "set video sample aspect ratio", OFFSET(sar), AV_OPT_TYPE_RATIONAL, {.dbl= 1},  0, INT_MAX, FLAGS },
 
 
@@ -108,13 +107,6 @@ static av_cold int init(AVFilterContext *ctx)
     TestSourceContext *test = ctx->priv;
     int ret = 0;
 
-    test->duration = -1;
-    if (test->duration_str &&
-        (ret = av_parse_time(&test->duration, test->duration_str, 1)) < 0) {
-        av_log(ctx, AV_LOG_ERROR, "Invalid duration: '%s'\n", test->duration_str);
-        return ret;
-    }
-
     if (test->nb_decimals && strcmp(ctx->filter->name, "testsrc")) {
         av_log(ctx, AV_LOG_WARNING,
                "Option 'decimals' is ignored with source '%s'\n",